Opposing roles of smooth muscle BK channels and ryanodine receptors in the regulation of nerve-evoked constriction of mesenteric resistance arteries.

In depolarized smooth muscle cells of pressurized cerebral arteries, ryanodine receptors (RyRs) generate "Ca2+ sparks" that activate large-conductance, Ca2+ -, and voltage-sensitive potassium (BK) channels to oppose pressure-induced (myogenic) constriction. Here, we show that BK channels and RyRs have opposing roles in the regulation of arterial tone in response to sympathetic nerve activation by electrical field stimulation. Inhibition of BK channels with paxilline increased both myogenic and nerve-induced constrictions of pressurized, resistance-sized mesenteric arteries from mice. Inhibition of RyRs with ryanodine increased myogenic constriction, but it decreased nerve-evoked constriction along with a reduction in the amplitude of nerve-evoked increases in global intracellular Ca2+. In the presence of L-type voltage-dependent Ca2+ channel (VDCC) antagonists, nerve stimulation failed to evoke a change in arterial diameter, and BK channel and RyR inhibitors were without effect, suggesting that nerve- induced constriction is dependent on activation of VDCCs. Collectively, these results indicate that BK channels and RyRs have different roles in the regulation of myogenic versus neurogenic tone: whereas BK channels and RyRs act in concert to oppose myogenic vasoconstriction, BK channels oppose neurogenic vasoconstriction and RyRs augment it. A scheme for neurogenic vasoregulation is proposed in which RyRs act in conjunction with VDCCs to regulate nerve-evoked constriction in mesenteric resistance arteries.