1. Archive
2. Vol.51, No.6

Properties of Large Conductance Calcium-Activated Potassium Channels in Pyramidal Neurons from the Hippocampal CA1 Region of Adult Rats

Abstract: The properties of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels were studied in rat hippocampal CA1 pyramidal neurons by using the patch-clamp technique in the excised-inside-out-patch configuration. The lowest [Ca²⁺]_i in which BK_Ca channel activities were observed was 0.01 M with the membrane potential of +20 mV and the [Ca²⁺]_i at which P_O of the channel is equal to 0.5 was 2 M. The unitary conductance of the single BK_Ca channel was 245.4 pS with symmetrical 140 mM K⁺ on both sides of the excised membrane. With a fixed [Ca²⁺]_i of 2 M, P_O increased e-fold with a 17.0 mV positive change in the membrane potential. Two exponentials, with time constants of 2.8 ms and 19.2 ms at the membrane potential of +120 mV with 2 M [Ca²⁺]_i, were required to describe the observed open time distribution of BK_Ca channel, suggesting the existence of two distinct open channel states with apparently normal conductance. A BK_Ca channel occasionally entered an apparent third open channel state with the single channel current amplitude about 45% of the normal amplitude. The properties of BK_Ca channel, which were found in this study to be more steeply dependent on voltage and more sensitive to [Ca²⁺]_i in adult hippocampal neurons than in cultured or immature hippocampal neurons, may be responsible for the shortened duration of action potential in hippocampal CA1 pyramidal neurons of adult rat.

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