Regulation of internal Ca2+ by chilled bull and boar spermatozoa

Intracellular Ca2+ in ejaculated spermatozoa from five bulls and five boars was determined with indo-1,AM in Ca(2+)-free medium. Aliquots of each ejaculate were then wrapped and held either on ice or at 25 degrees C for 20 min. At this time all samples were returned to 25 degrees C, either Ca(2+)-free medium or medium containing 1 mM Ca2+ was added, and intracellular Ca2+ was determined for an additional 120 min. Before and immediately after chilling, internal Ca2+ in bull spermatozoa did not differ. However, exogenous Ca2+ caused both control and chilled bovine spermatozoa to accumulate Ca2+ over the subsequent 120 min (P < 0.01) with the control spermatozoal rate of Ca2+ intake being faster than that of the chilled (slopes, 29.531 vs 8.374 relative Ca2+ units/min; least squares means (lsmean) x 10(4) +/- 1.901 (pooled SE); P < 0.01). Viability of all spermatozoa was reduced after Ca2+ exposure, and the acrosomal morphology of chilled cells was adversely affected by Ca2+. For boar spermatozoa, chilling caused an immediate increase in internal Ca2+, confirming the greater sensitivity of boar spermatozoa to low temperatures. The presence of exogenous Ca2+ caused greater Ca2+ uptake by both control and chilled porcine cells relative to their Ca(2+)-free analogues (0.939 vs 0.764 and 1.015 vs 0.836 Ca2+ units; lsmean +/- 0.166 (pooled SE); P < 0.01 for control and chilled boar spermatozoa with and without Ca2+ at 150 min). Control spermatozoa, however, accumulated Ca2+ (P < 0.01) at a much greater rate (slope, 20.964 +/- 2.73 relative Ca2+ units x 10(4)/min; P < or = 0.001) than chilled cells, which only tended (P = 0.08) to accumulate Ca2+ (slope, 4.782 +/- 2.73 relative Ca2+ units x 10(4)/min). This study suggest that chilling causes a species-specific effect on Ca2+ regulatory capabilities of spermatozoa that differs from cold shock and that spermatozoa may be able to compensate, at least partially, for such injuries.