[Effect of substance P on the somatic membrane of rat DRG neurons]

Intracellular recordings were performed on isolated rat DRG neurons to investigate the changes in the membrane potential in response to substance P and the involved ionic mechanisms. The resting membrane potential examined was -58.9 +/- 8.2 mV (X +/- SE) (n = 81). The conduction velocities estimated were: 20.4 +/- 4.8 m/s (X +/- SE) ranging from 14.1 to 28.7 m/s (47/60) in type A(alpha beta) cell, 9.8 +/- 5.2 m/s (X +/- SE) ranging from 1.2 to 13.7 m/s (13/60 in type A(delta) and type C cell. In majority of the neurons bath application of SP (10(-7) - 3 x 10(-4) mol/L) induced marked membrane potential depolarization (56/60). The membrane conductance increased 24.6% in average from control value of 2.72 x 10(-8) S during SP-induced depolarization (n = 3). The reversal potential was between +40 - %50 mV (n = 3). When NaCl in BSS was substituted with choline chloride or containing TTX (10(-5) mol/L), the amplitude of SP-induced depolarization attenuated markedly but not incompletion eventually. When high (20 mmol/L) and low (0 mmol/L) Ca2+ BSS was used, the amplitude of SP-induced depolarization increased and decreased respectively. However, when BSS containing 10(-4) mol/L Cd2+ or 10(-2) mol/L TEA was used SP-induced depolarization was reduced. The above results indicate that SP-induced depolarization involves a rather multiple changes in ionic conductance.