ATP- and acetylcholine-activated channels co-existing in cell-free membrane patches from rat sympathetic neuron.

The interaction between ATP-activated channels and the nicotinic receptor-channels has been reported in neuronal cells. To elucidate the mechanisms underlying the interaction, the currents activated by ATP and acetylcholine (ACh) were recorded from cell-free membrane patches excised from rat sympathetic neurons. When ATP or ACh (30-300 microM) was applied, the current consisting of multiple channels was observed in most outside-out patches. The amplitude of the ATP-activated current and that of the ACh-activated current in the same patches were highly correlated (r = 0.89). In a part of the patches, the current activated by ACh (300 microM) with ATP (300 microM) was smaller than the current successively activated by ACh alone, indicating that ATP did not add the current but rather inhibited the ACh-activated channels. In addition, the decay of the current activated by ACh with ATP was faster than the current activated by ACh alone. The coexistence of the two types of channels in the same patches and the interaction of ATP with the ACh-activated current in the cell-free condition may support our previous hypothesis, namely, the activation by ATP of a subpopulation of the nicotinic receptor-channels.