The effect of the neuropeptide substance P on desensitization of ATP receptors of PC12 cells

1 Patch clamp recording (whole cell configuration) was employed to investigate the modulatory action of substance P on inward currents elicited by adenosine 5'-triphosphate (ATP, focally applied via a pressure pipette) from phaechromocytoma (PC12) cells usually held at -70 mV. 2 Bath-applied substance P (0.2-20 mu M) had no effect on baseline membrane current but reversibly reduced ATP peak currents in a concentration-dependent fashion. The depressant effect was not associated with a change in the ATP current reversal potential. 3 Equiamplitude peak responses induced by 50 mu M or 5 mM ATP were differentially affected by substance P which preferentially reduced currents evoked by 5 mM ATP. In the presence of substance P a conditioning pulse of ATP evoked a stronger depression to subsequent test pulses of the same agonist. 4 Combined patch clamping and confocal laser imaging of intracellular Ca2+ ([Ca2+](i)) of single PC12 cells showed that substance P (applied by a pressure pipette) pet se had no effect on [Ca2+](i) or current baseline, although it reduced the inward current and associated [Ca2+](i) rise elicited by ATP. 5 These results are interpreted as due to facilitation by substance P of desensitization of ATP-gated P-2X2 receptors of PC12 cells. It is proposed that the novel modulation by this peptide of ATP responses may serve as a model for further studies aimed at elucidating the action of substance P on purinergic neurotransmission.