Swelling-induced Cl- current in guinea-pig atrial myocytes:: inhibition by glibenclamide

1. Whole-cell currents were recorded from guinea-pig atrial myocytes using the patch-clamp technique under conditions designed to block K+ channels, Ca2+ channels and electrogenic transporters. 2. Exposure of atrial myocytes to the hyposmotic external solution (Na+ reduction to about 70% of control) resulted in hyposmotic cell swelling which was associated with activation of an outwardly rectifying Cl- current (I-Cl,I-swell). 3. Whereas the activation of I-Cl,I-swell was not significantly affected by replacement of ATP in the pipette solution with the non-hydrolysable ATP analogue 5'-adenylyl-imidodiphosphate (AMP-PNP), its activation was greatly reduced in cells dialysed with an ATP-free pipette solution, thus indicating that the activation process of I-Cl,I-swell requires the presence of intracellular ATP, but not its hydrolysis. 4. Bath application of glibenclamide produced a concentration-dependent block of I-Cl,I-swell with a half-maximal inhibitory concentration (IC50) of 60.0 mu M and a Hill coefficient of 2.1. The maximal effect (100% inhibition) was obtained with 500 mu M glibenclamide. The steady-state inhibition showed little voltage dependence, while glibenclamide at concentrations of more than 100 mu M inhibited the outward I-Cl,I-swell more rapidly than the inward I-Cl,I-swell. The glibenclamide inhibition was fully reversible after removal of the drug, even when a maximal effect (full inhibition) was achieved at a high drug concentration (500 mu M). 5. These results show that (i) glibenclamide is one of the most potent inhibitors of guinea-pig atrial I-Cl,I-swell and (ii) atrial I-Cl,I-swell and the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- currents are almost equally sensitive to inhibition by glibenclamide.