L‐ and T‐ Type Calcium Channels in Cerebral Arteries

Abstract

This study examined the expression, localization, and functional properties of voltage gated Ca2+channels in cerebral arterial smooth muscle cells. An initial PCR and western blot analysis, performed on whole arteries and isolated smooth muscle cells, revealed that the α1 subunits of L‐type (Cav1.2) and T‐type (Cav3.1 and Cav3.2) Ca2+ channels were present in these tissues. Immunohistochemistry confirmed the presence of all 3 Ca2+ channel subunits in specified cellular regions. Cav1.2 labeling was ribbon‐like along the length of the smooth muscle cell whereas T‐type labeling was punctate and localized to periodically spaced regions. Whole cell patch clamp electrophysiology confirmed the presence of a Ca2+current that was only partly blocked by nifedipine, an L‐type Ca2+ channel inhibitor. Characteristic of T‐type Ca2+ channels, the nifedipine‐insensitive component displayed fast inactivation kinetics and was abolished by mibefradil, efondipine and kurtoxin. Pressure myography experiments subsequently revealed that arterial tone was differential affected by L‐ and T‐type Ca2+ channel blockade depending on whether the vessel was pressurized to 20 or 80 mmHg. This differential effect was consistent with the voltage‐dependent properties of the two channel subtypes. In closing, this study found that L‐ and T‐type Ca2+ channels are expressed in cerebral arterial smooth muscle and that both contribute to tone development in accordance within their defined electrophysiological properties. Supported by CIHR.