Substance P-mediated membrane currents in voltage-clamped guinea pig inferior mesenteric ganglion cells

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Abstract
Responses to substance P (SP) and to hypogastric nerve stimulation were recorded from voltage‐clamped guinea pig inferior mesenteric ganglion (IMG) neurons, and compared with those to muscarine. Muscarine produced a voltage‐dependent inward current accompanied by a reduced input conductance and inhibition of IM a time‐ and voltage‐dependent K+‐current (Brown and Adams: Nature 283:673–676, 1980). SP also produced an inward current, accompanied by a fall in input conductance (20 out of 31 cells) or a rise in input conductance (7 out of 31 cells). The fall in input conductance was not accompanied by an inhibition of M‐current (unlike frog ganglia: Adams et al.: British Journal of Pharmacology 79:330–333, 1983) or an inhibition of the inward rectifier current (unlike globus pallidus neurons: Stanfield et al.: Nature 315:498–501, 1985). Repetitive hypogastric nerve stimulation (10–20 Hz, 2–10 s) produced a slow inward postsynaptic current lasting 1–3 min, with decreases or increases of input conductance matching those produced by SP. The postsynaptic current did not show a consistent or reproducible change in amplitude on varying the holding potential between ‐90 and ‐25 mV. It is concluded that SP and hypogastric stimulation produce complex and variable changes in ionic conductance in IMG neurons.