Chloride channels gated by extrajunctional glutamate receptors (H-receptors) on locust leg muscle.
Outside-out patches of extrasynaptic membrane were isolated from leg muscles of locusts. L-Glutamate and its agonists were applied to such patches either continuously or in rapidly switched pulses. When the pipette contained a high chloride concentration, 2.5 x 10(-5) M glutamate triggered single-channel currents (gated by H-receptors) with a conductance of 25 pS which were carried by chloride, in addition to cationic channels (gated by D-receptors). For the chloride channels, the distribution of channel open times had components of about 2 and 12 ms. Pulses of higher glutamate concentrations elicited many superimposed channel openings, and the approximately saturating concentration of 10(-3) M glutamate opened 100-200 channels simultaneously. When the pipette contained low chloride, channel conductance was reduced, and the current voltage relation was shifted towards the now negative chloride equilibrium potential. H-Receptor-gated chloride channels were activated by glutamate, ibotenate and aspartate, but not by GABA, quisqualate, kainate, N-methyl-D-aspartate and carbachol. The currents declined in the continued presence of agonist showing a time constant of desensitization greater than 1 s. Recovery from desensitization after removal of the agonist was tested with double pulses and was found to have a time constant of about 300 ms.
Dudel
J
J
Physiologisches Institut der Technischen Universität München, F.R.G.
Franke
C
C
Hatt
H
H
Usherwood
P N
PN
D000818:Animals; D002712:Chlorides / Q000502:physiology*; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D006110:Grasshoppers / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials; D009132:Muscles / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000502:physiology*
D002712:Chlorides; D005971:Glutamates; D007473:Ion Channels; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D018698:Glutamic Acid