AGE-DEPENDENT CHANGES IN THE REGULATION BY EXTERNAL CALCIUM-IONS OF THE PHOSPHORYLATION OF GLIAL FIBRILLARY ACIDIC PROTEIN IN SLICES OF RATHIPPOCAMPUS

We studied the effect of external Ca2+ on the incorporation of [P-32]p hosphate into the astrocytic marker protein, glial fibrillary acidic p rotein (GFAP), in hippocampal slices from rats in the postnatal age ra nge 12-16 days to +60 days (P12-P16 to +P60). At age P12-P16 the prese nce of Ca2+ in the incubation medium inhibited the incorporation of P- 32 into GFAP; this inhibition declined to near zero by P21 and subsequ ently P-32-incorporation became progressively more dependent on Ca2+ u ntil by P60 no GFAP phosphorylation was observed in the absence of Ca2 +. With tissue from immature rats inhibition of P-32-incorporation int o GFAP started at a medium concentration of 7.5 mu M Ca2+, reached 50% at 100 mu M and then remained constant up to 1 mM; with adults maxima l phosphorylation required 1 mM Ca2+ in the medium. The inorganic Ca2-channel blockers, Co2+ and Ni2+, and, high concentration of the L-typ e blocker, nifedipine, reversed the effects of external Ca2+ on GFAP p hosphorylation. The results suggest a late developmental change in the compartmental disposition of Ca2+ in astrocytes.