Requirement of Ryanodine Receptor Subtypes 1 and 2 for Ca super(2+)-induced Ca super(2+) Release in Vascular Myocytes

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 (Ca super(2+) sparks) and global Ca super(2+) 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 Ca super(2+) measurements revealed that depolarization-induced Ca super(2+) sparks and global Ca super(2+) responses were blocked when either RYR1 or RYR2 expression was suppressed. Caffeine-induced Ca super(2+) 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 Ca super(2+) responses. Our results show that, in vascular myocytes, the two RYR1 and RYR2 subtypes are required for Ca super(2+) release during Ca super(2+) sparks and global Ca super(2+) responses, evoked by activation of voltage-gated Ca super(2+ )channels.