AJP - Gastrointestinal and Liver Physiology, Vol 241, Issue 2 137-G142, Copyright © 1981 by American Physiological Society
Functional properties of noradrenergic nervous system in rat colonic mucosa: uptake of [3H]norepinephrine
Z. C. Wu and T. S. Gaginella
The accumulation of exogenous [3H]norepinephrine ([3H]NE) by rat colonic
mucosa was studied. Uptake was linear for 10 min and reached a maximum
after 90 min. The process was concentration dependent and saturable, having
a Km of 1.67 X 10(-6) M and Vmax of 0.57 nmol.g-1.min-1. The inhibitor of
specific norepinephrine uptake, desmethylimipramine (DMI), inhibited uptake
in a concentration-dependent manner; the maximum inhibition was 81% at 10
microM. Normetanephrine also inhibited uptake at 100 microM. Reserpine, at
concentrations ranging from 10(-7) to 10(-5) M, prevented the accumulation
of [3H]NE, with maximum inhibition being 47% of control. Accumulation by
mucosa obtained from rats sympathectomized with 6-hydroxydopamine was only
33% of control; DMI did not further reduce this uptake. Colonic epithelial
cells were isolated and were found to also accumulate [3H]NE, but this
accumulation was not affected by DMI. It is concluded that rat colonic
mucosa contains noradrenergic neurons capable of accumulating exogenously
administered norepinephrine by a specific and high-affinity process. The
presence of a functional noradrenergic neural network in close association
with the epithelium suggests that this system may play a physiological role
in modulating colonic mucosal function.
