UP-REGULATION OF NR2B SUBUNIT OF NMDA RECEPTORS IN CEREBELLAR GRANULENEURONS BY CA2+ CALMODULIN KINASE INHIBITOR KN93/

Recordings of NMDA-activated currents from cerebellar granule neurons in culture revealed a developmental increase in current density accomp anied by a slight decrease of the half-maximal effective concentration . At the same time, a decrease of NMDA receptors comprising NR2B subun its was demonstrated by the reduction in the antagonism of NMDA curren ts by ifenprodil. Ifenprodil antagonism increased after treatment for 24 h with KN93- and KN62-selective inhibitors of the Ca2+/calmodulin-d ependent protein kinases (CaM kinases), indicating a selective increas e of receptor containing NR2B subunit. This increase was observed at a ll ages tested: 4 days in vitro (DIV4), DIV6, and DIV13. Western blot analysis with specific NMDA receptor antibodies performed at DIV6 conf irmed the electrophysiological data. At this age, the negative control KN92 was ineffective. The increasing ifenprodil antagonism after KN93 treatment was proportionally greater in cells at DIV13 than at DIV4. Treatment with NMDA (100 mu M) of cerebellar cultures for 24 h produce d a decrease in the NMDA-induced current density by almost 50% at all ages tested. Ifenprodil antagonism, however, was unchanged. We propose that the expression of NR2B subunits in cerebellar granule cells is s electively stimulated by the inhibition of CaM kinases.