IS PROTEIN-KINASE-C ACTIVITY REQUIRED FOR THE N-METHYL-D-ASPARTATE-EVOKED RISE IN CYTOSOLIC CA2+ IN MOUSE STRIATAL NEURONS

The present study investigates the roles of protein kinase C (PKC) and A (PKA) activities in NMDA-mediated Ca2+ entry in primary cultures of mouse striatal neurons. Inhibitors of protein kinases, such as sphingosine, RO 31 - 8220 and staurosporine inhibited the NMDA- but also the KCl-induced rise in cytosolic Ca2+. However, the PKA antagonist Rp-adenosine-3',5'monophosphothioate (Rp-cAMPS) did not alter the NMDA + D-serine response, whereas it completely suppressed the KCl response. The NMDA + D-serine-evoked rise in cytosolic Ca2+, observed in the absence of external Mg2+, was potentiated by the PKC activator phorbol 12-myristate 13-acetate (PMA) only when submaximal effective concentrations of this agonist and co-agonist were used. In addition, the PKC activator did not alter the NMDA + D-serine-evoked response in the presence of varying concentrations of Mg2+. Confirming the dependence on PKC activity, desensitization of PKC resulting from longterm PMA treatment led to an impairment of the NMDA response, leaving the KCl-induced response intact. We therefore propose that PKC not only potentiates but is also required for the NMDA-evoked elevation in cytosolic Ca2+ in mouse striatal neurons.