Introduction A new class of K + channels that link membrane potential to the bioenergetic situation of the cell has been recently discovered (Noma 1983). These K + channels (KATP) are normally closed at physiological intracellular ATP concentrations and open upon a diminution of [ATP]in. These channels have been shown to be present in pancreatic B-cells (Ashcroft et al. 1984; Cook and Hales 1984; Rorsman and Trube 1985a; Rorsman and Trube 1985b), cardiac ventricular cells (Noma 1983; Trube and Hescheler 1984) and skeletal muscle (Spruce et al. 1985; Spruce et al. 1986; Spruce et al. 1987). They might also be present in the central nervous system (Ashford et al. 1988; Bernardi et al. 1988) and in smooth muscle (Quast 1988; Quast and Cook 1988).