Ionic currents through the membrane of the mammalian oocyte and their comparison with those in the tunicate and sea urchin.

Abstract

SUMMARY1. The action potential and the membrane current of the mouse oocyte were analysed by current-clamp and voltage-clamp techniques and they were compared with those of other animal oocytes.2. The matured and unfertilized oocyte of the mouse in standard medium with 6 mM-K showed the resting potential of -23 1 + 2-9 mV. The resting potential was relatively large in the medium with 20 mM-Ca or 10 mM-Mn, being -357 + 2-6 mV and further increased to -469 + 48 mV with replacement of Na in the medium by choline.3. At the cessation of large hyperpolarization below -90 mV in standard medium, a regenerative potential was often elicited in the form of an off-response. The off-response depended upon the external concentration of Ca. In 20 mM-Ca medium it was constantly observed with hyperpolarization below -60 mV. Its critical level was -40 mV and its overshoot was +15 mV.4. The time and potential-dependent inward current was observed both in standard and 20 mM-Ca media under voltage-clamp condition. In 20 mM-Ca medium the inward current was observed by depolarization beyond -40 mV and showed its maximum at -15 mV. It was greatly reduced by replacing the external Ca with Mn but retained by substituting Sr or Ba for Ca. The selectivity ratios among these alkali earth cations were Ca: Sr: Ba = 1-0: 1-4:0-7.5. The current-voltage relation in Ca and Na-deficient and 10 mm-Mn medium was linear from -200 to +25 mV. The hyperpolarization below -200 mV revealed an inward-going rectification. The depolarization above +50 mV under voltage-clamp condition induced the outward surge current with activation and inactivation processes.6. In contrast to the mouse oocyte, the matured and unfertilized oocyte H. OKAMOTO AND OTHERS of the sea urchin showed a large resting potential of -70 mV in 30 Ca ASW and the depolarization beyond -40 mV elicited an action potential with an overshoot of 20 mV. The action potential showed a notch in the rising phase and lasted about 1 to 2 sec.7. Under the voltage-clamp condition both Ca inward current and the outward surge current were observed in the sea urchin oocyte membrane just as in the mouse oocyte membrane.8. The selectivity ratios among alkali earth cations, Ca: Sr:Ba, for 'Ca channels' of the oocyte membranes were 10:14:0-7 in the mouse, 1*0:1-7:1*1 in the tunicate and 1-0:0-7:0-5 in the sea urchin. When the current density through Ca channels are revised in terms of the respective critical levels for Ca channels, the revised selectivity sequences become Ca > Sr > Ba, being common to all three species.

Voltage-gated Ca2+ channel in mouse myeloma cells.

“…Therefore, the inactivation could not be due to the Ca2+ influx. Voltage-dependent inactivation and a selectivity where Sr2`carries the largest current have been reported also for tunicate and mouse eggs (18,19 Ca2+ channel in S194 myeloma cells are not clear at this time.…”

Bioelectric responses at fertilization: Separation of the events associated with insemination from those due to the cortical reaction in sea urchin, Lytechinus variegatus

“…These results, in conjunction with the accumulated literature, support the following conclusions: 1) The membrane potential and input resistance of the unfertilized egg are in the range of -80 mV and 300 MQ [Chambers and de Armendi, 1979; for review see Hagiwara and Jaffe, 19791, 2) voltage depolarizations of about 10 mV at the approximate moment of sperm-egg fusion, which shortly follows sperm attachment and is independent of sperm incorporation, 3) an action potential that is fired when this depolarization reaches its threshold level [Okamoto et al, 1977;Chambers and de Armendi, 1979],4) the Na+-dependent membrane potential reversal that precedes the secretion of the cortical granules [Steinhardt et al, 19711 and associated capacitance changes [Jaffe et al, 19781, and 5) the repolarization of the egg membrane associated with increased K' conductance and egg activation Shen and Steinhardt, 19801. A model in which sperm-egg fusion results in a minor electrical transient [DeFelice and Dale, 19791 and triggers the secretion of the cortical granules, which results both in the Na+-dependent fast block to polyspermy [Jaffe, 19761 and the late block due to the secreted contents of the cortical granules (Vacquier et al, 1972), is proposed.…”

“…The early changes include an action potential [Okamoto et al, 1977;Chambers and de Armendi, 19791 and a Na+-dependent reversal of the membrane potential [Steinhardt et al, 19711, which both together may be responsible for the fast block to polyspermy [Jaffe, 19761. The repolarization of the membrane is accompanied by an increase in K+-conductance and by intracellular changes in [Ca++], which trigger the metabolic activation of the egg [Steinhardt et al, 1971;Grainger et al, 1979;Steinhardt and Winkler, 1979;Shen and Steinhardt, 1980;Winkler et al, 19801.…”

From Nutrition to Health: The Role of Natural Products – A Review

“…Many cellular functions, such as electrical signal generation in nerve and muscle cells, contraction in muscle cells, and secretion in nerve and gland cells depends on the significant role of widely distributed voltage-dependent calcium channels (Hagiwara, 1983;Hagiwara and Byerly, 1981). They exist not only in fully differentiated cells but also already in oocytes (Okamoto et al, 1977) and in developing nerve and muscle cells (Spitzer, 1979). There are several reports that calcium channels are restricted to, or more prominent in, the less differentiated states of excitable cells such as skeletal cells (Kano, 1975;Kidokoro, 1973;Kidokoro, 1975) and nerve cells (Matsuda et al, 1978;Mori-Okamoto et al, 1983;Spitzer and Baccaglini, 1976).…”