Effect of bradykinin, ATP and adrenaline on cell membrane resistances of Madin-Darby canine kidney cells.

1. Previous studies have shown that bradykinin, ATP and adrenaline hyperpolarize the cell membrane of Madin-Darby canine kidney (MDCK) cells by activation of calcium-sensitive K+ channels. The present study has been performed to determine the effect of these hormones on the resistance of the cell membrane and the cellular coupling. To this end, cellular cable analysis has been performed. 2. As a result, all three hormones lead to the expected, marked decrease of cell membrane resistance. 3. However, the bradykinin-induced reduction of cell membrane resistance was sustained, contrasting with only transient hyperpolarization induced by bradykinin and only transient activation of the K+ channels. Thus, the cable analysis reveals the sustained activation of an additional conductance. 4. ATP, but not the other two hormones, leads to a delayed increase of the intercellular coupling resistances. 5. Prolonged exposure of the cells to adrenaline leads to oscillations of the cell membrane potential, apparently by oscillatory activation of the K+ channels.