Stimulation of Ca2+ uptake into epididymal bull spermatozoa by analogues of amiloride


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Certain amiloride analogues 3′,4′‐dichlorobenzamil 2′,4′‐dimethylbenzamil and α′,2′‐benzobenzamil hydrochloride (ATBB) stimulate calcium accumulation and motility by epididymal bovine spermatozoa. This stimulation can be seen at a range of 0.1–0.4 mM, while at higher concentration there is inhibition of calcium uptake by these amiloride analogues. The amiloride derivative 5‐(4‐chlorobenzyl)‐2′,4′‐dimethylbenzamil (CBDMB), which bears a 4‐chlorobenzyl substituent on the 5‐amino nitrogen atom, did not stimulate calcium uptake. The amiloride analogue 3′,4′‐dichlorobenzamil inhibits the Na+/Ca2+ ‐exchange activity in isolated plasma membrane vesicles, and the stimulatory effect of 3′,4′‐dichlorobenzamil on calcium uptake into epididymal sperm could be seen in Na+ ‐free medium. Thus, the stimulation of Ca2+ accumulation in the cells caused by 3′,4′‐dichlorobenzamil is not a result of inhibiting the Na‐dependent Ca2‐ clearance. There is no stimulation of Ca2+ uptake into ejaculated cells by adding 3′,4′‐dichlorobenzamil, which is not due to the presence of the calcium‐transport inhibitor (caltrin) in these cells [Rufo, G. A., Schoff, P. K. & Lardy, H. A. (1984) J. Biol. Chem. 259, 2547–2552]. The stimulatory effect of 3′,4′‐dichlorobenzamil on Ca2+ uptake is inhibited by the voltage‐dependent Ca2+‐channel blockers nifedipin and diltiazem. This indicates that the stimulation of Ca2+ uptake by the amiloride analogues is due to the activation of a voltage‐dependent Ca2+ channel of the plasma membrane.

Original languageEnglish
Pages (from-to)529-535
Number of pages7
JournalEuropean Journal of Biochemistry
Issue number2
StatePublished - 11 Sep 1990


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