No abstract

SUMMARYMeasurements of membrane potential and resistance have been made in zona-free eggs of mice and hamsters. The mean + S.D. values for membrane potential were -91 + 28 mV (mouse) and -97 + 29 mV (hamster) and for input resistance were 430 + 230 MQl (mouse) and 410 + 150 MQ (hamster) respectively. Large fluctuations (20 mV) of membrane potential occurred apparently at random and these were accompanied by changes of membrane resistance. Depolarizing current pulses passed through the recording micro-electrode evoked action potentials in eggs of both species. The threshold for excitation was about -50 mV, the maximum rate of rise of the action potential was about 3 V . s-I and its peak value was about + 13 mV. Action potentials could be evoked in eggs bathed in sodium-free solution or in normal solution containing tetrodotoxin (3/M). The presence of cobalt (5-20 mM), lanthanum (1 mM) or verapamil (200-400 uM) in the bathing solution suppressed the action potential. Raising the extracellular calcium concentration from 4 to 40 mm increased the peak value of the action potential by 25 mV. It is concluded that the plasma membranes of mouse and hamster eggs have voltage-dependent calcium channels.

SUMMARYMeasurements of membrane potential and resistance have been made in zona-free hamster eggs. The resting potential lay in the range -9 to -100 mV and the input resistance fell in the range 14 to 440 MQ; high resting potentials were associated with large input resistances. Calcium injected ionophoretically into an egg from an intracellular micro-electrode caused a reduction of the membrane resistance. The estimated reversal potential for the calcium-evoked response was about -80 mV and its amplitude depended on the extracellular concentration ofpotassium but not on the chloride concentration. We conclude that membrane potassium channels open in response to a rise in the cytosolic concentration of calcium ions. Evidence is presented to suggest that micro-electrode recordings of the membrane potential and resistance of eggs suffer from an impalement leak artifact. The presence of the artifact lowers the resting potential and resistance of the cell so that intracellular calcium injection causes a hyperpolarization. We conclude that a hyperpolarizing response to calcium would be unlikely in the absence of an impalement artifact.

Follicular growth in the normal oestrous cycle of the guinea-pig is biphasic. The first wave of follicular growth culminates on Days 10--11 while the second wave ends in ovulation.

1. The presence of two glass beads (7 × 3 mm) in each horn of the uterus was associated with a reduction of 3‐4 days in the length of the oestrous cycle. 2. Two beads inserted into each uterine horn between days 2 and 4 exerted a greater effect on the oestrous cycle than either one bead in each horn or four beads in one horn only. Two beads located in one horn failed to affect cycle length. 3. Measurement of the volume of the corpora lutea showed that distension of the uterus induced a premature regression in the size of the luteal bodies. 4. When glass beads were present in one uterine horn, early and unilateral regression of the corpora lutea in the ovary adjacent to the distended horn was observed. Regression of the corpora lutea in the opposite ovary proceeded normally. 5. In view of the local effect of uterine distension and other information, it is concluded that each uterine horn can produce a luteolytic substance which is conveyed to the neighbouring ovary to act upon the corpora lutea.