Synchronous release of ATP and neurotransmitter within milliseconds of a motor nerve impulse in the frog

1. It has been suggested that ATP is released together with the neurotransmitter acetylcholine (ACh) and, after hydrolysis to adenosine, is the primary physiological mediator of prejunctional neuromuscular depression. To evaluate whether ATP is released with sufficient rapidity to mediate prejunctional depression, outside-out patches containing both ATP-gated and ACh-gated ion channels were made from acutely dissociated guinea-pig sympathetic neurons and used to detect the co-release of nucleotide and neurotransmitter in frog cutaneous pectoris nerve-muscle preparations. 2. In a normal bathing solution in which muscle nicotinic receptors were blocked, a single stimulus to the motor nerve produced channel openings in the detector patch characteristic of both ATP and ACh. 3. In the remaining experiments, preparations were treated with sufficient hexamethonium (200 mu M) to block nicotinic responses in the detector patch. In these experiments, a single temporally isolated nerve impulse caused the synchronous opening of ATP-gated channels in the detector patch with a latency of <5 ms when patches were placed within 10 mu m of the motor nerve ending. This multichannel phasic response was followed by a trail of discrete channel openings characteristic of ATP-gated channels. 4. The selective ATP antagonist suramin (50 mu m) reversibly eliminated the response to nerve stimulation. 5. The results suggest that ATP is released synchronously together with the neurotransmitter ACh in response to an individual nerve impulse and with a brief latency characteristic of quantal release from synaptic vesicles.