Facilitatory coupling between a glutamate metabotropic receptor and dihydropyridine-sensitive calcium channels in cultured cerebellar granule cells.

The effect of metabotropic glutamate receptor activation on Ca dihydropyridine (DHP)-sensitive channels recorded in the presence of 1 microM Bay K 8644 was examined on cultured cerebellar granule cells using the patch-clamp technique in the cell-attached configuration. Bath-applied agonist (trans-ACPD, 1S,3R-, and 1R,3S-ACPD isomers, and glutamate or quisqualate in the presence of CPP and CNQX) evoked an increase in Ca channel activity with a variable latency of 8.9 +/- 8.6 sec in 40% of the recorded cells. Neither L-CCG1, L-AP3, L-AP4, nor AMPA or NMDA activated Ca channels. Two dihydropyridine-sensitive channels present in this cell type were activated by trans-ACPD: the classical 24 pS L-type channel and a smaller-conductance 7 pS channel. The effect was shown to be mediated by neither intracellular Ca2+ nor a pertussis toxin (PTX)-sensitive G protein. Interestingly treatment with BAPTA-AM increased the number of responding patches and the activity was more sustained throughout the drug application. After overnight PTX treatment, activation of the Ca channels persisted even after washout of the agonist. These results indicate that mGluR1/mGluR5 probably mediate the facilitation of dihydropyridine-sensitive Ca channels.