Journal of Neurophysiology, Vol 76, Issue 1 227-241, Copyright © 1996 by APS

ARTICLES

Glycine current in rat septal cholinergic neuron in culture: monophasic positive modulation by Zn2+

E. Kumamoto and Y. Murata
Department of Physiology, Saga Medical School, Japan.

1. Membrane currents induced by glycine (Iglys) were investigated in cholinergic neurons in primary culture, isolated from the septal region of fetal rat brains, by use of the whole cell voltage-clamp recording configuration. A glycine response was observed in 131 of 150 neurons examined. 2. Igly was accompanied by an increase in conductance and reversed the direction at the Cl- equilibrium potential. The Igly-voltage relation was a little outwardly rectifying in a range of -40 to +30 mV in a nearly symmetrical Cl- solution system. 3. Glycine applied by local perfusion produced an Igly, which increased in amplitude sigmoidally with increasing concentrations (EC50 = 110 microM; nH = 1.75) and desensitized at higher concentrations. There was no nondesensitizing component in Igly (100 microM). Strychnine inhibited Igly in a dose-dependent and competitive manner; it took at most 1 min for this action to be attained to a steady level. Schild analysis yielded the dissociation constant for strychnine to be 0.062 microM. Igly was depressed noncompetitively by a gamma-aminobutyric acid-A (GABAA) receptor-channel blocker, picrotoxin, in a dose-dependent manner (IC50 = 45 microM for peak Igly at 100 microM). On the contrary, another GABAA inhibitor, bicuculline (10 microM), did not affect Igly. 4. Igly was unaffected by spermine (1 mM), ethanol (1-100 mM), and diazepam (1 microM) and was depressed by 14% by pentobarbital (100 microM). On the other hand, Zn2+ potentiated Igly in a dose-dependent (EC50 = 9.1 microM; nH = 1.3; 38% increase for Igly at 50 microM by 100 microM Zn2+) and reversible manner. The facilitatory action was due to an increase in the apparent affinity for glycine (by 139% by 100 microM Zn2+), and did not depend on holding potentials. Pb2+ (100 microM) and La3+ (100 microM) also enhanced Igly (50 microM) by 23 and 14%, respectively; these actions were abolished in the presence of Zn2+ (100 microM). Igly was not affected by Ba2+, Sr2+, Co2+, Mn2+, Cd2+, and Al3+ (100 microM each). 5. Rat septal cholinergic neurons in culture were endowed with a Cl(-)-selective glycine receptor channel whose activation was sensitive to strychnine and picrotoxin. Zn2+ induced a positive modulation of the glycine response, possibly through an allosteric interaction with the glycine-binding site; this action was shared by Pb2+ and La3+ with a potency sequence of Zn2+ > Pb2+ > La3+. This metal-ion binding site could serve to enhance a glycine action.

This article has been cited by other articles:

				M. Beato, V. Burzomato, and L. G. Sivilotti The kinetics of inhibition of rat recombinant heteromeric {alpha}1beta glycine receptors by the low-affinity antagonist SR-95531 J. Physiol., April 1, 2007; 580(1): 171 - 179. [Abstract] [Full Text] [PDF]

				J. W. Lynch Molecular Structure and Function of the Glycine Receptor Chloride Channel Physiol Rev, October 1, 2004; 84(4): 1051 - 1095. [Abstract] [Full Text] [PDF]

				S. C. Chattipakorn and L. L. McMahon Pharmacological Characterization of Glycine-Gated Chloride Currents Recorded in Rat Hippocampal Slices J Neurophysiol, March 1, 2002; 87(3): 1515 - 1525. [Abstract] [Full Text] [PDF]

				H. Suwa, L. Saint-Amant, A. Triller, P. Drapeau, and P. Legendre High-Affinity Zinc Potentiation of Inhibitory Postsynaptic Glycinergic Currents in the Zebrafish Hindbrain J Neurophysiol, February 1, 2001; 85(2): 912 - 925. [Abstract] [Full Text] [PDF]

				Y. Han and S. M. Wu Modulation of glycine receptors in retinal ganglion cells by zinc PNAS, March 16, 1999; 96(6): 3234 - 3238. [Abstract] [Full Text] [PDF]

				T. P. Harty and P. B. Manis Kinetic Analysis of Glycine Receptor Currents in Ventral Cochlear Nucleus J Neurophysiol, April 1, 1998; 79(4): 1891 - 1901. [Abstract] [Full Text] [PDF]