Norepinephrine uptake in canine saphenous veins in the presence and absence of halothane.

Studies were done to examine neuronal and extraneuronal uptakes of norepinephrine in canine saphenous veins and to ascertain whether these uptakes were altered by halothane. Minced vein was incubated for 1 min in Krebs-Ringer solution containing L-[ring-2,5,6-3H]-norepinephrine (1, 2.5, 6, or 12 microM). After incubation, radioactivity in tissue was measured by liquid scintillation counting. Neuronal uptake at each norepinephrine concentration was determined by the difference in norepinephrine uptake between tissues in which both neuronal and extraneuronal uptakes were operative and in tissues in which only extraneuronal uptake was operative. In time studies with 1 microM norepinephrine, neuronal uptake was still dominant at 10 min; with 12 microM norepinephrine, extraneuronal uptake predominated at all incubation periods tested. In other studies, tissues were incubated in the absence or presence of halothane (2.5%). The Km values for neuronal uptake in control and halothane-treated tissues were 2.49 and 2.32 microM, respectively. Corresponding Vmax values were 0.049 and 0.060 nMol X min-1 X 100 mg-1, respectively. No significant effect of halothane on neuronal or extraneuronal uptake could be detected.