RESUMO
Caltrin (calcium transport inhibitor) is a family of small and basic proteins of the mammalian seminal plasma which bind to sperm cells during ejaculation and inhibit the extracellular Ca2+ uptake, preventing the premature acrosomal exocytosis and hyperactivation when sperm cells ascend through the female reproductive tract. The binding of caltrin proteins to specific areas of the sperm surface suggests the existence of caltrin receptors, or precise protein-phospholipid arrangements in the sperm membrane, distributed in the regions where Ca2+ influx may take place. However, the molecular mechanisms of recognition and interaction between caltrin and spermatozoa have not been elucidated. Therefore, the aim of this article is to describe in depth the known structural features and functional properties of caltrin proteins, to find out how they may possibly interact with the sperm membranes to control the intracellular signaling that trigger physiological events required for fertilization.
RESUMO
The permeability barrier of the urothelium (covering the mammalian urinary tract) has stimulated interest in the role of the luminal membrane in the barrier function. To know how membrane lipids may affect the permeability barrier we prepare endocytic vesicles of different lipid composition entrapping a fluorescent dye (HPTS) and its quencher (DPX) using a dietary strategy (rats fed with commercial, oleic acid- or linoleic acid-enriched diets) followed by endocytosis induction. Vesicular leakage was measured by a fluorescence requenching technique. The results showed (1) endocytosed vesicles can release their content; (2) a linoleic acid-rich diet did not change either the mechanism of leakage or the amount of released material relative to the control; and (3) a oleic acid-rich diet greatly affected the mechanism of release. Thus, the dietary fatty acids can modify the urothelial cell physiology altering the pathway of endocytosed urinary fluid.
