Interaction between copper and zinc at GABA(A) receptors in acutely isolated cerebellar Purkinje cells of the rat.
Nanomolar concentrations of Cu(2+) induce a slowly reversible block of GABA(A) receptor-mediated currents which can be removed by chelating substances. The possible interaction of Cu(2+) with the Zn(2+) binding site on the GABA(A) receptor complex was studied in acutely isolated Purkinje cells using whole-cell recording and a fast drug application system. When Zn(2+) was applied together with 2 microM GABA, the Zn(2+)-induced block of GABA-mediated currents was not additive to the Cu(2+)-induced block. In the presence of 0.1 microM Cu(2+) in the bath solution the degree of inhibition of GABA-mediated responses by Zn(2+) was strongly attenuated. Preapplication of 100 microM Zn(2+) during 10 s, terminated 1 s before exposure to 2 microM GABA did not affect the GABA current in Cu(2+)-free solution, but relieved its block by 0.1 microM Cu(2+). This effect of Zn(2+) was concentration-dependent with an EC(50) of 72 microM. When the Cu(2+)-induced block was removed by histidine, preapplication of Zn(2+) did not increase the GABA current, indicating that the relief of Cu(2+) block by Zn(2+) is the result of its ability to actively remove Cu(2+) from the GABA receptor complex. It is proposed that the inhibitory effects of Zn(2+) and Cu(2+) on GABA-induced currents result from an action of these metal ions at distinct, but conformationally linked sites on the GABA(A) receptor protein. Under physiological conditions Zn(2+) would liberate Cu(2+) from the GABA(A) receptor, thus facilitating Cu(2+) turnover and its binding by other endogenous chelating molecules.
Sharonova
I N
IN
Brain Research Institute, Russian Academy of Medical Sciences, Moscow, Russia.
Vorobjev
V S
VS
Haas
H L
HL
D000818:Animals; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D003300:Copper / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011689:Purkinje Cells / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000502:physiology; D015032:Zinc / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D003300:Copper; D015032:Zinc