title: Ca2+ responses of pulmonary arterial myocytes to acute hypoxia require release from ryanodine and inositol trisphosphate receptors in sarcoplasmic reticulum.
abstract: In pulmonary arterial smooth muscle cells (PASMC), acute hypoxia increases intracellular Ca(2+) concentration ([Ca(2+)](i)) by inducing Ca(2+) release from the sarcoplasmic reticulum (SR) and Ca(2+) influx through store- and voltage-operated Ca(2+) channels in sarcolemma. To evaluate the mechanisms of hypoxic Ca(2+) release, we measured [Ca(2+)](i) with fluorescent microscopy in primary cultures of rat distal PASMC. In cells perfused with Ca(2+)-free Krebs Ringer bicarbonate solution (KRBS), brief exposures to caffeine (30 mM) and norepinephrine (300 μM), which activate SR ryanodine and inositol trisphosphate receptors (RyR, IP(3)R), respectively, or 4% O(2) caused rapid transient increases in [Ca(2+)](i), indicating intracellular Ca(2+) release. Preexposure of these cells to caffeine, norepinephrine, or the SR Ca(2+)-ATPase inhibitor cyclopiazonic acid (CPA; 10 μM) blocked subsequent Ca(2+) release to caffeine, norepinephrine, and hypoxia. The RyR antagonist ryanodine (10 μM) blocked Ca(2+) release to caffeine and hypoxia but not norepinephrine. The IP(3)R antagonist xestospongin C (XeC, 0.1 μM) blocked Ca(2+) release to norepinephrine and hypoxia but not caffeine. In PASMC perfused with normal KRBS, acute hypoxia caused a sustained increase in [Ca(2+)](i) that was abolished by ryanodine or XeC. These results suggest that in rat distal PASMC 1) the initial increase in [Ca(2+)](i) induced by hypoxia, as well as the subsequent Ca(2+) influx that sustained this increase, required release of Ca(2+) from both RyR and IP(3)R, and 2) the SR Ca(2+) stores accessed by RyR, IP(3)R, and hypoxia functioned as a common store, which was replenished by a CPA-inhibitable Ca(2+)-ATPase.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, School of Medicine, Baltimore, Maryland, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
authors.forename: Larissa A
authors.initials: LA
authors.lastname: Shimoda
authors.forename: J T
authors.initials: JT
authors.lastname: Sylvester
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015687:Cell Hypoxia; D002478:Cells, Cultured; D007211:Indoles / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047028:Macrocyclic Compounds / Q000494:pharmacology; D008297:Male; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D011651:Pulmonary Artery / Q000166:cytology*; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D007211:Indoles; D053496:Inositol 1,4,5-Trisphosphate Receptors; D047028:Macrocyclic Compounds; D010080:Oxazoles; D019837:Ryanodine Receptor Calcium Release Channel; C511704:xestospongin C; D012433:Ryanodine; D002110:Caffeine; D000252:Calcium-Transporting ATPases; D002118:Calcium; D009638:Norepinephrine; C000543:cyclopiazonic acid