Modulation by oxytocin of ATP-activated currents in rat dorsal root ganglion neurons

The modulatory effect of oxytocin (OT) on ATP-activated currents (I(ATP)) was studied in freshly isolated dorsal root ganglion (DRG) neurons of rats using whole cell clamp technique. In most of the neurons examined (50/70, 71.4%) extracellular application of OT (10(-9)-10(-5) mol/L) suppressed I(ATP) while in the rest (20/70, 28.6%) no modulatory effect was observed. OT shifted the ATP concentration-response curve downwards with a decrease of 39.8+/-4.2% in the maximal current response and with no significant change of Kd value. This OT-induced inhibition of I(ATP) showed no voltage dependence, and could be blocked by [d(CH(2))(5),Tyr(Me)(2),Thr(4),Tyr-NH(2)(9)]-OVT (d(CH(2))(5)-OVT) (10(-8) mol/L), a specific OT receptor antagonist. Intracellular application of H-9 (4 x 10(-5) mol/L, an inhibitor of protein kinase A) (n=12), BAPTA (10(-2) mol/L, a chelator of calcium ions) (n=4) could reverse the inhibitory effect of extracellular OT (10(-7) mol), while inclusion of H-7 (2 x 10(-5) mol/L, a protein kinase C inhibitior) (n=8) and KN-93 (10(-5) mol/L, an inhibitor of CaMKII) (n=9) in the recording pipette did not affect this effect. The results suggested that OT inhibition on ATP-activated currents was mediated by OT receptors in the membrane of DRG neurons; and this inhibitory effect involved the transduction of intracellular cAMP-PKA and Ca(2+).