Beta-adrenergic modulation in the heart. Independent regulation of K and Ca channels.

The temperature-dependence of the actions of beta-receptor agonists and adenylate cyclase stimulation on both calcium and delayed rectifier potassium channel ionic currents were examined in patch-clamped guinea pig ventricular myocytes. We report that temperature can separate the beta-receptor mediated modulation of potassium and calcium channels. Receptor-mediated increases in the delayed rectifier potassium current, but not the calcium current were very temperature-dependent over the range of 19 to 32 degrees C. At room temperature (19-22 degrees C) the beta-agonist isoproterenol produced a large enhancement of the calcium current but had no effect on the delayed rectifier current. In contrast, at warmer temperatures (28-32 degrees C) both currents increased in the presence of the agonist. This temperature-sensitivity also existed for direct stimulation of adenylate cyclase by forskolin. Thus, cardiac calcium and potassium channels appear to be independently regulated during adrenergic stimulation.