Molecular Properties of Calcium Channels in Skeletal Muscle and Neurons (original) (raw)
Related papers
European Journal of Biochemistry, 1991
The cloning of the cDNA for the a1 subunit of L-type calcium channels revealed that at least two genes (CaChl and CaCh2) exist which give rise to several splice variants. The expression of mRNA for these a1 subunits and the skeletal muscle a2/6, p and y subunits was studied in rabbit tissues and BC3Hl cells. Nucleic-acidhybridization studies showed that the mRNA of all subunits are expressed in skeletal muscle, brain, heart and aorta. However, the al-, pand y-specific transcripts had different sizes in these tissues. Smooth muscle and heart contain different splice variants of the CaCh2 gene. The a l , /? and y mRNA are expressed together in differentiated but not in proliferating BC3H1 cells. A probe specific for the skeletal muscle a2/6 subunit did not hybridize to poly(A)-rich RNA from BC3Hl cells. These results suggest that different splice variants of the genes for the a l , jl and y subunits exist in tissues containing L-type calcium channels, and that their expression is regulated in a coordinate manner.
Molecular biology of calcium channels
Kidney International, 1995
The molecular biology of Ca2 channels has its origins in the biochemical characterization of the skeletal muscle dihydropyridine receptor. These studies established that the dihydropyridine receptor/channel complex was a multi-subunit complex composed of a1 (the ion-conducting subunit), and smaller accessory subunits (a2, /3, and y). These subunits were purified, sequenced, cloned, and expressed. Cloning of these cDNAs provided the probes to discover the molecular diversity of Ca2 channels. To date (April 1995), genes for six a1s, four /3s, one a2, and one y have been cloned. Preliminary classification schemes divided native calcium channels into low voltage-activated (T-type) and high voltageactivated types: L-type, dihydropyridine-sensitive; and N-type, w-conotoxin GVIA-sensitive. The development of new toxins has led to the further subclassification of high voltage-activated channels to: P-type, which is blocked by w-agatoxin-IVa from the funnel-web spider Agelenopsis aperta; Q-type, which is blocked by w-conotoxin-MVIIC from the marine snail Conus magus; and R-type, which is resistant to most toxins (DB Wheeler, A Randall, and RW Tsien, Science 264: 1994). Expression studies with cloned a1s have proven that this subunit determines the voltage and pharmacological sensitivity of the channel. This should allow us to classify the cloned a1s in terms of their type.
Calcium channels: Structure, function, and classification
Drug Development Research, 1994
Voltage-gated Ca2 ' channels have been exten5ively characterized in terms of their electrophysiological and pharmacological properties [McDonald et al. (1994). Physiol Rev 74. 365-507; Spedding and Paoletti (1992): Pharmacol Kev44:363-376; Tsien and Tsien (1990): Annu Rev Cell Biol 6:715-7601. These studies indicate that there are numerous types of Ca2+ channels, termed L, N, PIQ, R, and T [Zhang et al. (1993): Neuropharmacology 32:1075-10881. Biochemical and molecular biological studies have established that CaL+ channels are multi-subunit complexes composed of an ion-conducting subunit, al (see Fig. I ) , and smaller accessory subunits (a2, p, and sometimes y and a 95 kDa protein). To date (May, 19941, genes for six a , , four p, one u2, and one y have been cloned. Expression studies with cloned a1 have demonstrated that this whunit can determine the voltage and pharmacological sensitivity of the channel. This should allow us to classify the cloned a15 in terms of their type. Unfortunately life i s not that simple. We will review how the accessory subunits are capable of modifying the pharmacological and biophysical characteristics of the channel. Despite these complications, 5 of the 6 a , s can be clawfied as follows: (1) three (, and a q U ) belong to the L-type (dihydropyridine-sensitive), (2) ale is an N-type (w-conotoxin-GVIAsensitive), and (3) a,A is a P (w-aga-IVA-sensitive, also called Q [see : Neuropharmacology 32:1075-10881, herein referred to as PiQ). The sixth a,, aIE, does not display any distinctive pharmacology, thus it has been called an R-type (resistant) The molecular biology of Ca2+ channels has its origins in the biochemical characterization of the skeletal muscle dihydropyridine receptor. This receptorichannel complex was purified, sequenced, cloned, and expressed. Cloning of these cDNAs provided the probes to discover the molecular diversity of Ca2' channels. We will review the cloning, tissue distribution, and functional expression of a1 subunits following a historical path, then review the accessory subunits. o 19% Wdey LISS, Inc
