Figure 6. Molecular mechanisms involved in the sperm chemotaxis mediated by progesterone.

1, P-P_R interaction; 2, tmAC activation and cAMP synthesis; 3, PKA activation; 4, protein phosphorylation; 5, stored Ca²⁺ released through IP₃R channel; 6, first Ca²⁺ influx through SOC channel; 7, activation of sGC with an intracellular cGMP increase; 8, PKG activation and a second Ca²⁺ influx probably through other calcium channels; 9, change in sperm swimming direction. Data from this study are shown with black arrows while unknown connecting steps are marked with red arrows. See text for further explanation of the model.