Carbon dioxide and pH affect sperm motility of white sturgeon (Acipenser transmontanus)

Abstract

Maintenance of sperm at pH values less than approximately 7.5 inhibited the onset of motility when sperm were subsequently diluted with water; maintenance at pH values above approximately 8.2 was associated with maximal motility upon dilution with water. Within 5-min of exposure to low pH buffer (pH 6.9), there was a 50% decline in sperm motility upon dilution with water suggesting that exposure to low pH interferes with motility within a time frame that may affect fertilization. In most instances, maintenance of sperm under CO2 at a pressure of 4-5 kPa almost completely blocked their capacity for motility. Furthermore, exposing semen to increasing partial pressures of CO2 up to about 1 kPa resulted in a marked decrease in semen pH. These observations are consistent with the findings that the buffering capacity of semen is particularly low at physiological pH, and that this low buffering capacity corresponds to the highest pH sensitivity of the capacity for sperm motility. The low seminal buffering capacity may represent a physiological adaptation in the control of sperm function. It may also represent a vulnerability to environmental hypercapnia or metabolic acidosis.