title: Potassium movement during sodium-induced motility initiation in the rat caudal epididymal spermatozoa.
abstract: The sodium-induced sperm motility initiation of the rat cauda epididymal sperm has been studied in different potassium concentrations. High K+ inhibited motility initiation. At a K+ concentration of 50 mM (concentration found in the rat cauda epididymidis), sperm motility was inhibited by 80%. K+ movement across the sperm membrane has been followed by using 86Rb+ as a marker for K+. When the 86Rb+ preloaded sperm were suspended in a sodium-free medium, there was a little efflux of 86Rb+. However, if they were suspended in a sodium-containing medium, the efflux rate was greatly increased. This increase in 86Rb+ efflux rate was associated with an initiation of sperm motility. Both 86Rb+ efflux and motility initiation were triggered by a K+ ionophore 18-crown-6 (2 X 10(-3)M). However, the ionophore-induced 86Rb+ efflux and motility initiation only occurred in the presence of extracellular Na+. Tetraethylammonium (TEA) chloride, which blocks K+ channels, inhibited motility initiation in a dose-dependent manner. Changes in the membrane potential of sperm have been followed using the fluorescent dye diO-C6-(3) whose fluorescence in sperm suspension changes markedly with changes in sperm membrane potential. During motility initiation, there was a fall in fluorescence of the dye due to increased partition into sperm cells. This observation may indicate a hyperpolarization of the sperm membrane during motility initiation. It was concluded that sperm motility initiation is associated with a complex ionic event. Na+ enters sperm cells in exchange with H+ and K+. This change in the permeability of the sperm membrane to ions is reflected by a change in the sperm membrane potential.
mesh_terms: D000818:Animals; D004822:Epididymis; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology*; D013081:Sperm Motility / Q000187:drug effects*; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D007476:Ionophores; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D012964:Sodium; D012413:Rubidium; D011188:Potassium