MODULATION OF L-TYPE CA CHANNEL ACTIVITY BY P-2-PURINERGIC AGONIST IN CARDIAC-CELLS

The mechanism of enhancement of the L-type Ca current by a P2-purinergic agonist adenosine-5'-O-(3-thiotriphosphate) (ATPgammaS) was studied by recording single channel activity from cell-attached patches on rat isolated ventricular cells using patch pipettes containing 110 mM Ba2+. The application of ATPgammaS to the patch membrane through the pipette solution did not affect single channel activity. The addition of ATPgammaS to the bath containing a depolarizing solution was ineffective due to the voltage dependence of the purinergic stimulation. Bath application of ATPgammaS (100 muM) to control 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid (HEPES) solution increased the amplitude of ensemble average currents both by decreasing the probability of a blank sweep occurring and by increasing the number of openings per non-blank sweep. The single channel conductance (17 pS) was not changed by ATPgammaS. Both activation and inactivation curves were shifted towards hyperpolarized potentials by about 10 mV under P2-purinergic stimulation. Since ATPgammaS increased channel activity when applied via the bath, it must be supposed that a diffusible messenger is involved.