A307 EFFECT OF SLOW SYNAPTIC EXCITATION ON MYENTERIC INTRINSIC PRIMARY AFFERENT NEURON BKCA CHANNEL ACTIVITY

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 contractions1. 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. To determine if slow synaptic excitatory input alters BKCa channel activity. All experiments were performed on longitudinal-muscle myenteric preparations prepared from jejunal segment taken from freshly euthanized adult male Swiss Webster mice. Segments were placed into a 95% carbogen bubbled Krebs solution containing 2 µM nicardipine and 1 µM scopolamine, and the myenteric plexus exposed by microdissection. BKCa channel activity was recorded in situ patch clamping in cell-attached mode. BKCa channel activity was recorded at trans-patch potentials that were varied by 20 mV steps to determine voltage-sensitivity. Such recordings were performed before during and after presynaptic electrical stimulation designed to evoke postsynaptic sEPSPs. After recording the morphotype was verified by intracellular injection of a marker dye (neurobiotin). Analysis of unitary channel recordings revealed increased BKCa open probability (NPo) at fixed trans-patch potentials following sEPSPs. An increased NPo which lasted 30 s to 1 min was also observed. All BKCachannels were independently voltage sensitive with increased NPo during patch depolarisation. 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. NSERC