ACTIVATION OF ATP-DEPENDENT K+ CHANNELS BY METABOLIC POISONING IN ADULT-MOUSE SKELETAL-MUSCLE - ROLE OF INTRACELLULAR MG2+ AND PH

1. The effects of metabolic poisoning, intracellular Mg2+ and pH on ATP-dependent K+ (K-ATP(+)) channels were examined in adult mouse isolated skeletal muscle fibres using the patch clamp technique. 2. In cell-attached membrane patches, while openings of one kind of channel could only rarely be detected under control conditions, cell poisoning with fluorodinitrobenzene (FDNB), dinitrophenol (DNP) and cyanide (CN) induced a strong and partially reversible increase in channel activity. 3. Slope conductance and glibenclamide sensitivity of this outward current indicated that the channel activated during poisoning mas the K-ATP(+) channel. 4. Single channel current amplitude was reduced during poisoning, but remained unchanged when activation of the K-ATP(+) channel was induced by cromakalim. 5. In inside-out membrane patches, in the absence of intracellular ATP, intracellular application of Mg2+ decreased channel activity and single channel current amplitude. Inhibition of K-ATP(+) channels by ATP was also reduced. 6. In the absence of intracellular ATP, a decrease in intracellular pH induced a reduction in channel activity and single channel current amplitude. Inhibition of K-ATP(+) channels by ATP was also reduced. 7. The reduction of single channel current amplitude during poisoning was attributed to an increase in intracellular Mg2+ concentration caused by a fall in intracellular ATP concentration. These results also show that metabolic poisoning causes direct activation of K-ATP(+) channels in skeletal muscle, and that this activation is at least partially mediated through an increase in intracellular Mg2+ concentration and a decrease in intracellular pH.