Genetic evidence for functional role of ryanodine receptor 1 in pulmonary artery smooth muscle cells

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Abstract
Ryanodine receptor 1 (RyR1) is well-known to be expressed in systemic and pulmonary vascular smooth muscle cells (SMCs); however, its functional roles remain largely unknown. In the present study, we attempted to determine the potential importance of RyR1 in membrane depolarization-, neurotransmitter-, and hypoxia-induced Ca2+ release and contraction in pulmonary artery SMCs (PASMCs) using RyR1 homozygous and heterozygous gene deletion (RyR1−/− and RyR1+/−) mice. Our results indicate that spontaneous local Ca2+ release and caffeine-induced global Ca2+ release are significantly reduced in embryonic RyR1−/− and adult RyR+/− cells. An increase in [Ca2+]i following membrane depolarization with high K+ is markedly attenuated in RyR1−/− and RyR1+/− PASMCs in normal Ca2+ or Ca2+-free extracellular solution. Similarly, muscle contraction evoked by membrane depolarization is reduced in RyR1+/− pulmonary arteries in the presence or absence of extracellular Ca2+. Neurotransmitter receptor agonists and inositol 1,4,5-triphosphate elicit a much smaller increase in [Ca2+]i in both RyR1−/− and RyR1+/− cells. We have also found that neurotransmitter-evoked muscle contraction is significantly inhibited in RyR1+/− pulmonary arteries. Hypoxia-induced increase in [Ca2+]i and contraction are largely blocked in RyR1−/− and/or RyR1+/− PASMCs. Collectively, our findings provide genetic evidence for the functional importance of RyR1 in spontaneous local Ca2+ release, and membrane depolarization-, neurotransmitter-, as well as hypoxia-induced global Ca2+ release and attendant contraction in PASMCs.

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