The ontogeny of the transepidermal potential difference in frog embryos

The potential difference across the epithelia of embryos and larvae of the frog, Xenopus laevis, has been measured using glass microelectrodes. Blastocoel stage embryos had small potentials of less than 10 mV (inside positive), a value that is within the range of tip potential error. This potential began to increase during neurulation, reaching a peak of about +60 mV by the time that spontaneous movement occurred. The potential then declined as the beginning of metamorphosis approached. A substantial fraction of the peak potential appears to be due to sodium uptake from the external medium, as is the case in the adult frog.