Modulation of Presynaptic Transmitter Release by ATP Derived from Postsynaptic Sources
Both ATP and adenosine have long been known to be neurotransmitters released from presynaptio cells. However, ATP may also be released from stimulated postsynaptic cells. This has been observed in frog (1) and human (2) muscle as well as Torpedo electric organ (3). Moreover, exogenous ATP has been shown to reduce transmitter release from presynaptic terminals of preganglionic sympathetic neurons (4) and motoneurons (5). Likewise adenosine also depresses synaptic transmission in the central nervous system (6,7). One prime explanation for this phenomenon might be that Ca2+ entry into the terminals is somehow altered. However, this seems unlikely, because the depressant effect is independent of extracellular Ca2+ concentrations (7). Thus, some other mechanism must be involved, and it remains unknown.
KeywordsSucrose Depression Adenosine Acetylcholine Adenine
Unable to display preview. Download preview PDF.
- 1.Bood LG, Koketsu K, Miyamoto S: Outflux of various phosphates during membrane depolarization of excitable tissues. Am. J. Physiol. 202:469–474, 1962.Google Scholar
- 2.Orrester T: An estimate of adenosine triphosphate release into the venous effluent from exercising human forearm muscle. J. Physiol. (Lond.) 224:611–628, 1972.Google Scholar
- 5.Ribeiro JA, Walker J: The effects of adenosine triphosphate and adenosine diphosphate on transmission at the rat and frog neuromuscular junctions. Br. J. Pharmac. 54:213–218, 1975.Google Scholar
- 7.Dunwiddie TV: Interactions between the effects of adenosine and calcium on synaptic responses in rat hippocampus in vitro. J. Physiol. (Lond.) 350:515–559, 1984.Google Scholar
- 10.Niles WD, Smith DO: Effects of hypertonic solutions on quantal transmitter release at the crayfish neuromuscular junction. J. Physiol. (Lond.) 329:185–202, 1980.Google Scholar
- 11.Lowry O, Passonneau JV: A Flexible System of Enzymatic Analysis. Academic Press, New York, 1972, Pp.223–235.Google Scholar