(A) Nominally Ca2+-free medium attenuates HCO3−-induced cAMP synthesis by SACY in wild-type and bPAC sperm. Inhibition of phosphodiesterases by IBMX in wild-type sperm and light stimulation in bPAC sperm increases cAMP levels without extracellular Ca2+. Data are plotted as mean ± s.d.; (n) = number of experiments; p values calculated using Student's t test. (B) In the absence of extracellular Ca2+, HCO3−-induced tyrosine phosphorylation (pY) is strongly attenuated. In bPAC sperm, light stimulation is sufficient to restore tyrosine phosphorylation. (C) Light stimulation restores flagellar beating of Slc9a10-null/bPAC sperm. Flagellar waveform of Slc9a10-null/bPAC sperm before (left) and after light stimulation (right). Successive, aligned, and superimposed images creating a ‘stop-motion’ image, illustrating one flagellar beating cycle. Scale bar: 30 µm. (D) Upon light stimulation, Slc9a10-null/bPAC sperm fertilize oocytes in vitro (mean ± s.d.; (n) = total number of oocytes from three independent experiments).