Abstract

Intracellular calcium, [Ca 2+](i), can regulate meiotic progression of mammalian oocytes. However, the role of [Ca 2+](i) in the regulation of the spermatogenic process and its cellular homeostatic mechanisms in spermatogenic cells has not been elucidated. Using intracellular fluorescent probes for Ca 2+ and immunodetection of plasma membrane (PM) Ca 2+-ATPases, we report that: a) rat round spermatids maintain [Ca 2+](i) levels of 60 ± 5 nM (SEM), as estimated with fluo-3 in single cells or fura-2 in cells in suspension; b) these cells regulate [Ca 2+](i), by actively extruding it using a PM Ca 2+-ATPase; c) rat spermatids also actively transport Ca 2+ by sarco-endoplasmic reticulum type ATPases (SERCA); d) rat spermatids possess non-mitochondrial intracellular Ca 2+(i) stores insensitive to thapsigargin but releasable by ionomycin; and e) rat spermatids do not activate Ca 2+ entry mechanisms by the release of Ca 2+ from SERCA-regulated stores. These results demonstrate that rat round spermatids can generate modulated intracellular Ca 2+ signals upon activation of Ca 2+ channels or Ca 2+ release from intracellular stores.