Ouabain-sensitive and ouabain-resistant net uptake of potassium into astrocytes and neurons in primary cultures

Abstract

Inhibition of net uptake of 42K by different concentrations of ouabain was studied in primary cultures of astrocytes and in primary cultures of neurons in order to investigate whether there is a pronounced difference between ouabain sensitivity in the two cell types and to determine the genuine magnitudes of the ouabain-sensitive and the ouabain-resistant potassium uptakes. In morphologically differentiated astrocytes, obtained after treatment with dibutyryl cyclic AMP (dBcAMP), the sensitivity to ouabain was slightly lower than in neurons, but astrocytes which had not been treated with dBcAMP showed sensitivity similar to the neurons (which likewise were not treated). In the presence of elevated potassium concentrations (12 and 24 mM) ouabain sensitivity was decreased, although only by a factor of 2-3. Accordingly, maximum inhibition of the uptake required under all conditions studied, at most, 1.0 mM ouabain. Like total uptake, this ouabain-sensitive uptake was several times less intense in neurons than in astrocytes, where it reached its maximum value at an external potassium concentration of 12 mM. Subtraction of the ouabain-sensitive uptake from the total uptake revealed a considerable ouabain-resistant uptake. This ouabain-resistant uptake was studied in detail in the astrocytes, where it was found to increase with increasing potassium concentration over the whole concentration range 3-24 mM and to exceed substantially the maximum amount that can be accumulated by diffusion.