Molecular Properties of Structure and Regulation of the Calcium Channela
Annals of the New York Academy of Sciences, 1988
Voltage-dependent calcium channels are known to play important roles in excitationcontraction coupling in cardiac and smooth muscles and also in a number of neurosecretory processes. They have recently become accessible to biochemical study as a result of the availability of a number of tritiated calcium channel inhibitors belonging to the dihydropyridine and the phenylalkylamine series.' Dihydropyridine derivatives such as nitrendipine and other calcium inhibitors such as verapamil, bepridil, and diltiazem are very important therapeutic agents in the treatment of cardiovascular disorders.' One of the difficulties associated with the biochemical characterization of macromolecules that confer electrical excitability to biological membranes, such as the voltage-sensitive calcium channel, is that they are almost always present in very low amounts in membranes. For most membrane preparations in which the voltagesensitive calcium channel has been characterized, the dihydropyridine receptor is only present at a density in the range of 0.1 to 1 pmol/mg protein.' Therefore, the transverse tubule (T-tubule) membrane preparation isolated from rabbit skeletal muscle appears to be exceptional in that it contains more than 50 pmol [3H]dihydropyridine-binding sites/mg p r~t e i n .~ Voltage-clamp analyses of skeletal muscle have shown that essentially all specific Ca'+ conductances are localized in the transverse tubular system and that the channel responsible for these conductances is inhibited by low concentrations 'This work was supported by the Association des Myopathes, the Centre National de la Recherche Scientifique, the Fondation sur les Maladies Vasculaires, the Fondation pour la Recherche Mkdicale, and the Ministere de I'Industrie et de la Recherche (grant no. 83.C.0696).
Molecular Properties of Structure and Regulation of the Calcium Channel
Annals of the New York Academy of Sciences, 1988
Voltage-dependent calcium channels are known to play important roles in excitationcontraction coupling in cardiac and smooth muscles and also in a number of neurosecretory processes. They have recently become accessible to biochemical study as a result of the availability of a number of tritiated calcium channel inhibitors belonging to the dihydropyridine and the phenylalkylamine series.' Dihydropyridine derivatives such as nitrendipine and other calcium inhibitors such as verapamil, bepridil, and diltiazem are very important therapeutic agents in the treatment of cardiovascular disorders.'
Different types of Ca2+ channels in mammalian skeletal muscle cells in culture
Proceedings of the National Academy of Sciences, 1986
This paper describes the existence of two pharmacologically distinct types of Ca2+ channels in rat skeletal muscle cells (myoballs) in culture. The first class of Ca2+ channels is insensitive to the dihydropyridine (DHP) (+)-PN 200-110; the second class of Ca2+ channels is blocked by low concentrations of (+)-PN 200-110. The two pharmacologically different Ca2+ channels are also different in their voltage and time dependence. The threshold for activation of the DHP-insensitive Ca2+ channel is near -65 mV, whereas the threshold for activation of the DHP-sensitive Ca2+ channel is near -30 mV. Current flowing through the DHP-insensitive Ca2+ channel is transient with relatively fast kinetics. Halfmaximal inactivation for the DHP-insensitive Ca2+ channel is observed at a holding potential Vho.5 = -78 mV and the channel is completely inactivated at -60 mV. Two different behaviors have been found for DHP-sensitive channels with two different kinetics of inactivation (one being about 16 times faster than the other at -2 mV) and two different voltage dependencies. These two different behaviors are often observed in the same myoball and may correspond to two different subtypes of DHP-sensitive Ca'+ channels or to two different modes of expression of one single Ca2+ channel protein.
FEBS Letters, 1993
Calcium channel blockers are drugs that bind to the a, subumt of L-type calcmm channels and selectively inhabit ion movements through these channels. Determinatton of the mechanism of channel blockade requires localizatton of drug-binding sues within the primary structure of the receptor. In thts study the 1,4-dihydropyridine-binding site of the membrane bound receptor has been identtfied. The covalently labeled receptor was purified and digested with trypsin. The labeled peptide fragments were immunoprecipitated with sequence-directed antibodies. The data indicate the existence of at least three distmct dihydropyridme-binding domains within the primary structure of the a, subunit.