Gating properties of ATP-sensitive K+ channels in the heart

Using a concentration jump technique (oil-gate method), the rate of closure or opening of the ATP-sensitive K+ channel was measured in response to varying the ATP concentration. The inside-out patch was prepared from dissociated ventricular cells of guinea-pig heart. The opening of the channel on jump to ATP-free solutions from various ATP concentrations showed a variable latent period before the almost exponential rise of the mean channel current. The mechanism of latency is not clear. On reapplying ATP, the channel closed without any obvious delay, and the time course was well fitted with a single exponential curve. The reciprocal time constant was proportional to the ATP concentration. The closing rate was explained by assuming a 1:1 binding stoichiometry and a rate constant of 51.7 or 5.6 mM-1s-1.