Potassium exchangeability, potassium permeability, and membrane potential: Some observations in relation to protein synthesis in the early echinoderm embryo

In the sea urchin embryo the membrane potential undergoes a large hyperpolarization within 30–40 min after fertilization (from approximately −10 to −70 mV, inside negative). This is due to an increase in potassium permeability. Parallel to this is an increase in the exchangeability of internal K with the external medium, indicating an alteration in the internal compartmentalization of K. The ability of the embryos to incorporate labeled amino acid precursor into protein also increases during this period. It has been suggested that the membrane potential may regulate synthetic events within the cell. We have approached this question in the sea urchin embryo by investigating the relationships between membrane potential, membrane permeability, K compartmentalization, and protein synthesis. We have observed the following. Inhibition of the change in membrane potential by high K does not alter the ability of preloaded or pulse-labeled cells to incorporate labeled amino acid precursor. This suggests that the increase in membrane potential, per se, is not a direct regulatory factor for protein synthesis in these cells. Inhibition of the membrane potential change also does not block the decompartmentalization of intracellular K nor the increase in permeability to K. Furthermore, decompartmentalization of K is not an immediate event upon fertilization, and its gradual increase correlates in time with the increased ability to incorporate labeled precursor into protein.