PROPERTIES OF A PROTEIN-KINASE C-ACTIVATED CHLORIDE CURRENT IN GUINEA-PIG VENTRICULAR MYOCYTES

Cardiac ventricular myocytes from several species, including the guinea pig, possess a cAMP-dependent protein kinase A (PKA)-activated Cl- channel. In the present study, the properties of a protein kinase C (PKC)-activated Cl- current were studied in isolated guinea pig ventricular myocytes using the whole-cell arrangement of the patch-clamp technique. Intracellular dialysis of ventricular cells with PKC resulted in the activation of a large background current that displayed time-independent kinetics. In the presence of 146 mmol/L external Cl- and 71 mmol/L internal Cl-, the reversal potential (E(rev)) of the background current (-171 +/- 1 mV) was close to that of the Cl- equilibrium potential (-18 mV), and the current versus voltage relation for the current was outward rectifying in shape. When [Cl-](i) or [Cl-](o) was reduced by substitution of Cl- with aspartic acid, E(rev) for the background current shifted in a manner expected for a Cl--selective channel. Based on E(rev) measurements, the permeability sequence for this PKC-activated Cl- channel was determined to be SCN->I->Br(-)similar or equal to Cl-. The PKC-activated Cl- current was not inhibited by the Cl- channel blocker 4,4'-dinitrostilbene-2,2'-disulfonic acid (100 mu mol/L) but could be blocked by anthracene-9-carboxylic acid (1 mmol/L). Activation of the current was abolished in the presence of the PKC inhibitor staurosporine (2.5 mu mol/L). Under conditions designed to cause a maximal activation of the Cl- channels by PKC, the addition of forskolin (1 mu mol/L) to stimulate PKA caused only a slight further increase in the amplitude of the Cl- current. Thus, PKC activates a Cl(-)channel in guinea pig ventricular cells with properties similar but not identical to the PKA-activated channel.