REACTIVATION OF EXTRACTED SPERM CELL MODELS 261 



lated from starfish sperm a relaxing substance by the Bendall (1954) 

 procedure for the extraction of Marsh factor from striated muscle 

 (Marsh, 1952). This component, in the presence of ATP and Mg+ + , 

 effects reactivation of invertebrate sperm models and also, interest- 

 ingly enough, brings about relaxation of shortened frog muscle (Kino- 

 shita, 1959). Similarly, extract of relaxing factor from frog muscle is 

 effective in the sperm reactivation system, and Kinoshita regards the 

 two factors functionally, if not chemically, identical (see Tibbs, this 

 symposium). 



Kinoshita's findings on invertebrate sperm are consistent with 

 our own view that something akin to "relaxing factor" is of general 

 significance in the operation of mammalian sperm models. If, for ex- 

 ample, Marsh-Bendall factor, extracted from the rabbit psoas muscle 

 (Bendall, 1953), is added to bull sperm models in the presence of ATP 

 and Mg++, no reactivation occurs (Bishop, 1958b). The addition of 

 Ca+ + , however, one effect of which is to block Marsh-Bendall factor 

 activity, results in immediate flagellation (Table II). Ca+ + alone has 

 no such inducing effect on the system. Treatment of relaxing factor 

 with Ca ++ prior to its addition to the models drastically reduces its 

 inhibitory activity (Bishop and Hoffmann-Berling, 1959). This Ca++- 

 dependent activity of muscle relaxing factor could not be mimicked 

 by nonspecific plasticizers such as EDTA or inorganic pyrophosphate 

 in mammalian sperm models (cf. Nelson,. 1959). Whether mammalian 

 spermatozoa contain a relaxation substance identical with that re- 

 ported in invertebrate sperm by Kinoshita is not known, but they do 

 appear to possess some component which binds Ca++ readily and has 



Table II. Responses of bull sperm models to Marsh-Bendall factor 

 extracted from rabbit skeletal muscle" 



Additions to Extracted Sperm Responses 



ATP 10-W + 



Ca++ \0r*M 



ATP 10" 3 M + Ca++ 10-W + 



ATP \0~ 3 M + MBF - Ca++ - 



+ Ga++ \0-*M + 



ATP 10- 3 A/ + MBF - Ca++ 



+ Mg++ 5 X 10" 3 A/ 



« Data from Bishop, 1958b; Bishop and Hoffmann-Berling, 1959. 



