258 



DAVID W. BISHOP 



T.O 



7-.4 



PH 



Fig. 4. Effect of pH on beat frequency of models of sperm of sea urchin 

 (O) and starfish (©), reactivated with 1 mM ATP, 5 mM Mg++ and 10 

 mM histidine. (After Kinoshita, 1958.) 



to 7.8 causes no significant change in flagellar rate, as determined 

 visually by ordinary microscopic methods (Kinoshita, 1958). 



In studies of cationic requirements, Mg++ proves essential for re- 

 activation of sperm models of both invertebrate and vertebrate species 

 (Hoffmann-Berling, 1955a; Kinoshita, 1958; Bishop and Hoffmann- 

 Berling, 1959); Ca+ + , on the other hand, while not required in the 

 bathing medium, facilitates reactivation at least of mammalian sperm, 

 possibly by virtue of an effect on plasticity or "relaxation" of the 

 cells (see below). It is to be noted that divalent cations, particularly 

 Mg+ + , are probably bound and are not entirely removed by extrac- 

 tion; thus, absolute requirements are difficult to quantitate. Kinoshita 

 (1958) demonstrated an optimal exogenous Mg++ concentration of 

 10 mM for models of sea urchin and starfish sperm (Fig. 5). These cells 

 were reactivated by ATP in the presence of histidine, which has a 

 chelating action, and the concentrations as indicated should be re- 

 garded with this in mind. In bull sperm models the concentrations 

 of Mg++ in both extraction and reactivation media influence the 

 time required for reinitiation of motility by ATP (Table I). 



K+ and Na+ are completely interchangeable in this system, and 



