Inhibiting BK channels at the crayfish neuromuscular junction decreases amplitudes of single pulse EPSPs and increases synaptic facilitation

Abstract

Since BK channels serve to regulate neurotransmitter release at synapses in the rat hippocampus (Raffaelli et al., 2004), inhibition of the channels could have significant effects on synaptic activity at the crayfish neuromuscular junction. We studied the effects of charybdotoxin, a BK channel inhibitor, on the resting membrane potential, action potential threshold, excitatory post-synaptic potentials (EPSPs), and synaptic facilitation in the crayfish neuromuscular junction (NMJ). We measured the effects of the neurotoxin by observing the crayfish tail dissection in standard crayfish Ringers solution (control), Ringers solution with charybdotoxin (toxin), and again in standard Ringers solution (wash) using suction and recording electrodes in conjunction with an electrical stimulator and a data collection program. With the addition of charybdotoxin, we observed an increase in the resting membrane potential, a slight decrease of the action potential threshold, a significant decrease in the amplitude of the EPSPs, and an observed increase in the facilitation of EPSPs with a 20ms delay between pulses. Our results reveal that BK channels regulate neurotransmitter release in a manner distinct from other presynaptic voltage- and calcium-activated potassium channels in that they may function in the dampening of facilitation. In addition, the decrease in the amplitude of single pulse EPSPs indicates that BK channels may affect postsynaptic potentiation.