Calcification of cartilaginous matrix in culture by constant direct-current stimulation.

Forty-six femora of nine-day-old chick embryos were stimulated by 10 microA of constant direct current via platinum wire electrodes inserted into the diaphyses as cathodes in tissue culture. Apparent calcification in the hypertrophic cartilaginous region of the diaphyses was induced by the electric stimulation. This calcification was most remarkable on both ends of the diaphyses, where fine granules were observed in electron micrographs of the cartilaginous matrix. These granules were aggregates of fine needlelike crystals containing calcium and phosphorous demonstrable by X-ray microanalysis. Incorporation of 45Ca into the femora was significantly increased by the stimulation of up to 247% of the control. This matrix calcification was of interest because it occurred in avian embryonic cartilage that is normally resorbed uncalcified before it is replaced by bone.