Actions of Zn2+ on spontaneous, stimulus and transmitter evoked events in Helix neurons.
Modulatory actions of Zn2+ (0.05-2 mM) on spontaneous, stimulus evoked excitatory postsynaptic potentials (EPSPs) or currents (EPSCs) and GABA, L-glutamate induced depolarizations were examined in current- and voltage-clamp conditions. Identified and unidentified Helix pomatia L. neurons were used in the experiments. Zn2+ increased the frequency of the spontaneous EPSPs or EPSCs in a dose-dependent manner but the excitation slowly declined with time. Two phasic effects of Zn2+ on stimulus evoked EPSPs or EPSCs were characteristic in both normal and low Ca(2+)-high Mg2+ salines. Zn2+ in a low dose (0.05-0.4 mM) increased, but in a higher dose decreased the amplitude of the evoked EPSP or EPSCs. Higher than 1 mM Zn2+ sustained the voltage dependence of the stimulus evoked EPSPs or EPSCs. Sodium-potassium dependent depolarizations of GABA and glutamate responses were attenuated by zinc ions. The zinc ion sensitivity of neurons derived from active animals was higher then of hibernating species (IC50 = 0.73 +/- 0.006; 1.33 +/- 0.12, respectively, mean +/- SEM, n = 12). We conclude that zinc ions have both pre- and post-synaptic effects. Zinc induced actions on Helix neuronal synapses based on the modulation of a complex phenomenon appear to be more than one mechanism.
Kovács
T
T
Department of Comparative Physiology, Attila József University of Sciences, Szeged, Hungary.
Erdélyi
L
L
D000818:Animals; D005071:Evoked Potentials / Q000187:drug effects; D018698:Glutamic Acid / Q000494:pharmacology; D006372:Helix, Snails / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D015032:Zinc / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D015032:Zinc