Analysis of calmodulin acceptor proteins and the influence of calmodulin antagonists on human spermatozoa

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Abstract
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.