Stimulation of Ca2+ uptake into epididymal bull spermatozoa by analogues of amiloride.
Certain amiloride analogues 3',4'-dichlorobenzamil 2',4'-dimethylbenzamil and alpha',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.
Breitbart
H
H
Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
Cragoe
E J
EJ
Lardy
H A
HA
D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D004110:Diltiazem / Q000494:pharmacology; D004822:Epididymis; D005372:Filipin / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism*; D013329:Structure-Activity Relationship
C041470:3',4'-dichlorobenzamil; C066056:alpha',2'-benzobenzamil; C053494:2',4'-dimethylbenzamil; D000584:Amiloride; D005372:Filipin; D012964:Sodium; D004110:Diltiazem; D009543:Nifedipine; D002118:Calcium