Changes in excitability of the cell membrane during 'differentiation without cleavage' in the egg of the annelid, Chaetopterus pergamentaceus.

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Abstract
The egg of the polychaete C. pergamentaceus, differentiates parthenogenetically without cleavage after 1 h in a high K+ solution. Changes in the electrical properties of the membrane during differentiation were investigated. The treatment with the K solution for 40-60 min made unfertilized eggs become amoeboid cells in 4-5 h and finally ciliated unicellular embryos in 14-16 h. In the untreated egg the action potential is Ca dependent and no Na component is found. The steady-state current-voltage relation has a marked inward rectification and shows a less marked outward rectification. There are no significant changes in these properties of the cell membrane immediately after 40-60 min K treatment. In the amoeboid cell stage (4-5 h) the outward rectification increases significantly. In the ciliated unicellular embryo the action potential is Ca and Na dependent. Probably, Ca channels are present in the egg initially, K channels appear next and Na channels appear later.