Fig. 8.

Cerebellar granule neurons maintained in either high or low K⁺ medium secrete latent TGF-β₁ and TGF-β₂. Cell-free conditioned media were transiently acidified as described in Materials and Methods, and both activated and nonactivated media were tested in triplicate for TGF-β₁ and TGF-β₂ in a quantitative sandwich enzyme immunoassay at the respective dilutions of 1:7 and 1:4. The detection limit of both immunoassays does not allow quantification of concentrations <60 pg/ml. A, Neurons grown in either low or high K⁺ concentrations produce equal amounts of latent TGF-β₁, mostly in the first 24 hr of culture, with a slight increase over time in vitro. Naturally active TGF-β₁ was not detected by the present technique. B, Neurons grown in either low or high K⁺ culture conditions release latent TGF-β₂ with a continuous production over time in culture and a major contribution by high K⁺neurons. Naturally active TGF-β₂ also was not detected.