Figure 4.

Calcium signaling in feed arteries versus downstream arterioles. Feed arteries display both Ca²⁺ sparks and Ca²⁺ waves, as shown. Ca²⁺ sparks in feed arteries arise from RyRs that may be activated by Ca²⁺ influx through Ca_V 3.2 channels via Ca²⁺-induced Ca²⁺ release. In feed arteries, Ca²⁺ sparks activate BK_Ca channels, hyperpolarizing the membrane and deactivating Ca_V 1.2 channels, which contributes to the negative feedback regulation of myogenic tone. Ca²⁺ waves in feed arteries depend on the activity of both RyRs and IP₃Rs. In arterioles, Ca²⁺ influx through Ca_V 1.2 and other VGCCs provides the Ca²⁺ signal for activation of BK_Ca channels and the negative feedback regulation of membrane potential and VGCC activity. Ca²⁺ waves in arterioles depend solely on the activity of IP₃R. RyRs are expressed in arteriolar SMCs but are silent under resting conditions. See text for details.