The role of calcium-activated potassium channels in excitatory postsynaptic potential duration

Abstract

Our research looks at the role of calcium-activated potassium channels (K_Ca channels) in synaptic transmission. K_Ca channels play a potentially significant role in repolarization duration of the presynaptic cell following an action potential. Additionally, focusing on the function of these channels may offer insights into the significance of extracellular calcium concentrations on the process of transmission. We expected that the time taken for repolarization of the presynaptic cell would correspond to the duration of excitatory postsynaptic potentials which we could then record. We used 3,4-diaminopyridine (3,4-DAP) to block delayed-rectifier potassium channels in the crayfish NMJ, so that we could study calcium-activated ones exclusively, and then modulated extracellular calcium concentrations to see its effect on EPSP duration. We hypothesized that by blocking delayed-rectifier potassium channels, we would inhibit repolarization of the presynaptic cell, resulting in a broadened EPSP in the postsynaptic cell. Our second hypothesis was that lowering extracellular calcium concentrations for 3,4-DAP-exposed crayfish cells would further inhibit repolarization as Ca²⁺ ions are required to activate KCa channels. Our results demonstrated a statistically significant difference in repolarization time between 3,4-DAP-exposed crayfish and unexposed crayfish, but this difference contradicted our hypothesis. Instead of lengthening repolarization duration, 3,4-DAP shortened it. We also found extracellular calcium concentrations to have an effect on EPSP duration: the lower the extracellular calcium concentration, the broader the EPSP measured. This result was in keeping with our second hypothesis. One explanation we offer for these results is that K_Ca channels might become more efficient in the presence of 3,4-DAP and/or the blockage of other potassium channels, and that extracellular calcium concentrations might in turn regulate this efficiency.