MODULATION OF IONIC CURRENTS THROUGH GABA(A) RECEPTOR SUBTYPES BY ENDOGENOUS STEROIDS

GABA(A) receptors were expressed in Xenopus oocytes by injecting messenger RNAs from chick retina and chick cortex, and the potency of 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha-OH-DHP) and 5 alpha-pregnane-3 alpha, 21-diol-20-one (THDOC) was investigated by electrophysiology under voltage clamp conditions. For the receptors of chick retina, 3 alpha-OH-DHP (100 nM) and THDOC (100 nM) augmented GABA actions (peak current) 1.6 times (n=6) and 1.5 times (n=7), respectively. The currents induced by 0.3-10 mu M GABA for the receptors of the chick retina were sensitive to bicuculline, petobarbital, and diazepam. GABA(A) receptors in the chick retina in vivo as well as the receptors in the brain may be functionally modulated by endogenous steroids.