title: Vasopressin-evoked [Ca2+]i responses in neonatal rat cardiomyocytes.
abstract: The presence of arginine vasopressin (AVP) V1 receptors on neonatal rat cardiomyocytes (NRCs) linked to processes capable of elevating intracellular free calcium ([Ca2+]i) is now firmly established. This study examined the sources and signaling involved in [Ca2+]i elevations evoked by AVP in NRCs. AVP promoted increases in both [Ca2+]i and 1,4,5-inositoltrisphosphate (IP3) levels in NRCs. The degree of [Ca2+]i elevation was less than that of angiotensin II, but greater than that of endothelin-1. Extracellular Mg2+ depletion led to diminution of the maximal [Ca2+]i response, with a rightward shift in the concentration-response curves to AVP. The phospholipase C inhibitors, D-609, NCDC, or U73122, and the IP3 receptor blocker, heparin, abolished the [Ca2+]i response to AVP. Neither cyclooxygenase inhibition with indomethacin nor PKC inhibition with staurosporine had any effect. Neither ryanodine nor caffeine, which deplete sarcoplasmic reticulum (SR) Ca2+ stores, nor ruthenium red, which inhibits both SR and mitochondrial Ca2+ stores, affected [Ca2+]i responses to AVP. The SR Ca2+ pump inhibitor, cyclopiazonic acid, abolished, and removal of extracellular Ca2+ attenuated, the response to AVP. These data indicate that activation of cardiac V1 receptors by AVP results in mobilization of Ca2+ from a distinct, non-SR, nonmitochondrial, intracellular Ca2+ pool that is Ca2+ pump replenished and IP3 sensitive. This process occurs secondary to phospholipase C (PLC)-mediated generation of IP3, requires the presence of Mg2+ and extracellular Ca2+, and occurs in a manner independent of PKC and cyclooxygenase activation. Such mechanisms of Ca2+ mobilization might indicate a distinct role for AVP in cardiac physiology and disease.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Liu
authors.forename: R L
authors.initials: RL
authors.lastname: Hopfner
authors.forename: Y J
authors.initials: YJ
authors.lastname: Xu
authors.forename: V
authors.initials: V
authors.lastname: Gopalakrishnan
mesh_terms: D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001127:Arginine Vasopressin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004347:Drug Interactions; D016232:Endothelins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006321:Heart / Q000187:drug effects*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D016232:Endothelins; D004791:Enzyme Inhibitors; D000804:Angiotensin II; D001127:Arginine Vasopressin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium