ATP-GATED CATION CHANNELS (P2X PURINOCEPTORS) IN TRIGEMINAL MESENCEPHALIC NUCLEUS NEURONS OF THE RAT

1. We have investigated whether receptors for ATP exist on neurones of the trigeminal mesencephalic nucleus (MNV) of the rat using whole-cel l and outside-out patch-clamp recording in coronal brainstem slices. 2 . With whole-cell recording, the bath application of ATP, adenosine 5' -0-[3-thiotriphosphate] (ATP gamma S) and alpha,beta methylene adenosi ne triphosphate (alpha beta meATP) caused concentration-dependent inwa rd currents in all cells tested (holding potential, -62 mV), With EC(5 0) values of 437, 15 and 254 mu M, respectively. All three agonist-evo ked currents developed rapidly (rise time, similar to 10-25 s), desens itized slowly (over similar to 20-50 s), cross-desensitized with each other, were associated with an increase in membrane conductance and we re attenuated by the application of suramin (30 mu M). 3. The inward c urrent evoked by ATP decreased as the membrane potential was made less negative and had a zero current potential of +1.0 +/- 3.7 mV. The cur rent-voltage relationship showed marked inward rectification. 4. Brief flickery single-channel openings could be resolved in response to ATP (3 mu M) in outside-out membrane patches. Unitary current at -82 mV w as -1.81 +/- 0.2 pA, which corresponds to a unitary conductance of 22 pS. 5. We conclude that proprioceptive MNV neurones contain ATP-gated cation channels. Such P2X purinoceptors may be involved in the process ing of proprioceptive information, thus suggesting a potentially impor tant physiological role of ATP.