Transfer of 45Ca and 36Cl at the blood-nerve barrier of the sciatic nerve in rats fed low or high calcium diets.
Unidirectional fluxes of 45Ca, 36Cl, and of [3H]mannitol from blood into the sciatic nerve and cerebral cortex were determined from 5- and 15-min uptakes of these tracers after an intravenous (i.v.) bolus injection in awake rats. Rats were fed diets for 8 wk, that had either a low (0.01% wt/wt), normal (0.67%), or high (3%) Ca content. Plasma [Ca] was 32% less and 11% more in rats fed low (LOCA) and high Ca diets (HICA), respectively, than in rats fed a normal Ca diet (CONT). The mean permeability-surface area product (PA) of 45Ca at the blood-nerve barrier was about eightfold higher than at the blood-brain barrier in the same animals and did not differ significantly between groups (greater than 0.05). Mean PA ratios of 45Ca/36Cl for the blood-nerve and blood-brain barriers in CONT rats, 0.52 +/- 0.04 and 0.40 +/- 0.02, respectively, were not significantly different from corresponding ratios in LOCA and HICA groups, and corresponded to the aqueous limiting diffusion ratio (0.45). Our results show no evidence for concentration-dependent transport of Ca over a plasma [Ca] range of 0.8-1.4 mmol/liter at the blood-nerve barrier of the rat peripheral nerve, and suggest that Ca and Cl exchange slowly between nerve and blood via paracellular pathways.
Wadhwani
K C
KC
Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892.
Murphy
V A
VA
Rapoport
S I
SI
D000818:Animals; D001812:Blood-Brain Barrier / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D002118:Calcium / Q000097:blood / Q000134:cerebrospinal fluid / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002136:Calcium, Dietary / Q000494:pharmacology*; D002712:Chlorides / Q000378:metabolism*; D002713:Chlorine; D006706:Homeostasis / Q000187:drug effects; D008297:Male; D008353:Mannitol / Q000378:metabolism; D010539:Permeability / Q000187:drug effects; D011868:Radioisotopes; D051381:Rats; D011919:Rats, Inbred Strains; D012584:Sciatic Nerve / Q000378:metabolism*
D002132:Calcium Radioisotopes; D002136:Calcium, Dietary; D002712:Chlorides; D011868:Radioisotopes; D008353:Mannitol; D002713:Chlorine; D002118:Calcium