Substance P activates a non-selective cation channel in murine pacemaker ICC.

Interstitial cells of Cajal (ICC) associated with Auerbach's plexus in the small intestine, provide pacemaker activity to orchestrate peristalsis and mixing. Despite the close apposition between ICC and enteric nerves, little is known about the neural regulation of pacemaker activity. The present study pursues the hypothesis that substance P can affect pacemaker activity through action on non-selective cation channels. Cell-attached and inside-out patch clamp studies were performed on isolated ICC in short-term cultures that provided evidence that substance P increases open probability or initiates activity in non-selective cation channels in ICC. The single-channel conductance is approximately 25 pS and in the on-cell configuration the activity can occur in a rhythmic fashion. Patches contained 1-10 channels and were most often accompanied by a approximately 12 pS chloride channel that was also activated by substance P. In a recently developed preparation that allows patch clamping in ICC in their natural environment within tissue, i.e. in situ, the presence of the channel and substance P activation was confirmed. The non-selective cation channel is one of the channels that initiate intestinal pacemaker activity and the present study provides further single-channel data on this critical channel. Because of the close proximity of enteric motor and sensory nerves to ICC, these data provide a potential mechanism underlying neural regulation of pacemaker activity. The data also indicate that neurokinergic pharmacology is a promising avenue for excitation of the intestinal pacemaker system.