Pharmacological characterisation of voltage-sensitive calcium channels and neurotransmitter release from mouse cerebellar granule cells in culture.

Using subtype-specific Ca-channel blockers, we have characterised the voltage-sensitive Ca2+ currents as well as neurotransmitter release from cultured mouse cerebellar granule cells. The whole cell version of the patch clamp technique was adapted to monitor the isolated Ca-channel currents. The currents were activated at potentials more positive than -40 mV and were composed of at least four pharmacological distinct components being sensitive to nifedipine (35%), omega-conotoxin GVIA (10%), and omega-agatoxin IVA (42%) corresponding to L-, N-, and P-channel-mediated currents. The insensitive fraction (13%) possibly represented R channels. High potassium-evoked release of 3H-D-aspartate was used as a model of synaptic release. These studies were performed at relatively mild stimulation conditions (30 mM K+, 0.4 mM Ca2+), and 85% of the evoked release was Ca2+ dependent as well as tetrodotoxin and Cd2+ sensitive. Nifedipine and omega-agatoxin IVA dose dependently (IC50 values of 10 nM and 0.7 nM, respectively) blocked most of the release, whereas omega-conotoxin MVIIA (IC50 = 5 nM) caused partial blockage. The results indicate that several subtypes of voltage-sensitive Ca channels are present in mouse cerebellar granule cells. Furthermore, the data suggest that L, N, and P channels act in concert in the neurotransmitter release process.