Effects of the Ca agonist Bay K8644 on 45Ca influx and net Ca uptake into rabbit aortic smooth muscle.
We examined the effects of Bay K8644 and external K+ on isolated rings of rabbit aorta. Previous evidence has suggested that the Ca channel agonist, Bay K8644, preferentially opens the potential-sensitive Ca2+ channels (PSCs) rather than receptor-operated Ca2+ channels (ROCs). Bay K8644 stimulated 45Ca influx, net Ca gain and contractile tension were measured as a function of extracellular K+ concentration. Although Bay K8644 induced little tension at 5 mM K+ (PSS), Ca2+ influx was stimulated from a resting value of 12 mumol X kg-1 X min-1 (0.02 pmol X cm-2 X s-1) to 17 mumol X kg-1 X min-1 while the total Ca content increased by 95 mumol X kg-1. This net Ca gain was reversed by 50 mM caffeine. As the external K+ was increased from 5 to 80 mM, the Bay K8644 stimulation of influx and contraction first increased and then decreased. The data are explained in terms of a calcium entry model consisting of membrane Ca2+ channels in series with a subplasmalemmal barrier consisting of superficial sarcoplasmic reticulum (SR).
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Hwang
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Van Breemen
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000818:Animals; D001011:Aorta / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009543:Nifedipine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits
D007473:Ion Channels; D002110:Caffeine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D011188:Potassium; D002118:Calcium