Abnormal Coronary Function in Mice Deficient in α₁H T-type Ca2⁺ Channels

Calcium ion (Ca2+) influx through voltage-gated Ca2+channels is important for the regulation of vascular tone. Activation of L-type Ca2+channels initiates muscle contraction; however, the role of T-type Ca2+channels (T-channels) is not clear. We show that mice deficient in the$\alpha_{1H}$T-type Ca2+channel ($\alpha_13.2-null$) have constitutively constricted coronary arterioles and focal myocardial fibrosis. Coronary arteries isolated from$\alpha_13.2-null$arteries showed normal contractile responses, but reduced relaxation in response to acetylcholine and nitroprusside. Furthermore, acute blockade of T-channels with Ni2+prevented relaxation of wild-type coronary arteries. Thus, Ca2+influx through$\alpha_{1H}$T-type Ca2+channels is essential for normal relaxation of coronary arteries.