Ionomycin-induced acetylcholine release and its inhibition by adenosine at frog motor nerve endings

Increases in acetylcholine release produced by phorbol esters are not mediated by protein kinase C at motor nerve endings.

Recent work from our laboratory has demonstrated that phorbol esters known to stimulate protein kinase C (PKC) also stimulate acetylcholine (ACh) secretion by an action at a strategic component of the secretory apparatus [ J Physiol (Lond) 501:41-48]. In an attempt to determine whether the stimulatory effects of phorbols are mediated by PKC, we examined the effects of several PKC antagonists on...

Interaction of glutamate- and adenosine-induced decrease of acetylcholine quantal release at frog neuromuscular junction.

In a frog neuromuscular preparation of m. sartorius, glutamate had a reversible dose-dependent inhibitory effect on both spontaneous miniature endplate potentials (MEPP) and nerve stimulation-evoked endplate potentials (EPP). The effect of glutamate on MEPP and EPP is caused by the activation of metabotropic glutamate receptors, as it was eliminated by MCPG, an inhibitor of group I metabotropic...

Presynaptic inhibition of norepinephrine release from sympathetic nerve endings by endogenous adenosine.

ATP is coreleased with norepinephrine from sympathetic nerve endings and subsequently broken down to adenosine. In animal preparations, adenosine can inhibit norepinephrine release by stimulation of presynaptic receptors. We tested this feedback mechanism in humans by using a specific nucleoside transport inhibitor (draflazine) as a pharmacological tool to allow accumulation of endogenous adeno...

Extra- and intracellular sphingosylphosphorylcholine promote spontaneous transmitter release from frog motor nerve endings.

Similar to phosphatidylinositol bisphosphate, sphingomyelin breakdown generates several lipids, including sphingosylphosphorylcholine (SPC), that are putative signaling molecules. The present study was undertaken to evaluate the involvement of SPC in transmitter release process. Intracellular recordings were made from isolated frog sciatic-sartorius nerve-muscle preparations, and the effects of...

Spontaneous subthreshold activity at motor nerve endings.