FERTILIZATION CURRENT IN THE HUMAN OOCYTE

In this report we show that the first event of activation in the human oocyte, the Fertilization current (FC), is a slow transient outward c urrent of 300 pA, which induces a gradual hyperpolarization of the pla sma membrane from -20mV to -60mV, 60-120 min after insemination, follo wed by a repolarization to -20mV. Activation currents (AC) of 600-2,50 0 pA, induced by exposure to the calcium ionophore A23187 or by microi njection of InsP(3) into the cytosol, are also outward. The AC are inh ibited by preloading oocytes with EGTA suggesting they are calcium dep endent. Since AC are 2-10-fold the amplitude of the FC the fertilizing spermatozoon in the human only activates a portion of the primary ele ments stored in the oocyte for triggering metabolic depression. Oocyte activation in the human resembles that in the hamster rather than oth er mammals or invertebrates studied to date. (C) 1994 Wiley-Liss, Inc.