CHARACTERIZING LARGE CONDUCTANCE POTASSIUM CHANNELS IN THE INTRINSIC PRIMARY AFFERENT NEURONS OF MOUSE JEJUNUM

Abstract

The large conductance calcium dependent potassium (BKCa) channels are expressed in a large variety of cell types including neurons where they modulate excitability and action potential shape. Within the enteric nervous system, stretch-sensitive BKCa channels are expressed on intrinsic primary afferent neurons (IPANs) where they decrease the neurons’ excitability during intestinal contractions. A major determinant of peristalsis is slow excitatory neurotransmission (sEPSPs) within the IPAN to IPAN sensory network, and we wondered whether such transmission might also alter BKCa channel opening. All experiments were performed on longitudinal-muscle myenteric preparations prepared from jejunal segment taken from freshly euthanized adult male Swiss Webster mice. With the myenteric plexus exposed by microdissection, BKCa channel activity was recorded in cell-attached mode via the patch clamp technique. BKCa channel activity was recorded before and after presynaptic electrical stimulation, which was designed to evoke postsynaptic sEPSPs. The morphotype was verified by intracellular injection of a marker dye (neurobiotin). In addition, a blocker and opener were used to identify the effects of BKCa currents on IPAN properties. Analysis of unitary channel recordings revealed increased BKCa open probability (NPo) at fixed trans-patch potentials following sEPSPs. All BKCa channels were independently voltage sensitive with increased NPo during patch depolarisation. Analysis of whole-cell experiments also revealed BKCa channels have a significant effect on the undershoot amplitude of action potentials, and the rate at which IPANs repolarise. This study demonstrates that sEPSPs within the enteric nervous system modulate the function of BKCa channels in IPANs adding to the mechanistic understanding of enteric synaptic transmission and providing a potential target for therapeutic modulation of enteric nervous system excitability.