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Periodic hyperpolarizing responses in hamster and mouse eggs fertilized with mouse sperm
Author(s) -
Igusa Yukio,
Miyazaki ShunIchi,
Yamashita Naohide
Publication year - 1983
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1983.sp014784
Subject(s) - hamster , sperm , insemination , biology , egta , golden hamster , andrology , gamete , mesocricetus , anatomy , chemistry , endocrinology , medicine , genetics , calcium
1. The zona‐free hamster egg allows multiple entries of heterologous as well as homologous sperm. The hamster egg inseminated with mouse sperm (M × H egg) showed recurring, transient hyperpolarizing responses (h.r.s) with the peak of ‐70 to ‐80 mV. They were superimposed on a hyperpolarizing shift of the resting potential (h.s.) which gradually reached ‐60 mV in 50 min after insemination. 2. Unlike the hamster sperm, the cessation of flagellar motion of the first mouse sperm (‘1‐stop’) failed to induce the first h.r. but produced only a small hyperpolarizing ‘step’ of 3‐7 mV. Similar steps occurred for each of additional sperm with a one‐to‐one correspondence, 4‐50 sec ahead of the cessation of sperm motion. 3. In M × H eggs, the h.r. first appeared about 15 min after the ‘1‐stop’. The intervals of the h.r.s thereafter were in the range between 2‐10 min, in contrast to 30‐45 sec in hamster eggs inseminated with hamster sperm (H × H eggs). 4. The h.r.s in M × H eggs were abolished by intracellular injection of EGTA, suggesting that they were caused by periodic increase in the intracellular Ca 2+ concentration ([Ca 2+ ] i ) as in H × H eggs. 5. The gradual h.s. in M × H eggs was considered to be due mainly to an increase in Ca‐independent K permeability, since the resting potential beyond ‐60 mV at 50‐70 min after insemination was changed by only 3‐5 mV on the removal of Cl ions and on EGTA injection. 6. Histological observations revealed that the resumption of the second meiosis, the indication of egg activation, is delayed in M × H eggs by about 15 min, compared with that in H × H eggs. There was a good correlation between the delay of activation and that of the occurrence of the first h.r. 7. In M × H eggs, the probability of egg activation within 70 min was dependent on the number of sperm penetrations: 90% for more than ten sperm while 20‐30% for less than five sperm. Eggs in which sperm penetration was not followed by activation showed no h.r.s. 8. The mouse egg inseminated with mouse sperm showed small h.r.s (3‐4 mV) superimposed on the h.s. from ‐35 to ‐55 mV in 50 min after insemination. Both h.r.s and h.s. were associated with an increase in the membrane conductance. The h.s. was considered to be due mainly to a Ca‐independent increase in K permeability. 9. Iontophoretic injection of Ca 2+ into the unfertilized mouse egg could not increase the K conductance with injection currents up to 4 nA. However, the h.r.s were suggested to be resulted from a periodic increase in [Ca 2+ ] i , since they were abolished by injection of EGTA.