Changes of membrane currents in cardiac cells induced by long whole-cell recordings and tolbutamide.
Single isolated myocytes were obtained from the ventricles of adult guinea pig hearts. The whole-cell recording configuration of the patch-clamp technique was used to measure membrane currents. A decrease (run-down) of the Ca2+ inward current and an increase of a time-independent K+ outward current were observed during long lasting (1-3h) recordings. The time at which the outward current developed depended on the intracellular ATP concentration in the pipette, suggesting that this current is identical to the ATP-dependent K+ current described by Noma and Shibasaki (1985). However, the maximum outward current reached in the experiments was independent of the ATP concentration indicating a limited diffusion of ATP in the cell interior. In single-channel experiments on isolated patches of cell membrane and in whole-cell recordings the ATP-dependent K+ current could be blocked by the hypoglycaemic sulphonylurea tolbutamide. The IC50 of 0.38 mM was about 50 times higher than that reported for pancreatic beta-cells (Trube et al. 1986). The Ca2+ inward current and the inwardly rectifying K+ current were not affected by tolbutamide (3 mM).
D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D007473:Ion Channels / Q000187:drug effects*; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D014044:Tolbutamide / Q000494:pharmacology*
D007473:Ion Channels; D000255:Adenosine Triphosphate; D014044:Tolbutamide; D011188:Potassium; D002118:Calcium