Differential regulation by pregnenolone sulfate of intracellular Ca2+ increase by amino acids in primary cultured rat cortical neurons.
We investigated the effects of pregnenolone sulfate (PS) on the [Ca2+]i increase induced by gamma-aminobutyric acid (GABA) and N-methyl-D-aspartate (NMDA) using fluorescence imaging. PS inhibited the 50 microM GABA-induced increase in [Ca2+]i in a dose-dependent manner with an IC50 of 30 microM. The inhibitory effect of PS was apparent within 5 min and was in a non-competitive manner, suggesting that PS may act directly to the membrane level but indirectly to the GABA binding sites. Our previous study has already shown that the GABA-induced Ca2+ increase involves GABAA receptors and the similar pathway to a high K(+)-induced Ca2+ response (Takebayashi et al., 1996). Because 50 microM of PS could not inhibit a 25 mM K(+)-induced Ca2+ increase, it seems likely that the site of the inhibitory action of PS on the GABA-induced Ca2+ increase may be independent of the pathway of the high K(+)-induced Ca2+ response, but rather at GABAA receptor complex. In contrast, PS potentiated the 50 microM NMDA-induced increase in [Ca2+]i in a dose-dependent manner. The magnitude of the NMDA response was approximately doubled in the presence of 100 microM of PS. However, PS did not affect the acetylcholine(Ach)-induced increase in [Ca2+]i. Furthermore, corticosterone had little effect on the GABA- and NMDA-induced Ca2+ increases, indicating that the alteration of the Ca2+ response is specific for PS. In conclusion, it is suggested that PS modulates differentially [Ca2+]i increase induced by GABA and NMDA.
Takebayashi
M
M
Department of Psychiatry and Neurosciences, Hiroshima University School of Medicine, Japan.
Kagaya
A
A
Uchitomi
Y
Y
Yokota
N
N
Horiguchi
J
J
Yamawaki
S
S
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D004622:Embryo, Mammalian; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011284:Pregnenolone / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D011963:Receptors, GABA-A; C018370:pregnenolone sulfate; D005680:gamma-Aminobutyric Acid; D016202:N-Methylaspartate; D011284:Pregnenolone; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium