The BSA -induced [Ca2+]
rises start in sperm tail and propagate toward the head. (A) Representative time courses of the [Ca2+]i changes in the principal piece (PP1), midpiece (MP1) and head of the sperm. Increases in [Ca2+]i start in the principal piece and propagate to the head. The Ca2+ ionophore ionomycin (5 μM) induced [Ca2+]i increases simultaneously in all subregions. (B-C) Time differences between the application of BSA (B, 1 mg/ml; C, 5 mg/ml) and the onset of fluorescence changes (defined as the time point when ΔF/F0 started to have steep rise) in different regions within the principal piece (PP1, PP2), midpiece (MP1, MP2) and head as shown in the inset. PP1 and MP1 are both 5 μm from the annulus. There is a 5 μm distance from PP1 to PP2, and from MP1 to MP2. * indicates statistically significant (P < 0.05).