ATP-SENSITIVE K-MUSCLE FROM COLD-ACCLIMATED GOLDFISH - CHARACTERIZATION AND ALTERED RESPONSE TO ATP( CHANNELS IN CARDIAC)

ATP-sensitive potassium channels (K-ATP) play an important, if incompl etely defined, role in myocardial function in mammals. With the discov ery that K-ATP channels are also present at high densities in the hear ts of vertebrate ectotherms, speculation arises as to their function d uring 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 f rom goldfish (Carassius auratus) acclimated at 7 +/- 1 degrees C relat ive to control (21 +/- 1 degrees C). As previously observed in mammals , K-ATP channels in isolated ventricular myocytes were inwardly rectif ied with slope conductances of 63 pS. However, channel mean open-time and overall open-state probability (P-0) 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 deg rees C. Transmembrane action potential duration (APD) in hearts of col d-acclimated fish studied at 21 degrees was significantly shorter than that observed in hearts of warm-acclimated fish at the same temperatu re; this difference was eliminated by the K-ATP channel antagonist gli benclamide (5 mu M). These data suggest that K-ATP channels in the hea rts of cold-acclimated animals are more active and less sensitive to A TP-inhibition than those in warm-acclimated fish, possibly reflecting a functional adaptation to promote tolerance of low temperatures in th is species. (C) 1998 Elsevier Science Inc.