Role of quinine-sensitive ion channels in volume regulation in boar and bull spermatozoa

The ability to reverse swelling caused by hypo-osmotic stress is an importa nt cell function; in spermatozoa, it is likely to be of consequence during ejaculation and also during the thawing process that terminates cryopreserv ation. In this study, the time course of boar and bull sperm volume changes after exposure to hypoosmotic conditions at 39 degreesC was recorded. Cell volume measurements of washed sperm suspensions were performed electronica lly in Hepes-buffered saline solutions of 300 and 180 mosmol kg(-1) contain ing 2.5 mmol K+ l(-1). Treatment with quinine in the presence or absence of the potassium ionophore valinomycin was used to determine whether potassiu m channels were involved in the reversal of swelling. After exposure to hyp o-osmotic conditions, both bull and boar spermatozoa showed initial swellin g (up to 200% and 140% of initial volume, respectively, within 5 min), whic h was subsequently partially reversed (to about 150% and 120%, respectively , after 20 min). Incubation with quinine led to an increase in swelling in both species. However, bull sperm volume was already maximal (up to 294%) a fter 30 s and declined thereafter, whereas boar sperm volume increased slow ly to a maximum of about 220% after 20 min. Valinomycin treatment caused qu inine-induced swelling in bull spermatozoa to decrease rapidly to control ( no quinine, no valinomycin) values, whereas in quinine-treated boar spermat ozoa it had an opposite, enhancing effect. Interpreting these results in th e light of data from studies by others on a variety of cell types, it is pr oposed that swelling-activated potassium channels are involved in regulator y volume decrease in both species of spermatozoa, but that boar spermatozoa may contain fewer swelling-activated chloride channels than do bull sperma tozoa.