Uptake of chlorotetracycline into mouse eggs.

The fluorescent compound chlorotetracycline (CTC) enters the mouse egg by a mechanism controlled by the oolemma. The intracellular distribution of CTC is non-uniform and during the early stages of uptake fluorescent patches are observed at the egg's surface probably close to the oolemma. Lanthanum blocks the entry of CTC into the egg's cytoplasm and in this condition the CTC remains at the surface of the egg; the labelled site is not the zona pellucida and is likely to be the outer surface of the oolemma. The results of this study of CTC uptake support the idea that this compound labels divalent (or trivalent) cations in the neighbourhood of cell membranes.