title: Cyclic guanosine monophosphate-enhanced sequestration of Ca2+ by sarcoplasmic reticulum in vascular smooth muscle.
abstract: The purpose of this study was to investigate the effects of the intracellular messenger cyclic GMP (cGMP) on sequestration of cytosolic calcium (Ca2+) into the intracellular Ca2+ store (the sarcoplasmic reticulum) of vascular smooth muscle. Using saponin-skinned primary cultures of rat aortic smooth muscle, we investigated the effect of cGMP on 45Ca uptake in monolayers of cells. The intracellular store was loaded with Ca2+ by exposing the skinned cells to a 45Ca-labeled 1-microM free Ca2+-containing solution for varying durations (0-20 minutes). Addition of 10 microM cGMP to six monolayers increased both the initial Ca2+ uptake at 2 minutes (control, 240 +/- 8 pmol Ca2+/10(6) cells; + cGMP 295 +/- 7; mean +/- SEM; n = 6, p less than 0.01) and the final steady-state uptake reached at 20 minutes (control, 0.96 +/- 0.03 nmol Ca2+/10(6) cells; + cGMP 1.12 +/- 0.03, p less than 0.02). This stimulation of uptake was quantitatively similar to that caused by 10 microM cyclic AMP. It occurred at varying ambient cytosolic Ca2+ concentrations (0.1-1.0 microM Ca2+) and was not further enhanced by addition of 10 microM cGMP-dependent protein kinase. The dose-response of stimulation of Ca2+ uptake with cGMP indicated an ED50 of 5 nM cGMP. The release of Ca2+ from the sarcoplasmic reticulum in response to inositol 1,4,5-trisphosphate or caffeine was unaffected by cGMP. We conclude that the relaxation of vascular smooth muscle with cGMP-producing vasodilators is mediated in part by sequestration of cytosolic Ca2+ by the sarcoplasmic reticulum.
authors.affiliation: Department of Pharmacology, University of Miami School of Medicine, Florida.
authors.forename: C H
authors.initials: CH
authors.lastname: Twort
authors.forename: C
authors.initials: C
authors.lastname: van Breemen
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D006152:Cyclic GMP / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D002110:Caffeine; D006152:Cyclic GMP; D002118:Calcium