Involvement of phosphatase activities in the run-down of GABA(A) receptor function in rat cerebellar granule cells in culture.
Run-down of GABA activated Cl- currents was found when rat cerebellar granule cells in culture were studied by the whole-cell patch-clamp technique in the absence of ATP in the pipette medium. This event could be prevented, even in the absence of ATP, by using the perforated-patch technique or by adding to the pipette medium either a blocker of protein tyrosine phosphatase, sodium vanadate, or deltamethrin, a blocker of the protein serine/threonine phosphatase calcineurin. Conversely, run-down could be partially induced, even in the presence of ATP, by blockers of tyrosine kinases. A reduction of GABA(A) receptor activity was also found in outside-out membrane patches when ATP was not on the membrane inside. The run-down phenomenon involved all three conductance levels found in these patches: 11, 20 and 30 pS. In all three cases it was due to a reduction of channels' open probability. The single-channel experiments showed that also in this case run-down was prevented by either sodium vanadate or deltamethrin on the membrane cytoplasmic side. Overall, through relatively unphysiological conditions (cells in culture and patch-clamp techniques), the study of the run-down phenomenon shows that the tyrosine phosphorylation state of GABA(A) receptors is of importance in maintaining it in a proper functional state. The data also show that tyrosine phosphorylation state is controlled by a protein tyrosine phosphatase, whose activity in turn is blocked via serine/threonine phosphorylation.
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I.N.F.M., Dipartimento di Fisica dell'Università di Genova, Italy.
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D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000502:physiology*; D018118:Chloride Channels / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009570:Nitriles; D011722:Pyrethrins / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014638:Vanadates / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D018118:Chloride Channels; D009570:Nitriles; D011722:Pyrethrins; D011963:Receptors, GABA-A; C017180:decamethrin; D014638:Vanadates; D005680:gamma-Aminobutyric Acid; D000255:Adenosine Triphosphate