Function and expression of ryanodine receptors and inositol 1,4,5‐trisphosphate receptors in smooth muscle cells of murine feed arteries and arterioles

Key points • Feed arteries and arterioles, respectively, control the magnitude and distribution of blood flow to skeletal muscle but regional differences in the regulation of vasomotor tone are poorly understood. • To provide this insight, we investigated functional roles and molecular expression of the calcium‐release channels, ryanodine receptors (RyRs) and inositol 1,4,5‐trisphosphate receptors (IP3Rs) in smooth muscle cells (SMCs) of isolated pressurized vessels of mice. • In feed arteries, SMCs displayed localized calcium sparks and more global calcium waves. In arterioles, SMCs exhibited only calcium waves. • Calcium signalling and vasomotor tone were governed by both RyRs and IP3Rs in feed arteries, while only IP3Rs were functional in arterioles. Regional differences were also manifest in the expression profile of RyR isoforms. • This new perspective offers the potential for developing novel strategies to target therapeutic interventions to selective regions of vascular beds. We tested the hypothesis that vasomotor control is differentially regulated between feed arteries and downstream arterioles from the cremaster muscle of C57BL/6 mice. In isolated pressurized arteries, confocal Ca2+ imaging of smooth muscle cells (SMCs) revealed Ca2+ sparks and Ca2+ waves. Ryanodine receptor (RyR) antagonists (ryanodine and tetracaine) inhibited both sparks and waves but increased global Ca2+ and myogenic tone. In arterioles, SMCs exhibited only Ca2+ waves that were insensitive to ryanodine or tetracaine. Pharmacological interventions indicated that RyRs are functionally coupled to large‐conductance, Ca2+‐activated K+ channels (BKCa) in SMCs of arteries, whereas BKCa appear functionally coupled to voltage‐gated Ca2+ channels in SMCs of arterioles. Inositol 1,4,5‐trisphosphate receptor (IP3R) antagonists (xestospongin D or 2‐aminoethoxydiphenyl borate) or a phospholipase C inhibitor (U73122) attenuated Ca2+ waves, global Ca2+ and myogenic tone in arteries and arterioles but had no effect on arterial sparks. Real‐time PCR of isolated SMCs revealed RyR2 as the most abundant isoform transcript; arteries expressed twice the RyR2 but only 65% the RyR3 of arterioles and neither vessel expressed RyR1. Immunofluorescent localisation of RyR protein indicated bright, clustered staining of arterial SMCs in contrast to diffuse staining in arteriolar SMCs. Expression of IP3R transcripts and protein immunofluorescence were similar in SMCs of both vessels with IP3R1>>IP