The effects of the Ca2+-channel activator BAY K 8644 (a novel dihydropyridine) on transepithelial potential difference (Pd), electrical resistance (Rt), and unidirectional Na+-fluxes were studied in the rabbit gall-bladder. It was observed that BAY K 8644 at concentrations between 10(-7) and 10(-5) M induced regular oscillations in the transepithelial Pd, without affecting the mean value of Pd (or Rt). The mean oscillatory frequency was 18 mHz (approximately 1 cycle per min), and the mean amplitude was 30-35 microV. Oscillations were predominantly elicited from the serosal side. 10(-5) M BAY K 8644 reduced net Na+ -absorption by 16% by inhibiting the mucosa-to-serosa flux. Nifedipine blocked the Pd-oscillations but did not reverse the Na+-transport inhibition. The observed effects of BAY K 8644 are consistent with activation of Ca2+-channels and an increase in intracellular Ca2+-concentration.