Ammonium ions abolish excitatory synaptic transmission between cerebellar neurons in primary dissociated tissue culture.
1. Transmitter glutamate is thought to be derived from glutamine via cleavage by glutaminase. NH+4 inhibits glutaminase. Therefore the decrease of glutamatergic excitatory synaptic transmission by NH+4 was thought to be due to the inability of glutamine to serve as precursor for glutamate. However, in cat spinal cord, NH+4 abolished excitatory synaptic transmission by a conduction block for action potentials in presynaptic terminals. The conduction block prevented inferences as to the effects of NH+4 on the availability of glutamate for synaptic transmission. This study reexamines the effects of NH+4 on glutamatergic excitatory synaptic transmission in cerebellar neurons in tissue culture. 2. Whole-cell patch voltage-clamp recordings were obtained from presumed Purkinje cells. Extracellular stimulation of presumed granule cells produced mono- and polysynaptic excitatory postsynaptic currents (EPSCs). In addition, presumed Purkinje cells showed spontaneous EPSCs that occurred independently of the addition of tetrodotoxin (TTX) or Cd2+ to the extracellular solution. 3. NH+4 (5-10 mM) abolished evoked mono- and polysynaptic EPSCs without abolishing spontaneous EPSCs and without significant effects on action currents in the Purkinje cell soma. 4. Increase of K+ in the extracellular solution to 10-12 from 5 mM abolished evoked EPSCs without abolishing spontaneous EPSCs and without significant effects on action currents in the Purkinje cell soma. 5. Mixtures of NH+4 and K+, with each ion in a concentration insufficient to affect evoked EPSCs when given alone, abolished evoked EPSCs when the sum of NH+4 and K+ exceeded 10-12 mM. 6. Increase of intracellular pH by trimethylamine had no effect on evoked and spontaneous EPSCs.(ABSTRACT TRUNCATED AT 250 WORDS)
Raabe
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Department of Neurology, Veterans Affairs Medical Center, Minneapolis, Minnesota.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002531:Cerebellum / Q000166:cytology* / Q000187:drug effects; D046508:Culture Techniques; D004594:Electrophysiology; D005260:Female; D005972:Glutaminase / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D011247:Pregnancy; D011689:Purkinje Cells / Q000187:drug effects; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D051381:Rats; D013569:Synapses / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*; D013779:Tetrodotoxin / Q000494:pharmacology
D000644:Quaternary Ammonium Compounds; D005973:Glutamine; D013779:Tetrodotoxin; D005972:Glutaminase; D011188:Potassium