Enhanced cardiac KATP channel activity after acclimation to hypoxia in goldfish (Carassius auratus L.)

Abstract

Freshwater fishes of the genus Carassius are known for their capacity to survive environmental hypoxia. Further, individual animals may exhibit enhanced tolerance of low oxygen in response to prior acclimation. It has been suggested that the hypoxia‐induced activation of ATP‐sensitive potassium (KATP) channels in critical tissues serves a protective role, increasing tolerance of low oxygen. In goldfish, we have previously shown that mRNA transcription of genes relevant to cardiac KATP channel structure and regulation are altered in response to acclimation under moderately hypoxic conditions (2.6 mg O2/l for seven days at 22°C). In the present study, we used standard intracellular and patch clamp recording techniques to investigate the possibility that this altered transcription is accompanied by functional changes that increase overall KATP channels activity. Intracellular action potential duration in excised ventricles from hypoxia‐acclimated animals was significantly (p<0.05) reduced at both 50% and 90% of full repolarization relative to those from normoxia‐acclimated fish. In cell‐attached ventricular membrane patches from hypoxia‐acclimated goldfish, sarcolemmal KATP channel open probability (NPo) was significantly (p<0.05) enhanced vs. control. These data indicate that prior whole‐animal acclimation to moderate hypoxia enhances overall cardiac KATP channel activity in this species.