The muscarinic modulation of [ 3 H] d -aspartate efflux and [Ca 2+ ] i levels in rat cerebellar granule cells

The effects of ACh on [ 3 H] d -aspartate efflux and on calcium levels ([Ca 2+ ] i ) were studied at the same time in sister cultures of rat cerebellar granule cells stimulated with electrical pulses (5–20 Hz) or depolarized with KCl (15–40 mM). ACh, 0.3–1000 nM, greatly facilitated the 10-Hz-evoked tritium efflux while its effect on 20 mM KCl-evoked efflux was significantly smaller. ACh, 10–1000 nM, enhanced [Ca 2+ ] i levels to a limited extent under both experimental conditions. Therefore, ACh facilitation was evident above all on the electrically evoked [ 3 H] d -aspartate efflux. The ACh-mediated responses depended on the activation of M 3 -muscarinic receptors since these responses were blocked by 4-DAMP. ACh, 50 μM, reduced the [Ca 2+ ] i plateau, determined by prolonged electrical or KCl stimulation. This effect was due to its action of M 2 -receptors being blocked by AF-DX 116. In conclusion, at very low concentrations, ACh greatly facilitated the electrically evoked [ 3 H] d -aspartate efflux through M 3 -receptors, while at a higher concentrations, it inhibited, through M 2 -receptors, the rise in [Ca 2+ ] i caused by prolonged cell depolarization.