Indirect coupling between Cav1.2 channels and ryanodine receptors to generate Ca2+ sparks in murine arterial smooth muscle cells

In arterial vascular smooth muscle cells (VSMCs), Ca2+ sparks stimulate nearby Ca2+-activated K+ (BK) channels that hyperpolarize the membrane and close L-type Ca2+ channels. We tested the contribution of L-type Ca(v)1.2 channels to Ca2+ spark regulation in tibial and cerebral artery VSMCs using VSMC-specific Ca(v)1.2 channel gene disruption in (SMAKO) mice and an approach based on Poisson statistical analysis of activation frequency and first latency of elementary events. Ca(v)1.2 channel gene inactivation reduced Ca2+ spark frequency and amplitude by similar to 50% and similar to 80%, respectively. These effects were associated with lower global cytosolic Ca2+ levels and reduced sarcoplasmic reticulum (SR) Ca2+ load. Elevating cytosolic Ca2+ levels reversed the effects completely. The activation frequency and first latency of elementary events in both wild-type and SMAKO VSMCs weakly reflected the voltage dependency of L-type channels. This study provides evidence that local and tight coupling between the Ca(v)1.2 channels and ryanodine receptors (RyRs) is not required to initiate Ca2+ sparks. Instead, Ca(v)1.2 channels contribute to global cytosolic [Ca2+], which in turn influences luminal SR calcium and thus Ca2+ sparks.