A VOLTAGE-SENSITIVE TRANSIENT POTASSIUM CURRENT IN MOUSE PANCREATIC ACINAR-CELLS

We describe, for the first time, a potassium current in acutely isolat ed mouse pancreatic acinar cells. This current is activated by depolar ization and has many of the characteristics of the fast transient pota ssium current of neurones where roles in shaping action potential dura tion and frequency have been proposed. Although acinar cells do not ca rry action potentials, our experiments indicate that the primary regul ator of the current in these cells is the membrane potential. In whole -cell patch-clamped cells we demonstrate an outward current activated by depolarization. This current was transient and inactivated over the duration of the pulse (100-500 ms). The decay of the inactivation was adequately fitted by a single exponential. The time constant of decay , tau, at a membrane potential of +20 mV was 34 +/- 0.6 ms (mean +/- S EM, n = 6) and decreased with more positive pulse potentials. The stea dy-state inactivation kinetics showed that depolarized holding potenti als reduced the amplitude of the current observed with a half-maximal inactivation at a membrane potential of -40.6 +/- 0.33 mV (mean +/- SE M, n = 5). These activation and inactivation characteristics were not affected by low intracellular calcium (10(-10) mol . l(-1)) or by an i ncrease in calcium (up to 180 nmol . l(-1)). In addition we found no e ffect on the current of dibutyryl cyclic adenosine monophosphate (db-c AMP) or the agonist acetylcholine. The current was blocked by 4-aminop yridine (K-d approximately 0.5 mmol . l(-1)) but not affected by 10 mm ol . l(-1) tetraethylammonium. Whole-cell patch-clamp experiments were also carried out on acutely isolated mouse lacrimal acinar cells. Dep olarizing voltage-clamp steps elicited only a slowly activating outwar d current that was blocked by tetraethylammonium. We found no evidence for the fast transient outward current in the exocrine cells of the l acrimal gland. We postulate that the transient potassium current in th e acinar cells of the mouse pancreas would act to hyperpolarize the ce ll and may play a role in fluid secretion.