Identification of L- and T-type Ca2+channels in rat cerebral arteries: role in myogenic tone development

Abstract

L-type Ca2+channels are broadly expressed in arterial smooth muscle cells, and their voltage-dependent properties are important in tone development. Recent studies have noted that these Ca2+channels are not singularly expressed in vascular tissue and that other subtypes are likely present. In this study, we ascertained which voltage-gated Ca2+channels are expressed in rat cerebral arterial smooth muscle and determined their contribution to the myogenic response. mRNA analysis revealed that the α1-subunit of L-type (Cav1.2) and T-type (Cav3.1 and Cav3.2) Ca2+channels are present in isolated smooth muscle cells. Western blot analysis subsequently confirmed protein expression in whole arteries. With the use of patch clamp electrophysiology, nifedipine-sensitive and -insensitive Ba2+currents were isolated and each were shown to retain electrical characteristics consistent with L- and T-type Ca2+channels. The nifedipine-insensitive Ba2+current was blocked by mibefradil, kurtoxin, and efonidpine, T-type Ca2+channel inhibitors. Pressure myography revealed that L-type Ca2+channel inhibition reduced tone at 20 and 80 mmHg, with the greatest effect at high pressure when the vessel is depolarized. In comparison, the effect of T-type Ca2+channel blockade on myogenic tone was more limited, with their greatest effect at low pressure where vessels are hyperpolarized. Blood flow modeling revealed that the vasomotor responses induced by T-type Ca2+blockade could alter arterial flow by ∼20–50%. Overall, our findings indicate that L- and T-type Ca2+channels are expressed in cerebral arterial smooth muscle and can be electrically isolated from one another. Both conductances contribute to myogenic tone, although their overall contribution is unequal.