Role of InsP3 and ryanodine receptors in the activation of capacitative Ca2+ entry by store depletion or hypoxia in canine pulmonary arterial smooth muscle cells.
OBJECTIVE
Experiments were performed to determine if capacitative Ca(2+) entry (CCE) in canine pulmonary arterial smooth muscle cells (PASMCs) is dependent on InsP(3) receptors or ryanodine receptors as induction of CCE is dependent on simultaneous depletion of the functionally separate InsP(3)- and ryanodine-sensitive sarcoplasmic reticulum (SR) Ca(2+) stores in these cells.


METHODS
Myocytes were isolated from canine pulmonary arteries using enzymatic procedures and were used within 8 h of preparation. Measurements of cytosolic Ca(2+) were made by imaging fura-2 loaded individual myocytes that were perfused with physiological buffered saline solution with or without Ca(2+).


RESULTS
Treating myocytes with 10 microM cyclopiazonic acid (CPA), removing extracellular Ca(2+), and briefly applying 10 mM caffeine and 10 microM 5-hydroxytryptamine (5-HT) depleted SR Ca(2+) stores. Extracellular Ca(2+) reintroduction caused cytosolic [Ca(2+)] to elevate above baseline signifying CCE. The InsP(3) receptor inhibitors 2-aminobiphenylborate (50-75 microM; 2-APB) and xestospongin-C (20 microM; XeC) abolished CCE. Yet, CCE was unaffected by 10 microM or 300 microM ryanodine or 10 microM dantrolene, which modify ryanodine receptor activity. Higher dantrolene concentrations (50 microM), however, can inhibit both ryanodine receptors and InsP(3) receptors, did reduce CCE. In contrast, CCE activated by hypoxia was unaffected by XeC (20 microM).


CONCLUSIONS
The results provide evidence that CCE activated by depletion of both InsP(3) and ryanodine SR Ca(2+) stores in canine PASMCs is dependent on functional InsP(3) receptors, whereas the activation of CCE by hypoxia appears to be independent of functional InsP(3) receptors.
Ng
L C
LC
Department of Pharmacology, University of Nevada School of Medicine, Reno, NV, USA.
Wilson
S M
SM
McAllister
C E
CE
Hume
J R
JR
D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015687:Cell Hypoxia; D003600:Cytosol / Q000378:metabolism; D003620:Dantrolene / Q000494:pharmacology; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047028:Macrocyclic Compounds / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010080:Oxazoles / Q000494:pharmacology; D011651:Pulmonary Artery / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology; D013997:Time Factors
D001896:Boron Compounds; D004791:Enzyme Inhibitors; 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; D012701:Serotonin; D002110:Caffeine; C109986:2-aminoethoxydiphenyl borate; D000252:Calcium-Transporting ATPases; D003620:Dantrolene; D002118:Calcium; C000543:cyclopiazonic acid