Respiration of steelhead trout sperm: sensitivity to pH and carbon dioxide

Abstract

Steelhead trout Oncorhynchus mykiss sperm held in seminal plasma or sperm‐immobilizing buffer (pH 8·6) at 10° C consumed O2 at the rate of c. 2 nmol O2 min−1 10−9 sperm; the rate of O2 consumption was not different in sperm held for 4 or 24 h. Decreasing the extracellular pH from 8·5 to 7·5 either by diluting semen with buffer titrated with HCl or by increasing the partial pressure of CO2 in the incubation atmosphere resulted in c. a 40% decrease in the rate of sperm respiration. The data did not, however, support the hypothesis that the precipitous reduction in the capacity for sperm motility that occurs as external pH is reduced is a result of a decrease in cellular metabolism. The rate of O2 consumption of freshly collected semen from different males was not correlated to cellular ATP content or to the proportion of sperm that were motile upon activation; the initial ATP content and sperm motility were positively correlated. The rate of O2 consumption was not significantly increased following sperm activation or by the addition of an uncoupler of oxidative phosphorylation, carbonyl cyanide p‐trifluoromethoxyphenylhydrazone, suggesting that these sperm have little, if any, capacity for increased oxidative metabolism.