| This experiment aimed to investigate the modulation of hypotonicity on ATP-activated currents (IATP) in primary sensory neurons. Whole cell-patch clamp recording was performed on cultured SD rat trigeminal ganglion (TG) neurons. (1) The majority of neurons examined (80.90%) were sensitive to ATP (10-5~10-3M), ATP activated an inward currents in a concentration-dependent manner, and IATP were blocked by PPADS(pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid, an antagonist of the P2X receptor. (2)When Hypotonicity(220 mOsm, 260 mOsm, 300 mOsm)was preapplied extracellularly, it reduced ATP-activated currents (IATP) significantly. This inhibitory effect was reversible, osmosis-dependent, and voltage-independent. (3) The concentration-response curves for ATP with and without preapplication of hypotonicity showed that preapplication of hypotonicity shifted the curve downward; maximal amplitude of IATP with hypotonicity decreased by 25.26±2.41%, while the threshold value remained unchanged; the EC50 value of the two curves were very close(1.19×10-4M vs 1.33×10-4M). (4) This inhibitory effect was increased by 4ɑ-PDD, a selective TRPV4 receptor agonist, and was reversed by ruthenium red (RR), a nonselective TRPV4 receptor antagonist, suggesting that the inhibition is mediated via TRPV4 receptor. (5) Preapplication of forskolin or 8-Br-cAMP partly reversed the inhibition of IATP by hypotonicity, whereas preapplication of H89 had not effect on it. These results suggested that hypotonicity inhibited ATP-actived currents via TRPV4 receptor, which was mediated partly by reducing cAMP concentration directly rather than by PKA and downstream process.
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