The high-affinity glycine transporter in neurons and glial cells is the primary means of inactivating synaptic glycine. The effects of 12-O-tetradecanoylphorbol ester (TPA), a potent activator of protein kinase C (PKC), on the high-affinity Na(+)-dependent glycine transport were investigated in C6 cells, a cell line of glial origin. Incubation of C6 cells with TPA led to concentration- and time-dependent decrease in the glycine transport that could be completely suppressed by the addition of the PKC inhibitor staurosporine. The TPA effect could be mimicked by oleoylacetylglycerol and exogenous phospholipase C. Northern and Western blot analysis indicate that C6 cells express the GLYT1 glycine transporter. Incubation of COS cells transiently transfected with a full-length clone of the GLYT1 transporter in the presence of TPA, produces a decrease in glycine uptake.