Environmental enhancement of in vitro chondrogenesis. 3. The influence of external potassium ions and chondrogenic differentiation

A simple manipulation, altering the potassium concentration of the nutrient medium, has a pronounced effect upon the in vitro chondrogenic differentiation of chick somites, as measured by chondroitin sulfate synthesis and cartilage formation. Medium containing K⁺ ions in the balanced salt solution at a concentration of 2.69 mM promotes chondrogenesis over the 48-hr period studied. By increasing the K⁺ concentration to 4.68 mM there is a striking enhancement of initial chondroitin sulfate synthesis during the first 24 hr only. If the somite explants in a high K⁺ environment are transferred after 24 hr to a lower K⁺ concentration, the chondrogenic stimulation (chondroitin sulfate synthesis) continues. These effects can be obtained by altering only one variable in the nutrient medium, the K⁺ concentration.