EFFECTS OF STILBENEDISULFONIC ACID-DERIVATIVES ON THE CAMP-REGULATED CHLORIDE CURRENT IN CARDIAC MYOCYTES

Stilbenedisulfonic acid derivatives have been shown to block Cl- channels directly in many different preparations. Therefore, the utility of these compounds as tools for studying the cAMP-dependent Cl- current (I(Cl)) in guinea-pig ventricular myocytes was examined using the patch-clamp technique to record whole-cell Cl- currents at room temperature. It was found that 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) increased, rather than decreased, the isoproterenol (ISO)-activated Cl- current. However, SITS alone stimulated little or no sustained current, suggesting that SITS activates the Cl- current through a synergistic effect with ISO. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) also enhanced the ISO-activated Cl- current. However, 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS) did not have any effect. SITS also exhibited a synergistic effect on the ISO-enhanced Ca2+ current in the same cells, suggesting that it affects the pathway involved in beta-adrenergic regulation of both Cl- and Ca2+ channels. SITS had no effect on the Cl- current stimulated by direct activation of adenylate cyclase with forskolin or exposure to the membrane-permeable cAMP derivative 8-bromoadenosine 3',5'-cyclic monophosphate. This suggests that SITS and DIDS may enhance the ISO-activated Cl- current via an effect on the beta-adrenergic receptor. It is concluded that these stilbenedisulfonic acid derivatives are not effective antagonists of cAMP-activated Cl- channels in cardiac ventricular myocytes.