Low-affinity uptake of [3H]choline by rat neurointermediate lobe in vitro.
Uptake of [3H]choline by rat neurointermediate lobes in vitro was investigated. The rate of uptake showed saturation with concentration of [3H]choline above 120 microM. Lowering of the incubation temperature from 32 to 4 degrees C, or increasing the concentration of K+ in the incubation medium from 5 to 100 mM, diminished the rate of uptake by 83.8% (SEM 6.9%, n = 3) or 43.1% (SEM 13.5%, n = 3), respectively. Following preloading with [3H]choline, a slow efflux (1% of the content every 20 min) of [3H]radioactivity was observed from the perifused glands. This efflux was enhanced 10-fold by increasing the concentration of K+ in the perifusion medium to 100 mM. Neither the uptake of [3H]choline, nor the subsequent basal or potassium-enhanced efflux of [3H]radioactivity were affected by reducing the concentration of Na+ from 125 to 19 mM, or by including 10 microM hemicholinium-3 in the medium during preincubation and perifusion. Replacing Ca2+ by 0.5 mM EGTA during perifusion resulted in a minor decrease (28%, SEM 7.3%, n = 7) in the potassium-enhanced [3H]radioactivity efflux. This decrease occurred only in one of the two high-potassium periods during the perifusion. In conclusion, uptake of [3H]choline by rat neurointermediate lobes was due to a low-affinity, saturable mechanism, with the efflux of [3H]radioactivity most likely representing the depolarization-facilitated outflow of [3H]choline. Autoradiography of the tissue sections showed this uptake to be localized to both neuronal and glial elements of the neural lobe, in contrast to sparse labelling of pars intermedia.
Von Spreckelsen
S
S
Institute of Medical Physiology C, University of Copenhagen, Denmark.
Møller
M
M
Treiman
M
M
D000818:Animals; D001345:Autoradiography; D002794:Choline / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D009457:Neuroglia / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D002794:Choline