Effects of bradykinin on electrical properties of Madin-Darby canine kidney epithelioid cells

In the present study we have investigated the influence of bradykinin on the potential difference across the cell membrane (PD) of Madin Darby Canine Kidney (MDCK)-cells. In the absence of bradykinin PD averages –52.6±0.9 mV (n=52). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +5.2±0.3 mV (n=8) and +14.9±1.0 mV (n=9), respectively. The application of 0.1 mol/l bradykinin leads to a transient hyperpolarization of the cell membrane to –70.3±0.6 mV (n=30). During this transient hyperpolarization increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +10.4±0.7 mV (n=10) and +29.2±0.8 mV (n=8) respectively. Application of fragments of bradykinin (0.1 mol/l) are without significant effect on the potential difference across the cell membrane. 1 mmol/l barium depolarizes the cell membrane by +15.8±1.2 mV (n=9) and abolishes the effect of step increase of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, bradykinin leads to a transient hyperpolarization by –24.7±1.3 mV (n=7). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. In the nominal absence of extracellular calcium, bradykinin leads to a transient hyperpolarization, which can be elicited only once. The transient hyperpolarization is not affected by the presence of verapamil or indomethacin. In conclusion, bradykinin hyperpolarizes MDCK-cells by increasing the apparent potassium conductance. This effect is probably mediated by increase of intracellular calcium activity.