Mechanical immobilization of rat sperm does not change their oxygen consumption rate

Rat sperm are mechanically immobilized by the mucin immobilin during storage in the cauda epididymidis. We thought this mechanical immobilization might lower the respiration rate of caudal sperm since it is well established that both the respiration rate and adenosine triphosphate (ATP) dephosphorylation rate of certain invertebrate sperm are markedly reduced when they are mechanically immobilized. To measure the oxygen consumption rates of rat sperm, we used a conventional polarographic oxygen sensor. However, we used an unstirred sample chamber since we found that sperm are unusually fragile and are quickly killed by even moderate stirring. When caudal sperm were diluted in physiological salt solutions, they became vigorously motile and consumed oxygen at a rate of approximately 20 microliter O2/10(8) sperm/hour at 34.5 degrees C for dilutions between 20- and 200-fold. In confirmation of the work of Brokaw et al., we found that when the motility of sea urchin sperm was reduced progressively with increasing amounts of methylcellulose, the sperm consumed oxygen at a markedly reduced rate. In contrast, we found that when caudal rat sperm were mechanically immobilized, either by methylcellulose or by immobilin, their oxygen consumption rate did not differ detectably from that of vigorously motile sperm. Thus, the coupling of metabolism to motility differs significantly between these two types of sperm. We conclude that immobilin does not change the respiration rate of caudal rat sperm.