N-methyl-D-aspartate receptor-mediated spontaneous activity in cerebellar granule cells in culture

An outside-out configuration of the patch-clamp method was used to study the properties of spontaneous and glutamate-evoked single channel activity in cerebellar granule cells in culture. Both spontaneous occurring events and glutamate-evoked single channel currents had similar conductances (17.7, 36.5; 17.3, 35.8 pS) and mean open times (0.7, 7.1; 0.6, 7.8 ms). In magnesium free solution, the spontaneous channels were blocked by the NMDA-receptor antagonist APV (0.1 mM) and by the NMDA-channel blocker MK-80 (0.1 mM). The spontaneous activity disappeared at negative holding potentials when the bathing solution contained magnesium (5 mM). Maximum conductance of spontaneous channels increased with days in culture (DIC) from 9 pS at 1 DIC to 59 pS at 10 DIC. These experiments suggest that endogenous transmitter activates NMDA-receptors in cerebellar granule cells in culture.