Voltage-dependent effects of isoproterenol on cytosolic Ca concentration in rat heart.
The effect of the beta-adrenoceptor agonist, isoproterenol, on cytosolic calcium concentration ([Ca2+]i) was studied with the Ca2+-sensitive fluorescent indicator quin 2 in enzymatically dissociated rat ventricular myocytes. Under conditions in which cells have normal polarized resting membrane potential, isoproterenol (1 microM) produced a decrease in [Ca2+]i. In contrast, in the depolarized cells (by raising extracellular K+ concentration to 50 mM), isoproterenol (1 microM) caused an increase in [Ca2+]i. This isoproterenol-induced increase in [Ca2+]i in depolarized cells could be reversed by prior exposure of the cells to the Ca2+ channel blocker, verapamil (5 microM). The results indicate that isoproterenol can either decrease or increase [Ca2+]i depending on membrane potential. The actual effect of isoproterenol on [Ca2+]i at any given membrane potential probably reflects the relative contributions of isoproterenol-induced stimulation of Ca2+ buffering or effluxing activities (which favor a decrease in [Ca2+]i) and enhancement of Ca2+ influx through voltage-sensitive Ca2+ channels (which favors an increase in [Ca2+]i).
D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology*; D008564:Membrane Potentials; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000502:physiology
D000634:Aminoquinolines; D007473:Ion Channels; D011943:Receptors, Adrenergic, beta; D011189:Potassium Chloride; C035738:Quin2-acetoxymethyl ester; D011433:Propranolol; D007545:Isoproterenol; D002118:Calcium