ATP-sensitive K+ channels in cardiac muscle from cold-acclimated goldfish: characterization and altered response to...

ATP-sensitive potassium channels (K(ATP)) play an important, if incompletely defined, role in myocardial function in mammals. With the discovery that K(ATP) channels are also present at high densities in the hearts of vertebrate ectotherms, speculation arises as to their function during periods of cold-acclimation and depressed ATP synthesis. We used single-channel and intracellular recording techniques to examine the possibility that channel activity would be altered in cardiac muscle from goldfish (Carassius auratus) acclimated at 7+/-1 degrees C relative to control (21+/-1 degrees C). As previously observed in mammals, K(ATP) channels in isolated ventricular myocytes were inwardly rectified with slope conductances of 63 pS. However, channel mean open-time and overall open-state probability (Po) were significantly increased in cells from the cold-acclimated animals. In addition, K(ATP) channels in cells from fish acclimated at 7 degrees were nearly insensitive to the inhibitory effects of 2 mM ATP, whether studied at 7 or at 21 degrees C. Transmembrane action potential duration (APD) in hearts of cold-acclimated fish studied at 21 degrees was significantly shorter than that observed in hearts of warm-acclimated fish at the same temperature; this difference was eliminated by the K(ATP) channel antagonist glibenclamide (5 microM). These data suggest that K(ATP) channels in the hearts of cold-acclimated animals are more active and less sensitive to ATP-inhibition than those in warm-acclimated fish, possibly reflecting a functional adaptation to promote tolerance of low temperatures in this species.