As in rats and humans, we have shown the presence of the high-affinity glucose transporter GLUT3 in mouse sperm, indicating the immense need of sperm for glucose. Interestingly, the presence of cytochalasin B but not phloretin inhibited the PPP activity, although both are able to bind to facilitative glucose transporters (GLUT1, GLUT3) and to inhibit glucose uptake by sperm in different species. Cytochalasin B has been shown to bind to GLUT3 in human testis, to inhibit glucose transport, and to decrease the glycolytic rate in human sperm. Cheap Diskus Advair
The differential response of the PPP to cytochalasin B and phloretin was surprising since we expected that metabolism through both glycolysis and the PPP would be decreased after glucose uptake inhibition. Although the lack of inhibition of the PPP in the presence of phloretin has not been explained, it may be supposed that the cellular effect of phloretin was not limited to glucose uptake inhibition. For example, phloretin has been shown to enhance chick myoblast fusion by activating a calcium-dependent potassium channel. In our study, phloretin may activate the PPP by an unknown mechanism, leading to an increased generation of 14CO2 from small quantities of [1-14C]glucose entering the gametes despite transport inhibition.