The effect of forskolin on sodium current (INa) was studied in enzymatically dispersed frog atrial myocytes. The single pipette patch-clamp technique was used, with a low external sodium concentration. Forskolin (0.5 microM) increased INa at all potentials between -50 and +30 mV. The forskolin-induced increase of INa was mimicked by 1,9-dideoxyforskolin (0.5 microM) but not by isoprenaline (2 microM). These results suggest that forskolin can modulate INa through a mechanism that does not involve the production of cyclic AMP.