Potentiation by endogenously released ATP of spontaneous transmitter secretion at developing neuromuscular synapses in Xenopus cell cultures

Abstract

1 Previously we have shown that extracellular application of ATP, a substance co-stored and coreleased with acetylcholine (ACh) in the peripheral nervous system, markedly potentiated the frequency of spontaneous synaptic currents (SSCs) produced by ACh. In the present study, we have further characterized the purinoceptor which mediates the potentiation effect of ATP and the role of endogenously released ATP.2 Pretreatment with a P2-purinoceptor antagonist, suramin (0.3 mM), but not a PI-purinoceptor antagonist, 8-phenyltheophylline (0.1 mM), prevented the potentiating effect of ATP. 3 We studied the role of endogenously released ATP by examining the effect of a specific P2-purinoceptor antagonist on the frequency of spontaneous synaptic events at high-activity synapses (> 3 Hz) and found that suramin, but not 8-phenyltheophylline markedly reduced the frequency of SSCs at these high-activity synapses. In addition, desensitizing the P2-purinoceptor with x,4-methylene ATP also produced similar effects to suramin. 4 Extracellular application of the L-type Ca2+ channel blockers, verapamil, nifedipine or diltiazem (10 pLM each) reduced SSC frequency of high-activity synapses, while the N-type Ca2+ channel blocker, omega-conotoxin had no appreciable effect. The potentiating effect of ATP was further prevented by pretreatment with the L-type Ca2+ channel blockers. On the other hand, Bay K 8644, which is a depolarization-dependent L-type Ca2+ channel agonist, potentiated SSC frequency at these high-activity synapses.5 These results suggest that endogenous release of ATP at developing neuromuscular synapses is responsible for the maintenance of high levels of spontaneous ACh release, which is known to play a crucial role in regulating postsynaptic differentiation.

Purinergic signalling during development and ageing

“…Since then, there have been a number of studies of the actions of ATP in developing Xenopus neuromuscular synapses (see [20]). Extracellular applications of ATP to developing Xenopus neuromuscular synapses in culture potentiate ACh responses of developing muscle cells during the early phase of synaptogenesis [21][22][23]. The possibility that extracellular ATP coreleased with ACh may serve as a positive trophic factor at developing neuromuscular synapses has also been raised [20,21].…”

Purinergic signaling in embryonic and stem cell development

“…Since then, there have been a number of studies of the actions of ATP in developing Xenopus neuromuscular synapses (see [11]). Extracellular applications of ATP to developing Xenopus neuromuscular synapses in culture potentiate ACh responses of developing muscle cells during the early phase of synaptogenesis [12][13][14]. The possibility that extracellular ATP coreleased with ACh, may serve as a positive trophic factor at developing neuromuscular synapses has also been raised [11,12].…”

Long‐term potentiation and long‐term depression induced by local application of ATP to hippocampal CA1 neurons of the Guinea pig

“…L-VOCCs have previously been reported to be distributed predominantly in the somatic and perisomatic regions of CA1 neurons (Christie et al, 1995), and the L-type Ca 2ϩ current also was enhanced by the external application of ATP or ATP␥S (Scamps et al, 1993;Fu and Huang., 1994). It is therefore very significant that nifedipine, an L-VOCC-type of blocker, suppressed almost completely the late-phase component (Fig.…”