Opening of cardiac sarcolemmal KATP channels by dinitrophenol separate from metabolic inhibition

Opening of ATP-sensitive K+ (KATP) channels by the uncoupler of oxidative phosphorylation, 2,4 dinitrophenol (DNP), has been assumed to be secondary to metabolic inhibition and reduced intracellular ATP levels. Herein, we present data which show that DNP (200 microM) can induce opening of cardiac KATP channels, under whole-cell and inside-out conditions, despite millimolar concentrations of ATP (1-2. 5 mm). DNP-induced currents had a single channel conductance (71 pS), inward rectification, reversal potential, and intraburst kinetic properties (open time constant, tauopen: 4.8 msec; fast closed time constant, tauclosed(f): 0.33 msec) characteristic of KATP channels suggesting that DNP did not affect the pore region of the channel, but may have altered the functional coupling of the ATP-dependent channel gating. A DNP analogue, with the pH-titrable hydroxyl replaced by a methyl group, could not open KATP channels. The pH-dependence of the effect of DNP on channel opening under whole-cell, cell-attached, and inside-out conditions suggested that transfer of protonated DNP across the sarcolemma is essential for activation of KATP channels in the presence of ATP. We conclude that the use of DNP for metabolic stress-induced KATP channel opening should be reevaluated.