Substance P produces an inward current by suppressing voltage-dependent and -independent K+ currents in bullfrog primary afferent neurons.
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 microM) 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 much greater than NKB. An antagonist for SP receptors, [D-Arg1, D-Trp7,9, Leu11]SP, did not prevent the response to SP. SP (3 nM to 1 microM) suppressed the voltage-dependent non-inactivating K+ current, the M-current (IM) by reducing the maximum M-conductance. A voltage-independent background K+ current, IK(B), could be recorded at a hyperpolarizing voltage (< or = -60 mV) from DRG neurons. SP (3 nM to 1 microM) produced the inward current associated with decreased IK(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 IM and IK(B) that are regulated by intracellular activity of ATP in bullfrog DRG neurons.
Ishimatsu
M
M
Department of Physiology, Kurume University School of Medicine, Japan.
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002586:Cesium / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000166:cytology / Q000502:physiology; D007425:Intracellular Membranes; D009475:Neurons, Afferent / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D011892:Rana catesbeiana; D013373:Substance P / Q000494:pharmacology*; D015320:Tachykinins / Q000494:pharmacology
D015320:Tachykinins; D002586:Cesium; D013373:Substance P; D000255:Adenosine Triphosphate; D011188:Potassium