ET-1 activates Ca2+ sparks in PASMC: local Ca2+ signaling between inositol trisphosphate and ryanodine receptors.
Ca+ sparks originating from ryanodine receptors (RyRs) are known to cause membrane hyperpolarization and vasorelaxation in systemic arterial myocytes. By contrast, we have found that Ca2+ sparks of pulmonary arterial smooth muscle cells (PASMCs) are associated with membrane depolarization and activated by endothelin-1 (ET-1), a potent vasoconstrictor that mediates/modulates acute and chronic hypoxic pulmonary vasoconstriction. In this study, we characterized the effects of ET-1 on the physical properties of Ca2+ sparks and probed the signal transduction mechanism for spark activation in rat intralobar PASMCs. Application of ET-1 at 0.1-10 nM caused concentration-dependent increases in frequency, duration, and amplitude of Ca2+ sparks. The ET-1-induced increase in spark frequency was inhibited by BQ-123, an ETA-receptor antagonist; by U-73122, a PLC inhibitor; and by xestospongin C and 2-aminoethyl diphenylborate, antagonists of inositol trisphosphate (IP3) receptors (IP3Rs). However, it was unrelated to sarcoplasmic reticulum Ca2+ content, activation of L-type Ca2+ channels, PKC, or cADP ribose. Photorelease of caged-IP3 indicated that Ca2+ release from IP3R could cross-activate RyRs to generate Ca2+ sparks. Immunocytochemistry showed that the distributions of IP3Rs and RyRs were similar in PASMCs. Moreover, inhibition of Ca2+ sparks with ryanodine caused a significant rightward shift in the ET-1 concentration-tension relationship in pulmonary arteries. These results suggest that ET-1 activation of Ca2+ sparks is mediated via the ETA receptor-PLC-IP3 pathway and local Ca2+ cross-signaling between IP3Rs and RyRs; in addition, this novel signaling mechanism contributes significantly to the ET-1-induced vasoconstriction in pulmonary arteries.
Div. of Pulmonary and Critical Care Medicine, Johns Hopkins Asthma and Allergy Center, 5501 Hopkins Bayview Circle, Baltimore, MD 21224, USA.
Wei-Min
WM
Zhang
Kay-Pong
KP
Yip
Mo-Jun
MJ
Lin
Larissa A
LA
Shimoda
Wen-Hong
WH
Li
James S K
JS
Sham
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D002478:Cells, Cultured; D019332:Endothelin-1 / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism; D011651:Pulmonary Artery / Q000166:cytology* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020239:Receptor Cross-Talk / Q000187:drug effects / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D019332:Endothelin-1; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel