The interactions between plasma membrane depolarization and glutamate receptor activation in the regulation of cytoplasmic free calcium in cultured cerebellar granule cells

Abstract

The complex modulation of cytoplasmic free calcium concentration ([Ca2+]c) in primary cultures of cerebellar granule cells in response to glutamate receptor agonists has been the subject of several contradictory reports. We here show that 3 components of the [Ca2+]c response can be distinguished: (1) Ca2+ entry through voltage-dependent Ca2+ channels, following KCl- or receptor-evoked depolarization, (2) Ca2+ entry through NMDA receptor channels, and (3) liberation of internal Ca2+ via a metabolotropic receptor. Depolarization with KCl induced a transient [Ca2+]c response (subject to voltage inactivation) decaying to a sustained plateau (largely inhibited by nifedipine). The NMDA response was potentiated by glycine, totally inhibited by (+)5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801), and blocked by Mg2+ in a voltage-sensitive manner. Polarized cells displayed small responses to quisqualate (QA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA). Depolarization enhanced a transient response to QA, but not to AMPA. Trans-1-amino-1,3-cyclopentanedicarboxylic acid (trans-ACPD), a selective agonist for the metabolotropic glutamate receptor, caused a transient elevation of [Ca2+]c, which was blocked by prior exposure to QA but not AMPA. The prolonged [Ca2+]c response to kainate (KA) can be resolved into 2 major components: an indirect NMDA receptor-mediated response due to released glutamate and a nifedipine-sensitive component consistent with depolarization-mediated entry via Ca2+ channels. 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX), QA at greater than 10 microM, and AMPA (but not trans-ACPD) reversed the KA response, consistent with an inactivation of the KA receptor.(ABSTRACT TRUNCATED AT 250 WORDS)