Voltage-sensitive calcium channels (VSCC) mediate the entry of calcium ions into excitable cells and are also involved in a variety of calcium-dependent processes, including muscle contraction, hormone or neurotransmitter release, gene expression, cell motility, cell division and cell death. The isoform alpha-1C gives rise to L-type calcium currents. Long-lasting (L-type) calcium channels belong to the 'high-voltage activated' (HVA) group. They are blocked by dihydropyridines (DHP), phenylalkylamines, benzothiazepines, and by omega-agatoxin-IIIA (omega-Aga-IIIA). They are however insensitive to omega-conotoxin-GVIA (omega-CTx-GVIA) and omega-agatoxin-IVA (omega-Aga-IVA). Calcium channels containing the alpha-1C subunit play an important role in excitation-contraction coupling in the heart. The various isoforms display marked differences in the sensitivity to DHP compounds. Binding of calmodulin or CABP1 at the same regulatory sites results in an opposit effects on the channel function.
Atherosclerosis is an inflammatory process characterized by proliferation and dedifferentiation of vascular smooth muscle cells (VSMC). Ca(v)1.2 calcium channels may have a role in atherosclerosis because they are essential for Ca(2+)-signal transduction in VSMC. The pore-forming Ca(v)1.2alpha1 subunit of the channel is subject to alternative splicing. Here, we investigated whether the Ca(v)1.2alpha1 splice variants are affected by atherosclerosis. VSMC were isolated by laser-capture microdissection from frozen sections of adjacent regions of arteries affected and not affected by atherosclerosis. In VSMC from nonatherosclerotic regions, RT-PCR analysis revealed an extended repertoire of Ca(v)1.2alpha1 transcripts characterized by the presence of exons 21 and 41A. In VSMC affected by atherosclerosis, expression of the Ca(v)1.2alpha1 transcript was reduced and the Ca(v)1.2alpha1 splice variants were replaced with the unique exon-22 isoform lacking exon 41A. Molecular remodeling of the Ca(v)1.2alpha1 subunits associated with atherosclerosis caused changes in electrophysiological properties of the channels, including the kinetics and voltage-dependence of inactivation, recovery from inactivation, and rundown of the Ca(2+) current. Consistent with the pathophysiological state of VSMC in atherosclerosis, cell culture data pointed to a potentially important association of the exon-22 isoform of Ca(v)1.2alpha1 with proliferation of VSMC. Our findings are consistent with a hypothesis that localized changes in cytokine expression generated by inflammation in atherosclerosis affect alternative splicing of the Ca(v)1.2alpha1 gene in the human artery that causes molecular and electrophysiological remodeling of Ca(v)1.2 calcium channels and possibly affects VSMC proliferation.
J. Biol. Chem. 272, 3560-3566 (1997)[PubMed:9013606]
The pore-forming alpha1C subunit is the principal component of the voltage-sensitive L-type Ca2+ channel. It has a long cytoplasmic carboxyl-terminal tail playing a critical role in channel gating. The expression of alpha1C subunits is characterized by alternative splicing, which generates its multiple isoforms. cDNA cloning points to a diversity of human hippocampus alpha1C transcripts in the region of exons 40-43 that encode a part of the 662-amino acid carboxyl terminus. We compared electrophysiological properties of the well defined 2138-amino acid alpha1C,77 channel isoform with two splice variants, alpha1C,72 and alpha1C,86. They contain alterations in the carboxyl terminus due to alternative splicing of exons 40-42. The 2157-amino acid alpha1C,72 isoform contains an insertion of 19 amino acids at position 1575. The 2139-amino acid alpha1C,86 has 80 amino acids replaced in positions 1572-1651 of alpha1C,77 by a non-identical sequence of 81 amino acids. When expressed in Xenopus oocytes, all three splice variants retained high sensitivity toward dihydropyridine blockers but showed large differences in gating properties. Unlike alpha1C,77 and alpha1C,72, Ba2+ currents (IBa) through alpha1C,86 inactivated 8-10 times faster at +20 mV, and its inactivation rate was strongly voltage-dependent. Compared to alpha1C,77, the inactivation curves of IBa through alpha1C,86 and alpha1C,72 channels were shifted toward more negative voltages by 11 and 6 mV, respectively. Unlike alpha1C,77 and alpha1C,72, the alpha1C,86 channel lacks a Ca2+-dependent component of inactivation. Thus the segment 1572-1651 of the cytoplasmic tail of alpha1C is critical for the kinetics as well as for the Ca2+ and voltage dependence of L-type Ca2+ channel gating.
