ELECTROPHYSIOLOGICAL AND MORPHOLOGICAL STUDIES OF RANA OOCYTES DURING MEIOTIC MATURATION (ATPASE, CONDUCTANCE, MEIOSIS, SODIUM, POTASSIUM)

Abstract

In amphibia, pituitary gonadotropins induce the somatic cell portion of the prophase-arrested follicle to synthesize and release progesterone, which, in turn, reinitiates the meiotic divisions of the oocyte. The oocyte then completes one and one-half meiotic divisions, during which its large nucleus swells and breaks down. The meiotic divisions arrest again, this time at second meiotic metaphase. Fertilization allows completion of the meiotic divisions and is followed by the cleavage phase of development.;In the present thesis, I have used scanning electron microscopy, transmission electron microscopy, cytoplasmic transfer, tracer-flux techniques, intracellular recording, and current-/voltage-clamp techniques to study the electrophysiological and morphological characteristics of prophase-arrested and maturing follicular oocytes and of oocytes denuded of investing somatic cells. The morphology of Rana oocytes was found to be very similar to that of other amphibian oocytes, but differences were found between follicular and denuded oocytes. A pituitary-extract induced hyperpolarization was found to be: (1) subserved by an increase in follicle K('+) conductance, (2) dependent on the presence of follicle cells, (3) inhibited by some treatments which are known to decrease the conductance of gap junctions. Studies on denuded oocytes showed that: (1) a portion of the resting potential of prophase-arrested oocytes was due to an electrogenic Na('+), K('+) pump. This electrogenic component was no longer detectable after nuclear breakdown. (2) Preventing progesterone-induced depolarization by means of a voltage-clamp did not prevent nuclear breakdown. (3) Changes in conductance and capacitance occur in Rana oocytes during maturation (4) Some oocytes exhibited action potentials after nuclear breakdown. (5) Cytoplasmic factors from maturing oocytes were able to induce nuclear breakdown and depolarization when injected into naive oocytes, but treatment of recipient oocytes with cycloheximide prevented subsequent depolarization. These findings indicate that during meiotic maturation, major changes occur in the oolemma, some of which depend on protein synthesis, and some of which may depend on internalization of specific membrane domains. These changes may be prerequisite to the development of competency for proper fertilization.