Heterogeneous function of ryanodine receptors, but not IP3 receptors, in hamster cremaster muscle feed arteries and arterioles

Westcott EB, Jackson WE. Heterogeneous function of ryanodine receptors, but not IP3 receptors, in hamster cremaster muscle feed arteries and arterioles. Am J Physiol Heart Circ Physiol 300: H1616-H1630, 2011. First published February 25, 2011; doi:10.1152/ajpheart.00728.2010.-The roles played by ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (IP(3)Rs) in vascular smooth muscle in the microcirculation remain unclear. Therefore, the function of both RyRs and IP(3)Rs in Ca2+ signals and myogenic tone in hamster cremaster muscle feed arteries and downstream arterioles were assessed using confocal imaging and pressure myography. Feed artery vascular smooth muscle displayed Ca2+ sparks and Ca2+ waves, which were inhibited by the RyR antagonists ryanodine (10 mu M) or tetracaine (100 mu M). Despite the inhibition of sparks and waves, ryanodine or tetracaine increased global intracellular Ca2+ and constricted the arteries. The blockade of IP(3)Rs with xestospongin D (5 mu M) or 2-aminoethoxydiphenyl borate (100 mu M) or the inhibition of phospholipase C using U-73122 (10 mu M) also attenuated Ca2+ waves without affecting Ca2+ sparks. Importantly, the IP(3)Rs and phospholipase C antagonists decreased global intracellular Ca2+ and dilated the arteries. In contrast, cremaster arterioles displayed only Ca2+ waves: Ca2+ sparks were not observed, and neither ryanodine (10-50 mu M) nor tetracaine (100 mu M.) affected either Ca2+ signals or arteriolar tone despite the presence of functional RyRs as assessed by responses to the RyR agonist caffeine (10 mM). As in feed arteries, arteriolar Ca2+ waves were attenuated by xestospongin D (5 mu M), 2-aminoethoxydiphenyl borate (100 mu M), and U-73122 (10 mu M), accompanied by decreased global intracellular Ca2+ and vasodilation. These findings highlight the contrasting roles played by RyRs and IP(3)Rs in Ca2+ signals and myogenic tone in feed arteries and demonstrate important differences in the function of RyRs between feed arteries and downstream arterioles.