Journal of Andrology
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Published-Ahead-of-Print August 1, 2007, DOI:10.2164/jandrol.107.003368

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Intracellular sodium increase induced by external calcium removal in human sperm

Víctor M Torres-Flores , Norma L García-Sánchez , and Marco T González-Martínez *

* To whom correspondence should be addressed. E-mail: tuliog{at}servidor.unam.mx.

In human sperm, removal of external calcium produces a fast Na+-dependent depolarization that is presumably due to sodium permeation through calcium channels. Calcium restoration produces a ouabain-sensitive hyperpolarization that brings the membrane potential to values frequently more negative than resting. In this work we show evidence indicating that external calcium removal induces an increase in the intracellular sodium ([Na+]i) and that this phenomenon is related to the Na+-dependent depolarization. Calcium restoration blocked the [Na+]i increase and then produced a slow decrease that was inhibited by ouabain. The [Na+]i increase was inhibited by nanomolar-micromolar calcium or by milimolar magnesium, which has been previously shown to inhibit the Na+-dependent depolarization. These evidence support the hypothesis that in zero-calcium medium a calcium channel, that would contribute to the resting intracellular calcium levels, allows sodium permeation producing depolarization and a significant [Na+]i increase. Sodium loading would stimulate the Na+,K+-ATPase, the activity of which contributes to the sperm hyperpolarization observed upon calcium restoration.


Key words: Sperm • sperm biology • sperm physiology






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