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-801 (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.