Animal Reproduction Science 91 (2006) 123–132 Ultrastructural localisation of calcium deposits in pig ovarian follicles J. Rozinek a , R. Rajmon a,∗ , J. Petr b , J. Rohl´ ık a , M. Jeˇ seta a , M. Sedm´ ıkov´ a a , D. ˇ Reh´ ak b , F. J´ ılek a a Department of Veterinary Science, Czech University of Agriculture in Prague, Prague 6, Suchdol 165 21, Czech Republic b Research Institute of Animal Production, Prague 10, Uhˇ r´ ınˇ eves, Czech Republic Received 3 September 2004; received in revised form 3 March 2005; accepted 29 March 2005 Available online 28 April 2005 Abstract Calcium intracellular signaling regulates many intracellular events including oocyte maturation. This signaling is strongly dependent on the influx of calcium ions from extracellular spaces and on the state of intracellular calcium stores. In this study, intracellular calcium deposits were detected in follicle-enclosed pig oocytes using the combined oxalate–pyroantimonate method. These deposits were observed in the nucleus, the mitochondria, the cytoplasm, and on the surface of lipid droplets. The amount of calcium deposits was expressed as a percentage of the area of the respective cellular compartment, which is covered with calcium deposits on ultrathin sections. The distribution of calcium deposits in oocytes changed during folliculogenesis. The amount of calcium deposits in nuclei (1.11% of the area of oocyte nuclei) and cytoplasm (1.02%) in oocytes from secondary and early antral follicles (0.90% nuclei; 0.99% cytoplasm) is significantly lower (P < 0.05) than the amount of calcium deposits in these compartments in oocytes from primary follicles (2.51% nuclei; 2.34% cytoplasm) or antral follicles with growing oocyte (2.91% nuclei; 2.21% cytoplasm). The amount of calcium deposits in mitochondria of oocytes from primary follicles (1.27%) or antral follicles with growing oocyte (1.14%) is significantly lower (P < 0.05) than in the nucleus (2.51% in oocytes from primary follicles; 2.91% in growing oocytes from antral follicles) or cytoplasm (2.34% in oocytes from primary follicles; 2.21% in growing oocytes from antral follicles). The amount of calcium deposits in the cytoplasm of fully-grown oocytes (1.46%) dropped to levels significantly lower (P < 0.05) than those observed in the oocyte nucleus (2.29%). On the basis of these data, we can conclude that the population of ∗ Corresponding author. Tel.: +420 224392935; fax: +420 23438141. E-mail address: rajmon@af.czu.cz (R. Rajmon). 0378-4320/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2005.03.010