[The implication of stimulus-evoked ATP release from neuronal and extraneuronal sites]

Characteristics of the ATP release from non-neuronal tissues were reviewed in connection with that from neuronal tissues. alpha 1-Adrenoceptor and M3-cholinoceptor stimulation produced a postjunctional ATP release from smooth muscles such as the vas deferens and ileal longitudinal muscles of the guinea pig, suggesting the existence of a coupling mechanism between the stimulation of the receptor for the transmitter and postjunctional ATP release. Accompanied with positive inotropic action, cardiotonics elicit postjunctional ATP release, which is derived from mitochondria, in atrial muscles, whereas these drugs are incapable of producing the release from papillary muscles. Possible physiological roles of ATP released to synapses from nonneuronal tissues are considered as follows: 1) the nucleotide may act as an opener of Ca2+ and K+ channels, 2) ATP in the synapse seems to serve as a transsynaptic neuromodulator after conversion to adenosine.