Smooth muscle exhibits mechanosensitivity independent of neural input, suggesting that mechanosensitive pathways reside within smooth muscle cells. The native L-type calcium current recorded from human intestinal smooth muscle is modulated by stretch. To define mechanosensitive mechanisms involved in the regulation of smooth muscle calcium entry, we cloned the alpha(1C) L-type calcium channel subunit (Ca(V)1.2) from human intestinal smooth muscle and expressed the channel in a heterologous system. This channel subunit retained mechanosensitivity when expressed alone or coexpressed with a beta(2) calcium channel subunit in HEK-293 or Chinese hamster ovary cells. The heterologously expressed human cardiac alpha(1C) splice form also demonstrated mechanosensitivity. Inhibition of kinase signaling did not affect mechanosensitivity of the native channel. Truncation of the alpha(1C) COOH terminus, which contains an inhibitory domain and a proline-rich domain thought to mediate mechanosensitive signaling from integrins, did not disrupt mechanosensitivity of the expressed channel. These data demonstrate mechanical regulation of calcium entry through molecularly identified L-type calcium channels in mammalian cells and suggest that the mechanosensitivity resides within the pore forming alpha(1C)-subunit.
Proc. Natl. Acad. Sci. U.S.A. 90, 6228-6232 (1993)[PubMed:8392192]
A unique structural variant of the cardiac L-type voltage-dependent calcium channel alpha 1 subunit cDNA was isolated from libraries derived from normal human heart mRNA. The deduced amino acid sequence shows significant homology to other calcium channel alpha 1 subunits. However, differences from the rabbit heart alpha 1 include a shortened N-terminus, a unique C-terminal insertion, and both forms of an alternatively spliced motif IV S3 region. The shortened N-terminus provides optimal access to consensus sequences thought to facilitate translation. Northern blot analysis revealed a single hybridizing mRNA species of 9.4 kb. The gene for the human heart alpha 1 subunit was localized specifically to the distal region of chromosome 12p13. The cloned alpha 1 subunit was expressed in Xenopus oocytes and single-channel analyses revealed native-like pharmacology and channel properties.
J. Biol. Chem. 270, 10540-10543 (1995)[PubMed:7737988]
Voltage-dependent inhibition by 1,4-dihydropyridines is a characteristic property of L-type Ca2+ channels. Six out of 50 exons of the channel alpha 1C subunit gene are subjected to alternative splicing, thus generating channel isoform diversity. Using Xenopus oocytes as an expression system, we have found that transmembrane segment IIIS2 of human alpha 1C subunit is involved in the control of voltage dependence of dihydropyridine action. This segment is genetically regulated through alternative splicing of exons 21/22. Site-directed mutagenesis points to two amino acids in IIIS2, which determine the difference of the splice variants in their sensitivities to dihydropyridines. This finding provides new insight into molecular mechanisms of Ca2+ channel inhibition by this important class of drugs.
L-type Ca2+ channels are important targets for drugs, such as dihydropyridines (DHPs), in the treatment of cardiovascular diseases. Channel expression is regulated by alternative splicing. It has been suggested that in the cardiovascular system tissue-specific expression of different L-type Ca2+ channel splice variants may underlie the observed differences in sensitivities to channel block by DHPs. We investigated the sensitivity of Ca2+ channel splice variants derived from the human alpha1C gene to the DHP isradipine. Among seven alpha1C channels we observed up to 10-fold differences in IC50 values for isradipine, as well as changes in the voltage dependence of DHP action.
Interacting selectively and non-covalently with alpha-actinin, one of a family of proteins that cross-link F-actin as antiparallel homodimers. Alpha-actinin has a molecular mass of 93-103 KDa; at the N-terminus there are two calponin homology domains, at the C-terminus there are two EF-hands. These two domains are connected by the rod domain. This domain is formed by triple-helical spectrin repeats.
