Two independent pathways mediated by cAMP and protein kinase A enhance spontaneous transmitter release at Drosophila neuromuscular junctions

J Neurosci. 2000 Nov 15;20(22):8315-22. doi: 10.1523/JNEUROSCI.20-22-08315.2000.

Abstract

cAMP is thought to be involved in learning process and known to enhance transmitter release in various systems. Previously we reported that cAMP enhances spontaneous transmitter release in the absence of extracellular Ca(2+) and that the synaptic vesicle protein neuronal-synaptobrevin (n-syb), is required in this enhancement (n-syb-dependent; Yoshihara et al., 1999). In the present study, we examined the cAMP-induced enhancement of transmitter release in the presence of external Ca(2+). We raised the intracellular concentration of cAMP by application of either forskolin, an activator of adenylyl cyclase, or by 4-chlorophenylthio-(CPT)-cAMP, a membrane-permeable analog of cAMP, in the presence of external Ca(2+), while recording miniature synaptic currents (mSCs) at the neuromuscular junction in n-syb null mutant embryos. The frequency of mSCs increased in response to elevation of cAMP, and this effect of cAMP was completely blocked by Co(2+) (n-syb-independent pathway). In contrast, in wild-type embryos the cAMP-induced mSC frequency increase was partially blocked by Co(2+). In a mutant, DC0, defective in protein kinase A (PKA), nerve-evoked synaptic currents were indistinguishable from the control, but mSCs were less frequent. In this mutant the enhancement by cAMP of both nerve-evoked and spontaneous transmitter release was completely absent, even in the presence of external Ca(2+). Taken together, these results suggest that cAMP enhances spontaneous transmitter release by increasing Ca(2+) influx (n-syb-independent) as well as by modulating the release mechanism without Ca(2+) influx (n-syb-dependent) in wild-type embryos, and these two effects are mediated by PKA encoded by the DC0 gene.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenylyl Cyclases / metabolism
  • Animals
  • Calcium / metabolism
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / metabolism
  • Cobalt / pharmacology
  • Colforsin / pharmacology
  • Cyclic AMP / analogs & derivatives
  • Cyclic AMP / metabolism*
  • Cyclic AMP / pharmacology
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Drosophila
  • Drosophila Proteins*
  • Electric Stimulation
  • Evoked Potentials / drug effects
  • In Vitro Techniques
  • Insect Proteins / genetics
  • Muscle Contraction / drug effects
  • Muscle Contraction / genetics
  • Muscle Contraction / physiology
  • Mutation
  • Myosin Heavy Chains / genetics
  • Neuromuscular Junction / metabolism*
  • Neuropeptides / deficiency
  • Neuropeptides / genetics
  • Neurotransmitter Agents / metabolism*
  • Organ Specificity / genetics
  • Patch-Clamp Techniques
  • R-SNARE Proteins
  • Reaction Time / drug effects
  • Reaction Time / genetics
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology*
  • Tetrodotoxin / pharmacology
  • Vesicular Transport Proteins*

Substances

  • Calcium Channel Blockers
  • Calcium Channels
  • Drosophila Proteins
  • Insect Proteins
  • Neuropeptides
  • Neurotransmitter Agents
  • R-SNARE Proteins
  • Vesicular Transport Proteins
  • nsyb protein, Drosophila
  • Colforsin
  • Cobalt
  • Tetrodotoxin
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • Myosin Heavy Chains
  • Adenylyl Cyclases
  • Calcium