Intracellular Ca2+ homeostasis in rat round spermatids

Abstract

Intracellular calcium, [Caz+], can regulate meiotic progression of mammalian oocytes. However, the role of [Ca2+], in the regulation of the spermatogenic process and its cellular homeostatic mechanisms in spermatogenic cells has not been elucidated. Using intracellular fluorescent probes for Ca2f and immunodetection of plasma membrane (PM) Ca2+-ATPases, we report that: a) rat round spermatids maintain [Ca*+]i levels of 60 k 5 nM (SEM), as estimated with flu03 in single cells or fura- in cells in suspension; b) these cells regulate [Ca2+], by actively extruding it using a PM Ca2+- ATPase; c) rat spermatids also actively transport Ca *+ by sarco-endoplasmic reticulum type ATPases (SERCA); d) rat spermatids possess non-mitochondrial intracellular Ca2+, stores insensitive to thapsigargin but releasable by ionomycin; and e) rat spermatids do not activate Ca2+ entry mechanisms by the release of Ca *+ from SERCA-regulated stores. These results demonstrate that rat round spermatids can generate modulated intracellular Ca2+ signals upon activation of Ca2+ channels or Ca2+ release from intracellular stores.