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Journal of Experimental Biology 138,499-515 (1988)
Published by Company of Biologists 1988

Ion-Selectivity of Single Glutamate-Gated Channels in Locust Skeletal Muscle

K. S. KITS 1 and P. N.R. USHERWOOD 2

1 Department of Zoology, University of Nottingham University Park, Nottingham NG7 2RD, UK; Department ofBiolog, Free University, P.O. Box 7161, 1007 MC Amsterdam, The Netherlands
2 Department of Zoology, University of Nottingham University Park, Nottingham NG7 2RD, UK

The ion-selectivity of the extrajunctional glutamate-gated ion channel in locust extensor tibiae muscle was studied using the patch-clamp technique. The alkali metal ions Li+, Na+, K+, Rb+ and Cs+ were all highly permeant, with reversal potentials close to 0mV. Both complete and partial replacement of Na+ (180 mmoll-1 in standard saline) showed that conductance ({gamma}) increased in the order Li+ <Na+ < Cs+ < Rb+ (approx. 70–125 pS), {gamma}K being close to {gamma}Cs. The channel was impermeable to the large organic monovalent ions tetramethyl-ammonium, guanidinium and choline, and permeable to the smaller ammonium ion. Divalent cations (Ca2+ and Mg2+) did not contribute measurably to the ionic current. Indications were obtained that high concentrations of Mg2+ or Ca2+ block the channel. The results suggest that the glutamate-gated channel combines a high conductance with a restricted ion-selectivity, based on ion charge and size, the conductance being dependent on the dehydration energy of the ionic species.

Key words: glutamate, ion channel, ion-selectivity, patch-clamp, insect muscle

Accepted on March 10, 1988






© The Company of Biologists Ltd 1988