ABSTRACT
ATP-sensitive potassium channels (KATP) were discovered by Noma (1983) in the cardiac myocyte. These channels are modulated by intracellular ATP concentration. They are usually open and leak potassium under conditions when cellular energy demand exceeds energy supply, for example during hypoxia or ischemia. They are also found in the central nervous system, smooth muscle and pancreas (Ashcroft, 1988). Their role in the control of insulin secretion has been well established (Petersen, 1990). Recent studies have shown that KATP channels are important in protecting the heart during ischemia (Grover et al. 1989; Gross and Auchampach, 1992) and during hypoxia (McKean and Branz, 1992). These channels have also been implicated in the phenomenon of preconditioning (Auchampach et al. 1992). The mechanism for cardiac protection has not been well established; however, KATP opening shortens the cardiac action potential and may limit calcium entry and reduce the metabolic demand of the myocyte (Cole et al. 1991). The channel opening is responsible for an initial extracellular accumulation of potassium that may also serve to decrease metabolic demand on the heart (Wilde et al. 1990). The open channels, however, could be detrimental to the heart during reperfusion or reoxygenation as they would facilitate re-entry phenomena and arrhythmias (Wolleben et al. 1989). Studies from this laboratory have shown that the heart of the semi-aquatic diving rodent, the muskrat (Ondatra zibethicus), is able to survive ischemia and hypoxia better than the heart of a similarly sized non-diving rodent, the guinea pig (McKean and Landon, 1982; McKean, 1984). We hypothesized that the KATP channel might be involved in the explanation for this species difference.
