title: Selective luminal absorption of L-carnitine from the proximal regions of the rat epididymis. Possible relationships to development of sperm motility.
abstract: The absorption of L-carnitine from the duct of the proximal regions of the rat epididymis was investigated using a stopped-flow, split-droplet microperfusion technique. L-carnitine was absorbed from the duct of the proximal caput epididymidis by a time-dependent and saturable transport system (Km = 25 micron; Vmax = 0.65 pmoles absorbed/min/mm3 tubular volume). Furthermore, absorption appeared to be primarily sodium-independent, although the existence of a minor sodium-dependent pathway cannot be ruled out. A similar transport system was not evident along the distal caput epididymidis, where absorption of L-carnitine was attributable to passive diffusion only. The inward and outward movement of L-carnitine across the epithelium of the proximal and distal caput epididymidis appears to be regulated so that the spermatozoa come into contact with high levels of L-carnitine in the distal caput region.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002331:Carnitine / Q000378:metabolism*; D004822:Epididymis / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000502:physiology; D013081:Sperm Motility
chemical_list: D012964:Sodium; D002331:Carnitine