Analysis of calmodulin acceptor proteins and the influence of calmodulin antagonists on human spermatozoa.
The possible role of calmodulin in regulating a number of calcium-dependent functions exhibited by human spermatozoa was investigated by using the antagonists trifluoperazine and calmidazolium. At high doses both antagonists inhibited the motility of human spermatozoa and induced a concomitant rise in [Ca2+]i and a decline in cAMP. Lower doses of these antagonists, particularly calmidazolium, suppressed the ability of human spermatozoa to generate reactive oxygen species and exhibit sperm-oocyte fusion, without influencing [Ca2+]i, cAMP, or motility. This inhibition of sperm-oocyte fusion was effective even if the spermatozoa were subsequently exposed to A23187, suggesting that calmodulin may regulate this aspect of human sperm function at a point downstream from calcium influx. Both radiolabelling and affinity chromatography techniques were used to detect a number of calcium-dependent and calcium-independent calmodulin acceptor proteins in the human spermatozoon. The major calcium-dependent acceptor proteins exhibited Mr values of 32,000 and 22,000-27,000, respectively, and did not appear to be associated with the sperm plasma membrane.
Aitken
R J
RJ
MRC Unit of Reproductive Biology, Edinburgh, Scotland.
Clarkson
J S
JS
Hulme
M J
MJ
Henderson
C J
CJ
D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000502:physiology*; D002148:Calmodulin-Binding Proteins / Q000502:physiology*; D000242:Cyclic AMP / Q000032:analysis; D006801:Humans; D007093:Imidazoles / Q000037:antagonists & inhibitors; D008297:Male; D013084:Sperm-Ovum Interactions / Q000187:drug effects; D014268:Trifluoperazine / Q000037:antagonists & inhibitors
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D007093:Imidazoles; D014268:Trifluoperazine; C031938:calmidazolium; D000242:Cyclic AMP; D002118:Calcium