Li+ inhibition of membrane current responses to epinephrine in guinea-pig ventricular cells

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Abstract
Membrane currents of guinea-pig ventricular myocytes were recorded using the whole-cell voltage clamp method. The epinephrine-induced increase in Ca2+ current (2.9±0.5 times control) was reduced (1.8 ±0.3 times) by replacing Na+ with Li+ in the bathing solution. In addition, 0.5 μ M epinephrine increased a time-independent membrane conductance in the Na+ external solution, having a reversal potential of −19 ±3 mV (epinephrine-induced current). In the Li+ external solution, however, 0.5 μ M epinephrine failed to induce the epinephrine-induced current. The findings are consistent with the reported Li+ inhibition of GTP-binding protein and/or adenylate cyclase.