THE EFFECTS OF HEAVY METAL IONS ON THE MOTILITY OF SEA URCHIN SPERMATOZOA

¹ Department of Physiology, Emory University, Atlanta, Georgia 30322; Department of Physiology, Medical College of Ohio, Toledo, Ohio 43614; and Marine Biological Laboratory, Woods Hole, Massachusetts 02543

Optimum motility of sea urchin spermatozoa for a period adequate to initiate the process of fertilization requires an apparently critical level of certain heavy metal ions. Increase of some of the divalent cations above the "normal" seawater content accelerates or depresses the swimming speed in dose- or time-dependent fashion (or both). The different patterns of Arbacia sperm swimming speed response to the individual cation supplements (Cu, Zn, Mn, Hg) may reflect differences in rate of penetration into the cell, binding of atcive groups or selective inhibition of as yet unspecified enzymes at or below the cell surface which directly or indirectly contribute to regulation of flagellar contractility. The concentrations tested ranged from 500 nM up to 10 mM. The "optimum" concentrations fell between 1 to 10 micromolar Cu, Zn and Hg on initial exposure, while Mn was moderately inhibitory at these levels. EDTA, up to 10^-4 molar, exerts no adverse effect on sperm propulsion, while 8 x 10^-4 M almost completely blocks the motility. Within this short concentration span, the EDTA appears not only to bind essential seawater cations, but may also deplete those intracellular regulatory cations which otherwise may exist in a state of dynamic equilibrium with the seawater.