Spermine exposure (purple) but not acidic pH (brown) significantly shifted I Cs + midpoint activation upon heat. However, the spermine-induced shift resulted in V 1/2 change from - 3.7 mV to only - 25.3 mV, which is still outside of the physiological range of membrane voltages for non-capacitated spermatozoa, as shown by the dotted and shaded area. The shift of V 1/2 upon heat for nonexposed control spermatozoa recorded with normal (pH = 7.4) pH (black) is shown for comparison. Data are presented as mean values ± S.E.M., n corresponds to the number of cells used. Data are cumulative from Figs. 1 g, 3 d, and 4f . P- values were as follows: 0.001 (spermine; magenta) and 0.0013 (control; black).
