Expression of capacitation-dependent changes in chlortetracycline fluorescence patterns in mouse spermatozoa requires a suitable glycolysable substrate

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Abstract
Chlortetracycline (CTC) fluorescence patterns were assessed in epididymal mouse sperm suspensions capacitated in exogenous substrate-containing and substrate-free media. A capacitation-dependent transition from a majority of acrosome-intact cells expressing the uncapacitated F pattern of fluorescence to a majority with the capacitated acrosome-intact B and acrosome-reacted AR patterns was confirmed for suspensions incubated a total of 120 min in the presence of a glycolysable substrate, glucose. In contrast, assessment of spermatozoa incubated for 120 min in substrate-free medium revealed a majority of cells with the uncapacitated F pattern, despite an earlier demonstration that such cells are essentially capacitated: upon the introduction of glucose, suspensions are immediately highly fertile. When a suitable glycolysable substrate, either glucose or mannose but not fructose, was added to such suspensions, the distribution of CTC patterns changed within 10 min to a majority of B and AR patterns. Furthermore, the degree of change from uncapacitated to capacitated patterns was substrate concentration-dependent. In contrast, the introduction of the non-metabolizable substrates 2-deoxyglucose and 3-O-methylglucose and the oxidizable substrates sodium pyruvate and sodium lactate caused no change in the patterns from those seen in substrate-free medium. The in-vitro fertilizing ability of sperm suspensions to which increasing amounts of glucose or mannose were added, after initial substrate-free preincubation, directly paralleled the changes in CTC patterns and was as rapid as for suspensions incubated continuously in either hexose. We therefore conclude that the alteration in position of surface component to which CTC binds is not only capacitation-dependent, but also energy-dependent. In the absence of an appropriate exogenous glycolysable substrate, the final transition cannot occur, even though the cells are essentially capacitated.