Evidence for blood myo-inositol as a source of the epididymal secretion in the perfused cauda epididymidis of the rat

Transport of inositol into the distal cauda epididymidis of the rat

The transport of [3H]myo-inositol into the lumen of the rat distal cauda epididymidis was studied by luminal perfusion in vitro. Entry was time and tubule length-dependent and saturable transport could be demonstrated with Vmax of 237 pmol/(30 min. cm) and K+ of 1 mM. Secretion of unlabeled inositol into the epididymal lumen was maintained for 5 hours at a concentration 6 times greater than that of the bathing solution. The turnover time of the epithelial pool of inositol was 4.5 hours, from which the intracellular concentration was estimated to be 26.6 mM. Transport was not reduced by metabolic inhibitors, and it was demonstrated that exchange diffusion across the basolateral membranes could drive the uptake in this region.

Characteristics of the transport of carnitine into the cauda epididymidis of the rat as ascertained by luminal perfusion in vitro

An in vitro luminal perfusion technique was used to monitor the transepithelial movement of [3H]L-carnitine into the cauda epididymal lumen of rats. Movement of the volume marker [14C]inulin into the lumen was limited while the transport of [3H]L-carnitine was saturable and was dependent on respiratory energy. The transport of L-carnitine (50 microM) was significantly inhibited by 500 microM D-carnitine, palmitoyl L-carnitine and deoxycarnitine but not by trimethylammonium iodide, trimethyl phosphate, acetyl-L-carnitine, choline, betaine, gamma-aminobutyric acid or DL-carnitinamide. The Kt (116 microM) and Vmax (0.1 nmol/30 min/cm) for the carriers were calculated from the present data and as the Kt is about twice the normal plasma concentration of carnitine, the rate of transport by the pump is presumed to be limited by the plasma concentration.