ULTRASTRUCTURAL-LOCALIZATION OF INTRACELLULAR CALCIUM STORES IN XENOPUS OVARIAN FOLLICLES AS REVEALED BY CYTOCHEMISTRY AND X-RAY-MICROANALYSIS

The ultrastructural localization of calcium in full-grown ovarian foll icles of Xenopus laevis was demonstrated after fixation in the presenc e of fluoride ions and by means of energy dispersive X-ray microanalys is. In hormonally untreated follicles (prophase I-arrested oocytes), t wo calcium sites were detected: follicle cells and oocyte pigment gran ules. In follicle cells, calcium containing deposits were preferential ly associated with macrovilli, which ended by gap junctions. In human chorionic gonadotropin treated follicles (meiotically reinitiated oocy tes), deposits were only seen in follicle cells. This is the first rep ort of the cytochemical detection of intracellular Ca2+ in follicle ce lls of amphibians. The possible involvements of these Ca2+ stores in m ediating the hormonal control of meiotic maturation are discussed.