Role of InsP3and ryanodine receptors in the activation of capacitative Ca2+entry by store depletion or hypoxia in canine pulmonary arterial smooth muscle cells

Open Access
Publisher Website
Google Scholar
Abstract
Background and purpose: Experiments were performed to determine if capacitative Ca2+entry (CCE) in canine pulmonary arterial smooth muscle cells (PASMCs) is dependent on InsP3receptors or ryanodine receptors as induction of CCE is dependent on simultaneous depletion of the functionally separate InsP3‐ and ryanodine‐sensitive sarcoplasmic reticulum (SR) Ca2+stores in these cells.Experimental approach: Myocytes were isolated from canine pulmonary arteries using enzymatic procedures and were used within 8 h of preparation. Measurements of cytosolic Ca2+were made by imaging fura‐2 loaded individual myocytes that were perfused with physiological buffered saline solution with or without Ca2+.Key results: Treating myocytes with 10μM cyclopiazonic acid (CPA), removing extracellular Ca2+, and briefly applying 10 mM caffeine and 10μM 5‐hydroxytryptamine (5‐HT) depleted SR Ca2+stores. Extracellular Ca2+reintroduction caused cytosolic [Ca2+] to elevate above baseline signifying CCE. The InsP3receptor inhibitors 2‐aminobiphenylborate (50‐75μM; 2‐APB) and xestospongin‐C (20μM; XeC) abolished CCE. Yet, CCE was unaffected by 10μM or 300μM ryanodine or 10μM dantrolene, which modify ryanodine receptor activity. Higher dantrolene concentrations (50μM), however, can inhibit both ryanodine receptors and InsP3receptors, did reduce CCE. In contrast, CCE activated by hypoxia was unaffected by XeC (20μM).Conclusions and implications: The results provide evidence that CCE activated by depletion of both InsP3and ryanodine SR Ca2+stores in canine PASMCs is dependent on functional InsP3receptors, whereas the activation of CCE by hypoxia appears to be independent of functional InsP3receptors.British Journal of Pharmacology(2007)152, 101–111; doi:10.1038/sj.bjp.0707357