Figure 3. Vascular smooth muscle calcium waves.

Norepinephrine (NE)-dependent stimulation of α₁ adrenergic receptors (α1R) on the vascular smooth muscle cell plasma membrane (VSMC PM) leads to activation of phospholipase C (PLC) and the production of inositol 1,4,5-trisphosphate (IP3). IP3 in turn promotes the opening of IP3 receptors (IP3R) on the sarcoplasmic reticulum (SR) resulting in a propagating series of Ca²⁺ release events (i.e., a Ca²⁺ wave). Ca²⁺ waves increase contraction directly by elevating global intracellular Ca²⁺ ([Ca²⁺]_i). Ca²⁺ waves also modulate contraction indirectly by altering plasma membrane potential (and thus voltage-dependent Ca²⁺ influx through Cav1.2 L-type Ca²⁺ channels) by stimulating plasmalemmal Ca²⁺-activated chloride channels.