Negative regulation of cellular Ca2+mobilization by ryanodine receptor type 3 in mouse mesenteric artery smooth muscle

Physiological functions of type 3 ryanodine receptors (RyR3) in smooth muscle (SM) tissues are not well understood, in spite of their wide expression. However, the short isoform of RyR3 is known to be a dominant-negative variant (DN-RyR3), which may negatively regulate functions of both RyR2 and full-length (FL) RyR3 by forming hetero-tetramers. Here, functional roles of RyR3 in the regulation of Ca 2+ signaling in mesenteric artery SM cells (MASMCs) were examined using RyR3 homozygous knockout mice (RyR3 −/− ). Quantitative PCR analyses suggested that the predominant RyR3 subtype in MASMs from wild-type mice (RyR3 +/+ ) was DN-RyR3. In single MASMCs freshly isolated from RyR3 −/− , the EC 50 of caffeine to induce Ca 2+ release was lower than that in RyR3 +/+ myocytes. The amplitude and frequency of Ca 2+ sparks and spontaneous transient outward currents in MASMCs from RyR3 −/− were all larger than those from RyR3 +/+ . Importantly, mRNA and functional expressions of voltage-dependent Ca 2+ channel and large-conductance Ca 2+ -activated K + (BK) channel in MASMCs from RyR3 −/− were identical to those from RyR3 +/+ . However, in the presence of BK channel inhibitor, paxilline, the pressure rises induced by BayK8644 in MA vascular beds of RyR3 −/− were significantly larger than in those of RyR3 +/+ . This indicates that the negative feedback effects of BK channel activity on intracellular Ca 2+ signaling was enhanced in RyR3 −/− . Thus, RyR3, and, in fact, mainly DN-RyR3, via a complex with RyR2 suppresses Ca 2+ release and indirectly regulated membrane potential by reducing BK channel activity in MASMCs and presumably can affect the regulation of intrinsic vascular tone.