ATP-sensitive potassium channels and cardiac protection (part 9)
The electric current flowing through ATP-dependent channels has been studied mostly in isolated cardiac cells (single channel or whole cell current recording). Figure 2 illustrates typical single channel recordings in the absence and in the presence of ATP, as well as the effect of a KATP channel opener and inhibitor . The proximity of Katp current reversal potential to the potassium equilibrium potential indicates high selectivity of the channel for K+. At its maximum (at 150 mM extracellular K+), the channel has a remarkably high conductance, up to 78 pS .The characteristic feature of isolated Katp channels is long bursts of activity interrupted by periods of silence. ATP shortens the time of individual bursts and prolongs the periods of silence. The gating mechanism is not yet fully understood. It appears to be quite complex, and the existence of several open and closed states has been proposed .
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Figure 2 Effects of ATP concentration, nicorandil and glibenclamide on the single ATP-sensitive channel current. In the absence of ATP the channel is mostly in the open state (O). Intracellular ATP (0.5 mM) decreases the open state probability. After the addition of the channel opener nicorandil, the rate of openings increases. Subsequent application of Katp channel inhibitor glibenclamide induces almost complete closed state (C). Reproduced by permission from reference 37