Evidence
1:
Inferred from Physical InteractionBHF-UCL
Cytoskeletal proteins are known to sculpt the structural architecture of cells. However, their role as bridges linking the functional crosstalk of different ion channels is unknown. Here, we demonstrate that a small conductance Ca(2+)-activated K(+) channels (SK2 channel), present in a variety of cells, where they integrate changes in intracellular Ca(2+) concentration [Ca(2+)(i)] with changes in K(+) conductance and membrane potential, associate with L-type Ca(2+) channels; Ca(v)1.3 and Ca(v)1.2 through a physical bridge, alpha-actinin2 in cardiac myocytes. SK2 channels do not physically interact with L-type Ca(2+) channels, instead, the 2 channels colocalize via their interaction with alpha-actinin2 cytoskeletal protein. The association of SK2 channel with alpha-actinin2 localizes the channel to the entry of external Ca(2+) source, which regulate the channel function. Furthermore, we demonstrated that the functions of SK2 channels in atrial myocytes are critically dependent on the normal expression of Ca(v)1.3 Ca(2+) channels. Null deletion of Ca(v)1.3 channel results in abnormal function of SK2 channel and prolongation of repolarization and atrial arrhythmias. Our study provides insight into the molecular mechanisms of the coupling of SK2 channel with voltage-gated Ca(2+) channel, and represents the first report linking the coupling of 2 different types of ion channels via cytoskeletal proteins.
Interacting selectively and non-covalently with calmodulin, a calcium-binding protein with many roles, both in the calcium-bound and calcium-free states.
Evidence
1:
Inferred from Physical InteractionUniProtKB
Ca2+-binding protein-1 (CaBP1) is a Ca2+-binding protein that is closely related to calmodulin (CaM) and localized in somatodendritic regions of principal neurons throughout the brain, but how CaBP1 participates in postsynaptic Ca2+ signaling is not known. Here, we describe a novel role for CaBP1 in the regulation of Ca2+ influx through Ca(v)1.2 (L-type) Ca2+ channels. CaBP1 interacts directly with the alpha1 subunit of Ca(v)1.2 at sites that also bind CaM. CaBP1 binding to one of these sites, the IQ domain, is Ca2+ dependent and competitive with CaM binding. The physiological significance of this interaction is supported by the association of Ca(v)1.2 and CaBP1 in postsynaptic density fractions purified from rat brain. Moreover, in double-label immunofluorescence experiments, CaBP1 and Ca(v)1.2 colocalize in numerous cell bodies and dendrites of neurons, particularly in pyramidal cells in the CA3 region of the hippocampus and in the dorsal cortex. In electrophysiological recordings of cells transfected with Ca(v)1.2, CaBP1 greatly prolonged Ca2+ currents, prevented Ca2+-dependent inactivation, and caused Ca2+-dependent facilitation of currents evoked by step depolarizations and repetitive stimuli. These effects contrast with those of CaM, which promoted strong Ca2+-dependent inactivation of Ca(v)1.2 with these same voltage protocols. Our findings reveal how Ca2+-binding proteins, such as CaM and CaBP1, differentially adjust Ca2+ influx through Ca(v)1.2 channels, which may specify diverse modes of Ca2+ signaling in neurons.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionUniProtKB
To define the role of the Rab3-interacting molecule RIM in exocytosis we searched for additional binding partners of the protein. We found that the two C(2) domains of RIM display properties analogous to those of the C(2)B domain of synaptotagmin-I. Thus, RIM-C(2)A and RIM-C(2)B bind in a Ca(2+)-independent manner to alpha1B, the pore-forming subunit of N-type Ca(2+) channels (EC(50) = approximately 20 nm). They also weakly interact with the alpha1C but not the alpha1D subunit of L-type Ca(2+) channels. In addition, the C(2) domains of RIM associate with SNAP-25 and synaptotagmin-I. The binding affinities for these two proteins are 203 and 24 nm, respectively, for RIM-C(2)A and 224 and 16 nm for RIM-C(2)B. The interactions of the C(2) domains of RIM with SNAP-25 and synaptotagmin-I are modulated by Ca(2+). Thus, in the presence of Ca(2+) (EC(50) = approximately 75 microm) the interaction with synaptotagmin-I is increased, whereas SNAP-25 binding is reduced. Synaptotagmin-I binding is abolished by mutations in two positively charged amino acids in the C(2) domains of RIM and by the addition of inositol polyphosphates. We propose that the Rab3 effector RIM is a scaffold protein that participates through its multiple binding partners in the docking and fusion of secretory vesicles at the release sites.
