Glycine-activated whole cell and single channel currents in rat cerebellar granule cells in culture.

The patch clamp technique was used to study whole cell and single channel currents evoked by glycine in cerebellar granule cells in culture. Whole cell concentration response curve gave a Kd value for glycine of 73 microM and a Hill slope of 1.58. Glycine-activated currents reversed close to the predicted Cl- equilibrium potential. The responses to glycine were antagonized by strychnine and picrotoxin with an IC50 of 58 nM and 172 microM, respectively. Furthermore, glycine-evoked currents were potentiated by zinc in a dose-dependent way. In outside-out membrane patches, glycine opened channels with conductances of 32, 52, 84 and 96 pS. The most frequently occurring was the 52 pS channel. The single channel current/voltage relationship was linear in the potential range between -60 and 60 mV. The 52, 84 and 96 pS channels exhibited prolonged openings whereas the 32 pS was characterized by fast (< 10 ms) openings. Open and closed time histograms of the 52 pS channel could be fitted with the sum of two or three exponentials, respectively, whereas burst duration histograms could be fitted with the sum of two exponentials. Glycine current density change drastically during days in culture, the maximal expression being between day 4 and 7, suggesting that the expression of glycine receptor channels is developmentally regulated.