The role of glial cells in regulation of neurotransmitter amino acids in the external environment. I. Transmembrane electrical and ion gradients and energy parameters in cultured glial-derived cell lines.

Studies of energy parameters and intracellular ion concentrations were carried out on two glial cell lines, one derived from an astrocytoma (C6) and the other from an oligodendroglioma (TR33B), to elucidate the mechanism of transport of amino acid neurotransmitters by glial cells. Respiratory rate was 2.7-2.9 nmol/min/mg dry wt.; cytochrome c at 0.035-0.041 nmol/mg dry wt., was 23-29% reduced with a calculated turnover number 4.7-5.1 e-/s at 23 degrees C. ATP levels were high, 5.0-6.5 mM and [CrP]/[Cr] was almost 2. Membrane potentials at [K+]e = 5 mM were approximately -90 mV for C6 cells and -72 mV for TR33B. [K+]i was measured as approximately 100 mM for TR33B and 150 mM for C6 which indicated that the K+ diffusion potential was the major source of the membrane potential. [Na+]i was 5.8 mM for C6 and 20 mM for TR33B cells while free calcium was about 100 nM in both. Near Nernstian relationships were found in both types of cell between [K+]e and membrane potential over a range of 3.5-75 mM for TR33B and 5-110 mM for C6 cells. It is concluded that C6 and TR33B cell lines may be useful models for in vitro studies of some aspects of glial behavior.