Evidence
2:
Inferred from Physical InteractionUniProtKB
Ca2+-binding protein-1 (CaBP1) is a Ca2+-binding protein that is closely related to calmodulin (CaM) and localized in somatodendritic regions of principal neurons throughout the brain, but how CaBP1 participates in postsynaptic Ca2+ signaling is not known. Here, we describe a novel role for CaBP1 in the regulation of Ca2+ influx through Ca(v)1.2 (L-type) Ca2+ channels. CaBP1 interacts directly with the alpha1 subunit of Ca(v)1.2 at sites that also bind CaM. CaBP1 binding to one of these sites, the IQ domain, is Ca2+ dependent and competitive with CaM binding. The physiological significance of this interaction is supported by the association of Ca(v)1.2 and CaBP1 in postsynaptic density fractions purified from rat brain. Moreover, in double-label immunofluorescence experiments, CaBP1 and Ca(v)1.2 colocalize in numerous cell bodies and dendrites of neurons, particularly in pyramidal cells in the CA3 region of the hippocampus and in the dorsal cortex. In electrophysiological recordings of cells transfected with Ca(v)1.2, CaBP1 greatly prolonged Ca2+ currents, prevented Ca2+-dependent inactivation, and caused Ca2+-dependent facilitation of currents evoked by step depolarizations and repetitive stimuli. These effects contrast with those of CaM, which promoted strong Ca2+-dependent inactivation of Ca(v)1.2 with these same voltage protocols. Our findings reveal how Ca2+-binding proteins, such as CaM and CaBP1, differentially adjust Ca2+ influx through Ca(v)1.2 channels, which may specify diverse modes of Ca2+ signaling in neurons.
Catalysis of the transmembrane transfer of a calcium ion by a voltage-gated channel. A voltage-gated channel is a channel whose open state is dependent on the voltage across the membrane in which it is embedded.
Proc. Natl. Acad. Sci. U.S.A. 90, 6228-6232 (1993)[PubMed:8392192]
A unique structural variant of the cardiac L-type voltage-dependent calcium channel alpha 1 subunit cDNA was isolated from libraries derived from normal human heart mRNA. The deduced amino acid sequence shows significant homology to other calcium channel alpha 1 subunits. However, differences from the rabbit heart alpha 1 include a shortened N-terminus, a unique C-terminal insertion, and both forms of an alternatively spliced motif IV S3 region. The shortened N-terminus provides optimal access to consensus sequences thought to facilitate translation. Northern blot analysis revealed a single hybridizing mRNA species of 9.4 kb. The gene for the human heart alpha 1 subunit was localized specifically to the distal region of chromosome 12p13. The cloned alpha 1 subunit was expressed in Xenopus oocytes and single-channel analyses revealed native-like pharmacology and channel properties.
Methylmercury (MeHg) disrupts the function of native, high voltage-activated neuronal Ca(2+) channels in several types of cells. However, the effects of MeHg on isolated Ca(2+) channel phenotypes have not been examined. The aim of the present study was to examine the action of MeHg on recombinant, neuronal L-type voltage-sensitive Ca(2+) channels. Human embryonic kidney cells (HEK-293) were transfected with human neuronal cDNA clones of the alpha(1C-1) subunit in combination with alpha(2b) and beta(3a) Ca(2+) channel subunits and the reporter jellyfish green fluorescent protein for transient expression. Current from expressed channels (I(Ba)) and their response to MeHg applied acutely were measured using whole-cell voltage-clamp recording techniques and Ba(2+) (5 mM) as charge carrier. Amplitude of I(Ba) in these cells was reduced by the dihydropyridine (DHP), nimodipine, and enhanced by Bay K8644 [S-(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-[trifluoromethyl]phenyl)-3 pyridine carboxylic acid methyl ester]. MeHg (0.125-5.0 microM) caused a time- and concentration-dependent reduction in amplitude of the peak and sustained current through these channels. However, even at the highest concentration of MeHg tested, reduction of current amplitude by MeHg was incomplete. Washing with MeHg-free solution could not reverse its effects. The steady-state inactivation curve was unaltered by MeHg. Increasing the stimulation frequency or the extracellular Ba(2+) concentration each attenuated slightly the reduction in amplitude of I(Ba) by MeHg. In the presence of MeHg (5.0 microM), Bay K8644 still increased the remaining current, and nimodipine (10 microM) reduced residual current that was resistant to MeHg. Thus, although MeHg reduces the amplitude of recombinant, heterologously expressed L-type channel current, a portion of current is resistant to reduction by MeHg. Furthermore, DHP agonists and antagonists retain their ability to affect L-type Ca(2+) channel current even in the presence of MeHg.
The actions or reactions of an adult relating to the progression of that organism along the ground by the process of lifting and setting down each leg.
