Abstract
A whole-cell patch-clamp study was carried out to examine the effect of substance P (SP) on the excitability of neurons in bullfrog dorsal root ganglia (DRG). SP (3 nM to 1 μM) produced an inward current associated with decreased membrane conductance at voltage range between −10 and −130 mV. Neurokinin A (NKA) and neurokinin B (NKB) also produced the inward current in DRG cells; the rank order of agonist potency was NKA = SP ⪢ NKB. An antagonist for SP receptors, [D-Arg 1, D-Trp 7,9, Leu 11]SP, did not prevent the response to SP. SP (3 nM to 1 μM) suppressed the voltage-dependent non-inactivating K + current, the M-current ( I M) by reducing the maximum M-conductance. A voltage-independent background K + current, I K(B), could be recorded at a hyperpolarizing voltage (≤−60 mV) from DRG neurons. SP (3 nM to 1 μM) produced the inward current associated with decreased I K(B) at a holding potential more negative than −60 mV. The SP-induced inward current reversed its polarity at the equilibrium potential for K ions. Intracellular dialysis with Cs + blocked the SP-induced responses. Depletion of intracellular ATP reduced SP-induced inward current. These results suggest that the SP-induced inward current was due to suppression of both the I M and I K(B) that are regulated by intracellular activity of ATP in bullfrog DRG neurons.
Published Version
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