Figure 8.
Uptake of 42K in cultured cerebral astrocytes and neurons (the GABAergic cortical interneurons) at 37°C as a function of time of exposure to the isotope during incubation in tissue culture medium with 5.4 mM K+ (same concentration as during the culturing). Uptake into the astrocytes was measured both at steady state (i.e., cells obtained directly from the incubator and only exposed to medium change and radio-isotope addition), where it includes channel-mediated homoexchange, and in cells depleted for intracellular K+ during previous incubation in ice-cold K+-free medium, where all uptake above an intracellular concentration of 5.4 mM must be active. Uptake into neurons was only measured at steady state, since their K+ permeability at a K+ concentration of 5.4 mM is negligible. From Hertz (1986).