Figure 7. Vascular smooth muscle L-type calcium channel calcium sparklets.

Cav1.2 L-type Ca²⁺ channels (L) in the vascular smooth muscle cell plasma membrane (VSMC PM) produce highly localized Ca²⁺ influx events (i.e., Ca²⁺ sparklets). Brief stochastic opening of single L-type Ca²⁺ channels produce low activity Ca²⁺ sparklet sites while prolonged opening of one or more clustered L-type Ca²⁺ channels produce high activity Ca²⁺ sparklet sites. Ca²⁺ influx from low and high activity Ca²⁺ sparklet sites contribute to global intracellular Ca²⁺ ([Ca²⁺]_i) resulting in contraction. Elevated Ca²⁺ concentrations at high activity Ca²⁺ sparklet sites (and perhaps global intracellular Ca²⁺ as well) contribute to changes in gene expression associated with increased contraction.