Ca(2+) mobilization from intracellular stores is mediated by Ca(2+) release channels, designated ryanodine and IP(3) receptors, and directly regulates important cellular reactions including muscle contraction, endo/exocrine secretion, and neural excitability. In order to function as an intracellular store, the endo/sarcoplasmic reticulum is equipped with cooperative Ca(2+) uptake, storage and release machineries, comprising synergic collaborations among integral-membrane, cytoplasmic and luminal proteins. Our recent studies have demonstrated that junctophilins form junctional membrane complexes between the plasma membrane and the endo/sarcoplasmic reticulum in excitable cells, and that TRIC (trimeric intracellular cation) channels act as novel monovalent cation-specific channels on intracellular membrane systems. Knockout mice have provided evidence that both junctophilins and TRIC channels support efficient ryanodine receptor-mediated Ca(2+) release in muscle cells. This review focuses on cardiac Ca(2+) release by discussing pathological defects of mutant cardiomyocytes lacking ryanodine receptors, junctophilins, or TRIC channels.
The release of intracellular molecules (e.g. hormones, matrix proteins) contained within a membrane-bounded vesicle by fusion of the vesicle with the plasma membrane of a cell, requiring the presence of calcium ions.
Methylmercury (MeHg) disrupts the function of native, high voltage-activated neuronal Ca(2+) channels in several types of cells. However, the effects of MeHg on isolated Ca(2+) channel phenotypes have not been examined. The aim of the present study was to examine the action of MeHg on recombinant, neuronal L-type voltage-sensitive Ca(2+) channels. Human embryonic kidney cells (HEK-293) were transfected with human neuronal cDNA clones of the alpha(1C-1) subunit in combination with alpha(2b) and beta(3a) Ca(2+) channel subunits and the reporter jellyfish green fluorescent protein for transient expression. Current from expressed channels (I(Ba)) and their response to MeHg applied acutely were measured using whole-cell voltage-clamp recording techniques and Ba(2+) (5 mM) as charge carrier. Amplitude of I(Ba) in these cells was reduced by the dihydropyridine (DHP), nimodipine, and enhanced by Bay K8644 [S-(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-[trifluoromethyl]phenyl)-3 pyridine carboxylic acid methyl ester]. MeHg (0.125-5.0 microM) caused a time- and concentration-dependent reduction in amplitude of the peak and sustained current through these channels. However, even at the highest concentration of MeHg tested, reduction of current amplitude by MeHg was incomplete. Washing with MeHg-free solution could not reverse its effects. The steady-state inactivation curve was unaltered by MeHg. Increasing the stimulation frequency or the extracellular Ba(2+) concentration each attenuated slightly the reduction in amplitude of I(Ba) by MeHg. In the presence of MeHg (5.0 microM), Bay K8644 still increased the remaining current, and nimodipine (10 microM) reduced residual current that was resistant to MeHg. Thus, although MeHg reduces the amplitude of recombinant, heterologously expressed L-type channel current, a portion of current is resistant to reduction by MeHg. Furthermore, DHP agonists and antagonists retain their ability to affect L-type Ca(2+) channel current even in the presence of MeHg.
The regulated release of proinsulin from secretory granules (B granules) in the B cells of the pancreas; accompanied by cleavage of proinsulin to form mature insulin.
Any process that modulates the force with which blood travels through the circulatory system. The process is controlled by a balance of processes that increase pressure and decrease pressure.
The process leading to shortening and/or development of tension in the urinary bladder smooth muscle tissue involved in the expulsion urine from the body.
Protein involved in the transport of calcium ions. Calcium is essential for a variety of bodily functions, such as neurotransmission, muscle contraction and proper heart function.
Protein involved in the transport of ions. Such proteins are usually transmembrane and mediate a movement of ions across cell membranes. Transport may be passive (facilitated diffusion; down the electrochemical gradient), or active (against the electrochemical gradient). Active transport requires energy which may come from light, oxidation reactions, ATP hydrolysis, or cotransport of other ions or molecules.
Protein involved in the transport of a molecule (metabolite, protein, etc), a ion or an electron across cell membranes, inside the cell or in a tissue fluid.
Cell membrane glycoprotein forming a channel in a biological membrane selectively permeable to calcium ions. Calcium is essential for a variety of bodily functions, such as neurotransmission, muscle contraction and proper heart function.
Protein which is part of a transmembrane protein complex that forms a hydrophilic channel across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients. The channels are usually gated and only open in response to a specific stimulus, such as a change in membrane potential (voltage-gated) or the binding of a ligand (ligand-gated channel).
Protein which is a component of a voltage-gated channel. Voltage-gated ion channels are responsible for the electrical activity in a variety of cell types. They probably exist in all life forms.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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