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Sperm motility in the horseshoe crab 4. extracellular ions and intra cellular ph are not mediators of motility initiation


, : Sperm motility in the horseshoe crab 4. extracellular ions and intra cellular ph are not mediators of motility initiation. Gamete Research 6(4): 327-342

Upon dilution into sea water, Limulus spermatozoa undergo a brief flurry of motility (duration < 60 s), after which they are nonmotile until encountering a sperm motility initiating peptide (SMI) that emanates from eggs. Utilizing highly purified SMI extracts and simplified seawater formulations (from which individual ions were deleted), no specific extracellular ion is required for either dilution-initiated or SMI-initiated motility. Deletion of 1 ion (Na+) produced dilution-initiated motility of very long duration (several hours). When motility is initiated by SMI (in normal seawater) there is an increase in intracellular pH (pHi), as indicated by the fluorescent probe, 9-amino acridine; this pHi change is not a trigger for motility. As a more general method examining ion movements, the fluorescent probe diS-C3-(5) was used to qualitatively measure changes in the membrane potential of spermatozoa. Although crude SMI extracts caused membrane depolarization, further purification resulted in an almost complete separation of this activity from SMI, showing that SMI activation is apparently an electroneutral event. (The membrane-depolarizing factor has a MW > 30,000 and does not initiate acrosome reactions.) Experiments utilizing the ionophore A23187 [calcimycin] and Ca+2-blocking agents (verapamil and TMB-8 [8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate]) provided tentative evidence that mobilization of intracellular Ca+2 may be required for motility initiation. Neither changes in pHi nor the influx of specific extracellular ions are direct mediators of SMI-initiated motility; experiments with pharmacologic agents indicate a possible role for intracellular Ca+2.

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