Abstract
Effect of β-agkistrodotoxin (β-AgTx), a presynaptic neurotoxin purified from snake venom, on large-conductance calcium-activated potassium channels (BK Ca) was studied in rat hippocampal CA1 pyramidal neurons using inside-out configuration of patch-clamp technique. The results showed that in equimolar K + (150 mM) and 1 μM intracellular Ca 2+ conditions, internal application of β-AgTx inhibited the activity of BK Ca by reducing open probability ( P o) of the channels in a concentration-dependent manner. High concentration (74 nM) of β-AgTx completely eliminated opening of the channels. However, 37 nM β-AgTx (at −40 mV) decreased P o from 0.49±0.07 to 0.03±0.03, switched two open time constants (0.51±0.32 and 8.77±1.63 ms) to be a single time constant of 0.46±0.40 ms. The results indicate that inhibition of BK Ca by β-AgTx may account for the facilitatory phase of the toxin on acetylcholine release from nerve terminals.
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