The smooth muscle cells of resistance arteries depolarize and contract when intravascular pressure is elevated. This is a central characteristic of myogenic tone, which plays an important role in regulation of blood flow in many vascular beds. Pressure-induced vascular smooth muscle depolarization depends in part on the activation of cation channels. Here, we show that activation of these smooth muscle cation channels and pressure-induced depolarization are mediated by protein kinase C in cerebral resistance arteries. Diacylglycerol, phorbol myristate acetate, and cell swelling activate a cation current that we have previously shown is mediated by transient receptor potential channels. These currents, as well as the smooth muscle cell depolarizations of intact arteries induced by diacylglycerol, phorbol ester, and elevation of intravascular pressure, are nearly eliminated by protein kinase C inhibitors. These results suggest a major mechanism of myogenic tone involves mechanotransduction through phospholipase C, diacylglycerol production, and protein kinase C activation, which increase cation channel activity. The associated depolarization activates L-type calcium channels, leading to increased intracellular calcium and vasoconstriction.
Functional properties of a rabbit cardiac a, Cat* channel subunit (CARDa,) were investigated using the patch~lamp technique in mouse L cells, a recipient cell line which is devoid of any Ca*' channel subunits. Cell lines resulting from stable transfection of the CARDa, subunit as well as in coexpression with a B subunit (CARD@) derived from skeletal muscle (SKM were characterized. The results show that while the CARDa,-Ca2' channel activity is negligible, the Ba2' current density is dramati~lly increased in the presence of /3 subunit (-20-fold). CARD&,-and CARDa&Ba~' currents were both sensitive to the 1,4-dihydropyridine (DHP) agonist, Bay K 8644 (5-to S-fold increase). Activation kinetics of CARDa,-and CARD@-Ba2" currents were comparable. The inactivation time-course was faster (3-to 4-fold) for CARDa&Ba*+ currents. We conclude that the main role of the B subunit in heart is to modulate the L-type current density and present several lines of evidence that SKMa, and CARDa, are differentially regulated by the @ subunit.
Biochemical, pharmacological and electrophysiological evidence implies the existence of tissue specific isoforms of the L-type VDCC. The a, and a, subunits of the skeletal muscle calcium channel have been previously cloned and their ammo acid sequence deduced. Here we report the isolation and sequencing of a partial cDNA that encodes a heart specific isoform of the a, subunit. The amino acid sequence deduced from this part cDNA clone shows 64.7% similarity with the skeletal muscle ar subunit. Northern analysis reveals 2 hybridizing bands, 8.5 and 13 kb, in contrast to one 6.5 kb band in the skeletal muscle. Selective inhibition of mRNA expression in Xenopus oocytes by complementary oligodeoxynucleotides derived from the heart clone provides further evidence that the cDNA corresponds to an essential component of the VDCC. These data further support the existence of tissue-specific isoforrns of the L-type VDCC.
Native-type DHP-sensitive calcium channel currents are produced by cloned rat aortic smooth muscle and cardiac a, subunits expressed in Xempus laevis oocytes and are regulated by a2-and B-subunits
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.