To gain some insight into electrogenic transport processes across the plasma membrane of Madin-Darby canine kidney (MDCK)-cells, continuous measurements of the potential difference across the plasma measurements of the potential difference across the plasma membrane (PD) were made during step changes of extracellular ion composition as well as application of barium or valinomycin. During control conditions mimicking in vivo extracellular fluid, PD approaches -51.5 +/- 0.8 mV (n = 62). Step increase of extracellular potassium concentration from 5.4 to 10, to 20 or to 35 mmol/l, depolarizes PD by +5.5 +/- 0.8 mV (n = 7), by +15.8 +/- 0.5 mV (n = 64) and by +23.8 +/- 1.2 mV (n = 12), respectively. 1 mmol/l barium depolarizes PD by +19.8 +/- 0.6 mV (n = 38) and abolishes the effect of increasing extracellular potassium from 5.4 to 10 mmol/l but not to 35 mmol/l. Ten mumol/l valinomycin hyperpolarizes PD to -69.3 +/- 2.9 mV (n = 7). In the presence of valinomycin, increase of extracellular potassium from 5.4 to 20 mmol/l depolarizes PD by +31.0 +/- 1.0 mV (n = 7). Ouabain depolarizes PD and reduces the sensitivity of PD to extracellular potassium concentration. Omission of extracellular bicarbonate and carbon dioxide as well as increase of extracellular bicarbonate at constant carbon dioxide lead to a hyperpolarization and enhanced sensitivity of PD to extracellular potassium. In the presence of barium, the effects of omitted bicarbonate and carbon dioxide of MDCK-cells is highly conductive to potassium.(ABSTRACT TRUNCATED AT 250 WORDS)