single K⁺ channels of skeletal muscle from the rat and frog were into planar lipid bilayers and their properties were studied. Fusion was induced by an osmotic gradient. Of the four types of K⁺ channels recorded, the two most frequently observed were a voltage and Ca²⁺-activated K⁺ channel and a K⁺ channel with a prominent conductance substate. The first K⁺ channel was identified as the large Ca²⁺-activated K⁺ (BK) channel because the open-state probability was increased with depolarization (e-fold change per 10.6±3.5 mV, n=8) and internal Ca²⁺ (half-activation at 16.7±3.8 mV, n=8, pCa 4) and its conductance was large (247±4.9 pS, n=24 in 0.1 M KCI). Lifetime distributions of open- and closed-states could be fitted with single exponentials of several milliseconds. The mean open- and closed-lifetimes were linearly dependent on the intracellular [Ca²⁺] and 1/[Ca²⁺], respectively. The second K⁺ channel showed a conductance substate at 30 ~ 60% of the open state. Its current-voltage relation was linear in the range of -80 ~ +80 mV. The slope conductance of the substate and open-state were 40 and 144 pS in 0.2 M KCl, respectively. The channel was highly selective for K⁺ over Cl. The open-state probability was weakly voltage-dependent (e-fold change per 35 mV. The lifetime distributions of open- and closed-states were fitted with two exponentials and the major gating occurred slowly at several hundred milliseconds. Based on the above results, we think the second type of K⁺ channel is the sarcoplasmic reticulum K⁺ (SRK) channel. In addition, both types of channel were also incorporated into the lipids extracted from the skeletal muscle. The channel properties recorded in the bilayers termed from synthetic and extracted lipids were qualitatively similar. Our data indicate that BK and SRK channels are rich in the skeletal muscle and their properties and regulation could be effectively studied in planar lipid bilayer.