Two types of potassium channels from the internal membrane system of the crayfish muscle incorporated into planar lipid bilayers.

Potassium channels constitute the most diverse and widespread class of ion channels known. K channels have been found in all cells which display action potentials mediated by sodium or calcium ions. The different types of K channels are very often present in the same cells which shows, that their diversity is not associated with the cell type (for review see Latorre and Miller 1983; Rudy 1988). A recent advance has been the incorporation of ion channels into planar lipid bilayers, which enables the study of channels not accessible to patch-clamp pipette. In skeletal muscle, Ca -activated K channels (Latorre et al. 1982; Moczydlowski and Latorre 1983; Eisenman et al. 1986; Oberhauser et al. 1988) and K selective SR channels (Miller 1978; Labarca and Miller 1981) have been described using this technique. These channels were favorite objects to study in planar lipid bilayers, because of their high conductance (150—250 pS, depend­ ing on concentration of K ions). In the case of Ca-activated K channel its kinetic behavior (McManus and Magleby 1988) and pharmacology (Strong 1990; Oberhauser et al. 1988) are well described. We report here the results of a study into the composition of channels of the internal membrane system of crayfish muscle fibres, which are known to spike on the calcium principle (for review see Zachar 1971). They thus differ qualitatively from the muscle fibres, which generate sodium action potentials, both on the surface and in the tubular membranes. Three kinds ofK 4 channels have been described in these fibres in voltage clamp conditions (Henček et al. 1978; Mounier and Vassort 1975). The results presented concern two types of K f channels in the internal