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Properties of large-conductance Ca~(2+) -achvated K~+ (BK_(Ca)channel were studied in ex-cised patches of pyramidal neurons from adult rat hippocampal CAl region using inside-out single channel recording technique. Activity of BK_(Ca)channel was first oborved at[Ca] = l0~(-8)M with the membrane potential of + 20 mV, and the [Ca]_i at which the channel was half activated(P_0 = 0.5)was 2 x 10~(-6)M. Conductance of single BK_(Ca) channel was approx.245 pS with symmetrical 140 mM-K~+ on bo sides of the excisedmembrane,essentially independent of membrane potentials and [Ca]_i, tested. Two exponentials, with the time constants of 2.07 ma and 14.36ms at membrane potential of + 40 mV with 5×10~(-7) M-[Ca]_i,were requied to describe the observed open distrbution of BK_(Ca) channel, sug-gesting existence of two different open channel stathes with apparently normal conductance. BK_(Ca)channel occasionally entered an apparent thirdopen channel state with a single channel current amplitude about 45% the amplitude o
Properties of large-conductance Ca ~ (2+) -achvated K ~ + (BK_ (Ca) channels were studied in ex-cised patches of pyramidal neurons from adult rat hippocampal CAl region using inside-out single channel recording technique. Activity of BK_ (Ca) channel was first oborved at [Ca] = 10 ~ (-8) M with the membrane potential of + 20 mV, and [Ca] _i at which the channel was half activated (P_0 = 0.5) was 2 x 10 ~ (-6) M. Conductance of single BK_ (Ca) channel was approx. 245 pS with symmetrical 140 mM-K ~ + on bo sides of the excised membrane, essentially independent of membrane potentials and [Ca] _i, tested. Two exponentials , with the time constants of 2.07 ma and 14.36 ms at membrane potential of + 40 mV with 5 × 10 -7 M- [Ca] _i, were requied to describe the observed open distrbution of BK_ (Ca) channel, sug -gesting existence of two different open channel stathes with apparently normal conductance. BK_ (Ca) channel occasionally entered apparent third channel state with a single channel current amplitude about 4 5% the amplitude o