Physiology of fertilization of mammalian eggs

Abstract

Cell attached patch recordings have been made from zona-free mouse eggs. Potassium channels which show anomalous and delayed rectification have been observed. The conductance of these channels was as high as 160pS. They have been shown to open and shut independently of one another. Another channel with a conductance of about 50pS has been noted and is believed to be a chloride channel. Calcium channels with mean current amplitudes of 1.10 + 0.33pA (mean + SD, n=35) and a conductance in the range 7.5 to 20pS, have also been recorded.

Before insemination the membrane potential of zona-free hamster eggs, measured with intracellular electrodes lay in the range -8 to -47mV (whilst bathed in a modified Krebs Ringer solution - called "normal"). In five eggs impaled during this study, the membrane potential was more negative than -61mV. In these eggs calcium action potentials could be evoked by depolarizing pulses. It is suggested that eggs which do not show such action potentials suffer from impalement leaks or have possibly undergone "in vitro deterioration".

Inward channel currents have been observed in synchrony with the rising phase of the action potential.

Preliminary data are presented on whole cell recording experiments.

In zona-free hamster eggs current clamped at potentials more negative than about -80mV, sperm egg fusion was associated with a depolarization, which in some cases elicited an action potential. Such depolarizations or sperm evoked action potentials were also observed in eggs bathed in a solution resembling oviducal fluid, with a potassium concentration of 25mM or in a solution with a sodium concentration of ImM. Such depolarizations were followed by transient recurring depolarizations.

During fertilization of eggs with low membrane potentials, no response was observed at the time of sperm fusion, but transient recurring hyperpolarizations were later recorded (as seen by other workers).

Similar results were obtained during fertilizations in calcium free solutions containing substituted magnesium and strontium.

"Action currents" have been measured, during fertilization with cell attached patch pipettes. Results of these experiments reveal the presence of (i) spikes superimposed on the repolarizing phase of transient recurring hyperpolarizations, (ii) the latter are sometimes followed by after depolarizations and (iii) these responses were superimposed on a depolarizing shift.

Trinitrotoluene is a nitro explosive belonging to the Benzene Group and is hence a coal tar product, and therefore similar in origin to Aniline, the basis of Aniline Dyes.

Toluene is Methyl Benzene C₆H₅(CH)3₆₂₃₄₅₆ and T.N.T. is obtained by nitrating this substance by a mixture of nitric and sulphuric acids.

Toluene (sometimes incorrectly called Toluol) is a colourless liquid and is obtained by the fractional distillation of coal tar - a by- product in the manufacture of coal gas.

It is lighter than water, having a sp.gr. of .8824 and it boils at 1100 C.