BACKGROUND AND PURPOSE P2X receptors mediate sympathetic control and autoregulation of the renal circulation triggering contraction of renal vascular smooth muscle cells (RVSMCs) via an elevation of intracellular Ca2+ concentration ([Ca2+]i). Although it is well-appreciated that the myocyte Ca2+ signalling system is composed of microdomains, little is known about the structure of the [Ca2+]i responses induced by P2X receptor stimulation in vascular myocytes.
EXPERIMENTAL APPROACHES Using confocal microscopy, perforated-patch electrical recordings, immuno-/organelle-specific staining, flash photolysis and RT-PCR analysis we explored, at the subcellular level, the Ca2+ signalling system engaged in RVSMCs on stimulation of P2X receptors with the selective agonist αβ-methylene ATP (αβ-meATP).
KEY RESULTS RT-PCR analysis of single RVSMCs showed the presence of genes encoding inositol 1,4,5-trisphosphate receptor type 1(IP3R1) and ryanodine receptor type 2 (RyR2). The amplitude of the [Ca2+]i transients depended on αβ-meATP concentration. Depolarization induced by 10 µmol·L−1αβ-meATP triggered an abrupt Ca2+ release from sub-plasmalemmal (‘junctional’) sarcoplasmic reticulum enriched with IP3Rs but poor in RyRs. Depletion of calcium stores, block of voltage-gated Ca2+ channels (VGCCs) or IP3Rs suppressed the sub-plasmalemmal [Ca2+]i upstroke significantly more than block of RyRs. The effect of calcium store depletion or IP3R inhibition on the sub-plasmalemmal [Ca2+]i upstroke was attenuated following block of VGCCs.
CONCLUSIONS AND IMPLICATIONS Depolarization of RVSMCs following P2X receptor activation induces IP3R-mediated Ca2+ release from sub-plasmalemmal (‘junctional’) sarcoplasmic reticulum, which is activated mainly by Ca2+ influx through VGCCs. This mechanism provides convergence of signalling pathways engaged in electromechanical and pharmacomechanical coupling in renal vascular myocytes.