Requirement of ryanodine receptor subtypes 1 and 2 for Ca2+-induced Ca2+ release in vascular myocytes

Abstract

While the roles of subtypes 1 and 2 of the ryanodine receptors (RYRs) have been studied in cellular systems expressing specifically one or the other of these subtypes (i.e. skeletal and cardiac muscle), the function of these receptors has not been evaluated in smooth muscles. We have previously reported RYR-mediated elementary (Ca2+ sparks) and global Ca2+ responses in rat portal vein myocytes. Here, we investigated the respective roles of all three RYR subtypes expressed in these cells as revealed by reverse transcriptase-polymerase chain reaction. Antisense oligonucleotides targeting each one of the three RYR subtypes were shown to specifically inhibit the expression of the corresponding mRNA and protein without affecting the other RYR subtypes. Confocal Ca2+ measurements revealed that depolarization- induced Ca2+ sparks and global Ca2+ responses were blocked when either RYR1 or RYR2 expression was suppressed. Caffeine-induced Ca2+ responses were partly inhibited by the same antisense oligonucleotides. Neither the corresponding scrambled oligonucleotides nor the antisense oligonucleotides targeting RYR3 affected depolarization- or caffeine-induced Ca2+ responses. Our results show that, in vascular myocytes, the two RYR1 and RYR2 subtypes are required for Ca2+ release during Ca2+ sparks and global Ca2+ responses, evoked by activation of voltage-gated Ca2+ channels.