Inhibition of human sperm motility by inhibitors of choline acetyltransferase.

Human spermatozoa contain choline acetyltransferase (ChA), acetylcholinesterase and acetylcholine (ACh). There is no storage pool for ACh in spermatozoa. Therefore, ChA inhibitors should exhibit dramatic effects in the alteration of levels and turnover of ACh and sperm motility. The effects of two groups of ChA inhibitors, 2-benzoylethyltrimethylammonium (BETA) and related compounds and halogenoacetylcholines (cholinesters of iodo-, bromo- and chloroacetic acids; XACh, where X = l, Br or Cl), on the motility index of human ejaculated sperm were studied. These investigations gave the following results: 1) BETA was a potent inhibitor of ChA from monkey brain (I50, 4.8 x 10(-6) M), homogenates of rat spermatozoa (I50, 6.5 x 10(-5) M) and homogenates of human spermatozoa (I50, 5.6 x 10(-5) M). It decreased the motility index of human spermatozoa (I50, 8.5 x 10(-8) M) at concentrations higher than 10(-8) M after a contact time of 5 to 60 min. It decreased the motility index of human spermatozoa by about 80% after 5 min and by 95% after 1 hr at a concentration of 10(-6) M. 2) There was a positive relationship between the inhibition of ChA and the depression of the motility index of human spermatozoa among these inhibitors. Both the number of motile cells and the graded motility were decreased. 3) All ChA inhibitors studied are quaternary ammonium compounds that do not significantly cross membrane barriers. 4) Both human sperm cells and human sperm cell homogenates had the same ChA activity. 5) Seventy-five percent of ChA activity could be washed away from human spermatozoa. 6) The same amount of ChA inhibition was observed when BETA was added to the homogenate of sperm cells or whole sperm cells. All of these observations indicate that sperm cell ChA is accessible to BETA and related quaternary ammonium compounds. These studies indicate that ACh is possibly synthesized by the tail and is a local hormone in the coordination of contraction and relaxation cycles of spermatozoan flagella.