Mobilization of sarcoplasmic reticulum stores by hypoxia leads to consequent activation of capacitative Ca2+ entry in isolated canine pulmonary arterial smooth muscle cells.
Capacitative Ca2+ entry (CCE) has been speculated to contribute to Ca2+ influx during hypoxic pulmonary vasoconstriction (HPV). The aim of the present study was to directly test if acute hypoxia causes intracellular Ca2+ concentration ([Ca2+]i) rises through CCE in canine pulmonary artery smooth muscle cells (PASMCs). In PASMCs loaded with fura-2, hypoxia produced a transient rise in [Ca2+]i in Ca2+-free solution, indicating Ca2+ release from the intracellular Ca2+ stores. Subsequent addition of 2 mm Ca2+ in hypoxia elicited a sustained rise in [Ca2+]i, which was partially inhibited by 10 microm nisoldipine. The dihydropyridine-insensitive rise in [Ca2+]i was due to increased Ca2+ influx, because it was abolished in Ca2+-free solution and hypoxia was shown to significantly enhance the rate of Mn2+ quench of fura-2 fluorescence. The dihyropyridine-insensitive rise in [Ca2+]i and the increased rate of Mn2+ quench of fura-2 fluorescence were inhibited by 50 microm SKF 96365 and 500 microm Ni2+, but not by 100 microm La3+ or 100 microm Gd3+, exhibiting pharmacological properties characteristic of CCE. In addition, predepletion of the intracellular Ca2+ stores inhibited the rise in [Ca2+]i induced by hypoxia. These results provide the first direct evidence that acute hypoxia, by causing Ca2+ release from the intracellular stores, activates CCE in isolated canine PASMCs, which may contribute to HPV.
Ng
Lih Chyuan
LC
Department of Pharmacology/318, University of Nevada School of Medicine, Reno, NV 89557, USA.
Wilson
Sean M
SM
Hume
Joseph R
JR
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015687:Cell Hypoxia / Q000502:physiology*; D004285:Dogs; D005260:Female; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D015737:Nisoldipine / Q000494:pharmacology; D011651:Pulmonary Artery / Q000166:cytology / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology
D002121:Calcium Channel Blockers; D015737:Nisoldipine; D015759:Ionomycin; D002118:Calcium