Stimulation of 36Cl- permeation in the in----out direction across the Dieters' neuron membrane by GABA on its cytoplasmic side: effect of different ionic conditions.
The permeation of labelled Cl- ions across single plasma membranes microdissected from rabbit Deiters' neuron was studied in a microchamber system. In particular, we studied 36Cl- in----out permeation and its stimulation by 10(-6) M GABA on the cytoplasmic side under different ionic conditions on both sides of the membrane. Three main results were found: a) The GABA effect turns up at a cytoplasmic side [Cl-], 21 mM, in the range of the normal steady state intracellular Cl- concentration. It disappears both at tracer level of Cl- on the cytoplasmic side and when [Cl-] is high there (140 mM). b) The increase in ionic strength due to the equinormal substitution of monovalent anions (Cl- and acetate) with the trivalent impermeant anion citrate on both sides of the membrane erases the GABA effect even if Cl- is at the optimal cytoplasmic side concentration, 21 mM. c) Citrate ions reduce to the limit of significance the GABA effect even when they are only on the membrane extracellular side and [Cl-] is at the optimal level on the other side. These results confirm that GABA stimulated Cl- permeation in the in----out direction is via Cl- channels exposing positive charges at their cytoplasmic mouth. In addition, they point out that such GABA activated channels are endowed with a partial electrical positivity at their extracellular exit.
Rapallino
M V
MV
Centro di Neurofisiologia Cerebrale, C.N.R., Genova, Italy.
Cupello
A
A
Hydén
H
H
D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D002713:Chlorine; D002951:Citrates / Q000494:pharmacology; D019343:Citric Acid; D003593:Cytoplasm / Q000378:metabolism*; D007477:Ions; D009474:Neurons / Q000378:metabolism*; D011868:Radioisotopes; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002712:Chlorides; D002951:Citrates; D007477:Ions; D011868:Radioisotopes; D019343:Citric Acid; D002713:Chlorine; D005680:gamma-Aminobutyric Acid