Substance P induces inward current and regulates pacemaker currents through tachykinin NK1 receptor in cultured interstitial cells of Cajal of murine small intestine

We investigated whether substance P modulates pacemaker currents generated in cultured interstitial cells of Cajal of murine small intestine using whole cell patch-clamp techniques at 30 degreesC. Interstitial cells of Cajal generated spontaneous inward currents (pacemaker currents) at a holding potential of -70 mV Tetrodotoxin, nifedipine, tetraethylammonium, 4-aminopyridine, or glibenclamide did not change the frequency and amplitude of pacemaker currents. However, divalent cations (Ni2+, Mn2+, Cd2+, and Co2+), nonselective cationic channel blockers (gadolinium and flufenamic acid), and a reduction of external Na+ from normal to 1 mM inhibited pacemaker currents indicating that nonselective cation channels are involved in their generation. Substance P depolarized the membrane potential in current 7,9 clamp mode and produced tonic inward pacemaker currents with reduced frequency and amplitude in voltage clamp mode. [D-Arg(1), D-Trp(7,9) Leu(11)] substance P, a tachykinin NK1 receptor antagonist, blocked these substance P-induced responses. Furthermore, [Sar(9), Met(O-2)(11)] substance P, a specific tachykinin NK1 receptor agonist, depolarized the membrane and tonic inward currents mimicked those of substance P. Substance P continued to produce tonic inward currents in external Ca2+-free solution or in the presence of chelerythrine, a protein kinase C inhibitor. However, substance P-induced tonic inward currents were blocked by thapsigargin, a Ca2+-ATPase inhibitor in the endoplasmic reticulum or by an external 1 mM Na+ solution. Our results demonstrate that substance P may modulate intestinal motility by acting on the interstitial cells of Cajal by activating nonselective cation channels via the release of intracellular Ca2+ induced by tachykinin NK1 receptor stimulation. (C) 2004 Elsevier B.V. All rights reserved.