The traditional notion that glial cells are permeable only to potassium has been revised. For example, glia from various parts of the nervous system have calcium-permeable ion channels. Since characterization of the calcium channels in glia is limited, the purpose of this study was to determine the molecular identity and examine the functional properties of a voltage-gated calcium channel expressed by Müller cells, the predominant glia of the retina. Whole-cell and perforated-patch recordings of human Müller cells in culture revealed a high threshold voltage-activated calcium current that is blocked by dihydropyridines, but not by omega-conotoxin GVIA or omega-conotoxin MVIIC. RT-PCR of cultured human Müller cells using primers specific for the calcium channel subunits demonstrated the expression of an L-type channel composed of the alpha 1D, alpha 2 and beta 3 subunits. The alpha 2 subunit of the Müller cell calcium channel is a splice variant which is distinct from either the skeletal muscle alpha 2s or the brain alpha 2b. Our electrophysiological experiments indicate that the alpha 1D/alpha 2/beta 3 calcium channel is functionally linked with the activation of a potassium channel that may serve as one of the pathways for the redistribution by Müller cells of excess retinal potassium.