ENHANCEMENT OF VOLTAGE-GATED CA2-NEURONS WITH GLUTAMATE( CURRENTS INDUCED BY DAILY STIMULATION OF HIPPOCAMPAL)

The regulation of calcium channel currents (I-Ca) induced by daily sti mulation (1 hr) with 10 mu M glutamate was studied in full differentia ted hippocampal cells in culture. We report a specific enhancement of the high-voltage-activated current type (HVA I-Ca) ongoing over days. The density of HVA I-Ca increased about twofold after the second gluta mate session, and this enhancement was still observed after the fifth day of treatment, while low-voltage-activated calcium currents (LVA I- Ca) remained unchanged. During glutamate application, a transient incr ease of intracellular calcium (Ca-i) was observed, followed by a slow decay within 2-3 min, and substantial recovery in about 10 min. Simila rly, Ca-i transients induced by periodic membrane depolarization mimic ked the long-term effect of glutamate on I-Ca. These results demonstra te for the first time an increase of I-Ca in a time frame of days. Sin ce the effect of glutamate on I-Ca was prevented by cycloheximide, neo synthesis of channel proteins presumably supports this enhancement.