FUNCTIONAL INTERACTION BETWEEN K-ATP CHANNELS AND THE NA-K+ PUMP IN METABOLICALLY INHIBITED HEART-CELLS OF THE GUINEA-PIG()

1. Transmembrane current through ATP-regulated K+ channels (I-K(ATP)) was measured in ventricular heart cells of the guinea-pig in the whole -cell and cell-attached patch configurations under conditions of metab olic poisoning with the mitochondrial uncoupler 2,4-dinitrophenol (DNP ). 2. Maintained exposure of the cells to DNP resulted in a transient appearance of whole-cell I-K(ATP). When I-K(ATP) had reached several n anoamps, blocking the forward-running Na+-K+ pump with 0.5 mM strophan thidin decreased I-K(ATP) after a delay. The time course of this decre ase could be described by a single exponential function, which yielded a time constant (tau) of 4.51 +/- 1.89 s (n = 8). 3. Hyperpolarizatio n from 0 mV to -100 or -150 mV for 2 s caused I-K(ATP) (measured at 0 mV) to decrease by 34.2 +/- 14.1% (n = 8) and 37.6 +/- 9.4% (n = 8), r espectively. After the hyperpolarizing pulse, I-K(ATP) returned to its higher initial level within a couple of seconds. 4. Driving the pump backwards by removing the extracellular Kf ions caused the permanent d isappearance of DNP-induced I-K(ATP). 5. Application of 0.5 mM stropha nthidin in the absence of external Kf ions induced a transient increas e in I-K(ATP) as did washing out the glycoside (n = 5). 6. When pump a ction was inhibited by using Na+, K+-free Tyrode solution (see Methods ) in the bath, strophanthidin did not have a comparable direct effect on I-K(ATP). 7. In cell-attached patches, strophanthidin applied via t he bath caused a reduction in I-K(ATP) with a similar time course to t hat in whole-cell experiments. This suggests that the interaction betw een the pump molecules and the K-ATP channels is not restricted to clo sely neighbouring molecules. 8. The data support the hypothesis that [ ATP] at the cytosolic face of the membrane may drop to practically zer o, thereby passing an 'ATP window' in which the channels first open an d then close, and that the submembrane [ATP] is readily controlled by the cytosolic [ATP].