Mechanism for reactivation of the ATP‐sensitive K+ channel by MgATP complexes in guinea‐pig ventricular myocytes.

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Abstract
1. A mechanism underlying reactivation of the adenosine 5'‐triphosphate‐sensitive K+ (K+ATP) channels by MgATP complexes after run‐down was examined in guinea‐pig ventricular myocytes using the patch‐clamp technique with inside‐out patch configuration. 2. After run‐down was induced by exposure of the intracellular side of the membrane patch to Ca2+ (1 mM), channel activity was reactivated by exposure and subsequent wash‐out of MgATP (2 mM). Addition of inhibitors of various serine/threonine protein kinases to the MgATP solution did not suppress reactivation of the run‐down channels. 3. Non‐ or poorly hydrolysable ATP analogues were unable to reactivate run‐down channels. 4. The degree of channel recovery was dependent upon the duration of MgATP exposure. The apparent half‐activation value (K1/2) of MgATP for reactivation was decreased with increasing exposure time. 5. Various products of ATP hydrolysis were unable to reactivate run‐down channels except a relatively low concentration (100 microM) of ADP exposure. 6. Other nucleotide triphosphates, in the presence of Mg2+, were unable to reactivate rundown channels. 7. Fluorescein 5‐isothiocyanate (50 microM), which interacts with lysine residues of the nucleotide‐binding site on various ATPases, inhibited K+ATP channel activity. After wash‐out, channel activity recovered only slightly. 8. These data suggest that the hydrolysis of ATP is important for reactivation of run‐down K+ATP channels but that protein phosphorylation by serine/threonine protein kinases may not be involved. Since no products of ATP hydrolysis could reproduce MgATP‐induced channel reactivation and since the degree of channel recovery was dependent upon the duration of MgATP application, the hydrolysis energy appears to be utilized for channel reactivation.