The steady-state concentration gradient for 3H-noradrenaline generated by uptake1 in the extracellular space of the rat vas deferens incubated with this amine.

The rat vas deferens was incubated with 0.2 mumol/l 3H-noradrenaline for 60 min, washed out with amine-free solution for 100 min and then prepared for autoradiography (same tissues as presented by Azevedo et al. (1990) Naunyn-Schmiedeberg's Arch Pharmacol 342:245-248). The autoradiographic images were then digitized, and grain density was determined as a function of the distance from the surface of the tissue. When neither monoamine oxidase nor vesicular uptake was impaired, i.e. under control conditions, grain density declined monophasically exponentially towards the centre of the tissue. Tis decline amounted to 0.017 micron-1 or 0.124 varicosity-1, since the average distance between varicosities was calculated to be 7.4 microns. After inhibition of monoamine oxidase and vesicular uptake the rate constant was significantly reduced, and the grain density in close proximity of the surface of the tissue was also reduced. It is proposed that the distribution of grain density observed in controls reflects the steady-state concentration gradient that is generated by uptake1 during the incubation with 3H-noradrenaline. During spontaneous efflux of 3H-noradrenaline one has to distinguish between "re-uptake of the 3H-amine into the leaking varicosity" and "uptake en passant" (during diffusion through the extracellular space). On the basis of the present results, the extent of "uptake en passant" was calculated (with a computer-assisted model) for the spontaneous efflux of heterogeneously distributed 3H-noradrenaline (after wash-out). "Uptake en passant" into varicosities located between the source of efflux and the medium amounted to about 55% of the net leakage of 3H-noradrenaline from all varicosities.(ABSTRACT TRUNCATED AT 250 WORDS)