Abstract
The calcium-transport inhibitor, caltrin, isolated from bovine seminal fluid inhibits calcium accumulation by bovine epididymal spermatozoa, spermatozoal mitochondria, rat liver mitochondria and beef heart mitochondria. Respiration studies demonstrate a marked stimulation of oxygen consumption by caltrin in filipin-treated spermatozoa and rat liver mitochondria. A biphasic effect of caltrin on rat liver mitochondrial respiration was noted, with stimulation at low caltrin concentrations and inhibition as the concentration of caltrin is increased. The ability of caltrin to uncouple and/or inhibit respiration in filipin-treated spermatozoa and isolated liver mitochondria indicates that inhibition of mitochondrial calcium accumulation by caltrin results from one of these mechanisms. Only a marginal effect of caltrin on respiration of intact spermatozoa was observed; indicating that the plasma membrane is impermeable to this protein. The differential effect of caltrin on respiration of intact and permeabilized spermatozoa indicates that caltrin inhibition of Ca 2+ uptake into spermatozoa in vivo occurs at the level of the plasma membrane.
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