GAMMA-AMINOBUTYRIC ACID(A) RECEPTOR REGULATION BY A CHLORIDE-DEPENDENT KINASE AND A SODIUM-DEPENDENT PHOSPHATASE

Gamma-Aminobutyric acid(A) (GABA(A)) receptors are linked to ion chann els which mediate many aspects of neural inhibition. Although the effe cts of phosphorylation on GABA(A) receptor function have been widely s tudied, the actual role of phosphorylation in the regulation of these receptors still remains controversial. In recent reports, we have desc ribed the effects of phosphorylating/dephosphorylating enzymes on the regulation of GABA(A) receptors in a rat cortical slice preparation (S haw et al., Mol. Neuropharmacol, 2 (1992) 297-302; Shaw and Lanius, De v. Brain Res., 70 (1992) 153-161; Pasqualotto et al., Neuroreport, 4 ( 1993) 447-450) and predicted that ionic co-factors are involved in med iating the regulation of GABA(A) receptors by kinases and phosphatases . In the present report, the effects of chloride, sodium, potassium, a nd calcium were examined alone and in the presence of cAMP-dependent p rotein kinase (protein kinase A) or alkaline phosphatase. The results showed a decrease in [H-3]SR 95531 (GABA(A) receptor antagonist) bindi ng after incubation with chloride alone; this decrease was fur-ther en hanced in the presence of protein kinase A. Both effects could be bloc ked by a protein kinase A inhibitor. Conversely, an increase in [H-3]S R 95531 binding was observed after incubation with sodium alone; this increase was further enhanced in the presence of alkaline phosphatase. In both cases these increases in binding could be blocked by sodium o rthovanadate, a phosphatase inhibitor. Potassium was ineffective under all conditions; calcium showed enzyme-independent effects at low conc entrations only. These results suggest the existence of a novel chlori de-dependent protein kinase which may have significant sequence homolo gy to protein kinase A, and a novel sodium-dependent phosphatase. We s peculate that together these enzymes are responsible for the majority of the rapid regulation of cortical GABA(A) receptors in response to v arious stimuli. These data provide a link between ionic currents gener ated by ionotropic receptor activation and the resulting regulation of these receptors via activation of regulatory enzymes.