Nicotinic acid transport mediated by pH-dependent anion antiporter and proton cotransporter in rabbit intestinal brush-border membrane

In order to determine whether the vitamin nicotinic acid is absorbed via an anion antiporter, intestinal epithelial cell membrane transport mechanisms for nicotinic acid were characterized using isolated rabbit jejunal brush-border membrane vesicles. The uptake of nicotinic acid by the membrane vesicles showed an overshoot phenomenon in the presence of an outwardly directed bicarbonate gradient or an inwardly directed proton gradient and the uptakes were two times and six times greater, respectively, than that in the absence of any ion gradient. The bicarbonate-dependent initial uptake of nicotinic acid was increased at acidic pH, showing pH-dependent transport activity. An inhibitor of anion transport, 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid, specifically reduced bicarbonate-dependent transport of nicotinic acid. The initial uptakes of nicotinic acid via the anion antiporter and the proton cotransporter were specifically inhibited by monocarboxylic acids such as acetic acid, benzoic acid, D- and L-lactic acid, pravastatin and valproic acid, but not by di- or tricarboxylic acids, bile acids or amino acids. Nicotinic acid uptake activity was, furthermore, expressed in a Xenopus laevis oocyte system after injection of messenger RNA (mRNA) derived from rabbit intestinal epithelial cells. These observations demonstrate that nicotinic acid is absorbed by two independent active transport mechanisms from small intestine, i.e. a proton cotransporter and an anion antiporter. The pH-dependence observed in the intestinal absorption of nicotinic acid might, therefore, be ascribed partly to pH-sensitive and partly to carrier-mediated transport mechanisms in the brush-border membrane.     

Drivers' Mental Representation of Travel Time and Departure Time Choice in Uncertain Traffic Network Conditions

The decisions drivers make, such as choice of route or departure time, constitute typical decision making under uncertainty. Drivers' decision making has been studied within the framework of expected utility theory. However, empirical decisional phenomena violating the premise of expected utility theory have been observed repeatedly. These findings have indicated that decision making is critically affected by the decision frame. It has also been pointed out that the uncertainty of outcome is perceived as an interval of possible resultant values. Based on these findings, we propose hypotheses that: (1) a driver perceives an uncertain travel time as an interval, and (2) a driver decides on a departure time based on a decision frame edited by this interval. To test these hypotheses, we collected data on drivers' departure time choice behavior, n = 335. Decisional phenomena found in this study confirm our hypotheses.     

Vascularized fibular graft for reconstruction of the wrist after excision of giant cell tumor

Seven patients with a giant-cell tumor involving the distal end of the radius were treated with en bloc resection and reconstruction with a free vascularized fibular graft. Two patients with stage 2 disease of Enneking's surgical staging and grade 2 of Campanacci's radiographic grading system were reconstructed with an articular fibular head graft. Five patients with stage 3 and grade 3 disease underwent wrist arthrodesis using fibular shaft transfer. There was radiographic evidence of bone union at the host-graft junctions in all cases. No local recurrence was seen in any of the patients at the most recent follow-up examinations. There were six good and one excellent functional results. Wrist arthroplasty using a vascularized fibula head graft is the best procedure for a stage 2 or grade 2 giant-cell tumor of the distal end of the radius. In cases of stage 3 or grade 3 disease, wrist arthrodesis using a vascularized fibular shaft graft is indicated.     

A case of congenital intraspinal neuroblastoma

A case of congenital intraspinal neuroblastoma with paraplegia in a newborn is described, and a review of previously reported cases is presented. Calcification within the spinal canal and abdominal mass was noted. At age 75 days, the patient underwent a resection of almost the entire retroperitonial tumor. A magnetic resonance scan showed hepatic metastasis, and chemotherapy was changed to a more intensive regimen. The liver metastasis disappeared; however, neurological signs persisted. A literature review of 38 cases showed 26 patients had a laminectomy and 12 patients did not. Treatment with or without laminectomy was associated with a poor prognosis for neurological recovery, suggesting cord compression must occur antenatally, and irreversible damage occurs before birth. Congenital intraspinal neuroblastoma has a relatively good prognosis (survival rate, 91.9%), although complete neurological recovery is highly unusual. Based on these findings, the authors conclude that a laminectomy is not indicated for those patients.     

Effect of fatty acids on lipid and apoprotein secretion and association in hepatocyte cultures

Increasing availability of free fatty acids (FFA) to liver results in enhanced rates of secretion of triglycerides in lipoproteins. However, as FFA uptake increases, triglyceride secretory rates reach a plateau and esterified fatty acids accumulate intracellularly, suggesting that something is limiting lipid transport out of the liver. One possibility could be the limited availability of apoproteins. To test this hypothesis, primary rat hepatocytes in culture were incubated with increasing amounts of FFA (0-2.1 mumol/dish) and the amounts of lipids and apoproteins inside the cells and in culture media were measured; the latter by specific radioimmunoassays. Media also were fractionated on Sepharose 2B and 6B columns and the elution profiles of apoproteins were obtained. With exposure to increasing amounts of free fatty acids, hepatocytes took up more fatty acids and intracellular levels of triglycerides rose (from 71 to 146 micrograms/mg cell protein). Concomitantly, media triglycerides nearly doubled (31 to 51 micrograms/mg). Incorporation of [3H]glyceride into cellular and media triglyceride also rose. However, levels of apoproteins A-I, B, C-III3, and E in cells and media were unchanged. The increasing amounts of triglycerides in media were present in larger particles, as demonstrated on gel permeation chromatography. The elution profiles of apoproteins B, C-III3, and E were altered in that a greater proportion of the apoproteins eluted with larger particles. Similar results were obtained when hepatocytes were preloaded with increasing amounts of FFA over 12 h and analyses of cells and media were carried out 8 and 22 h after removal of fatty acids from the media. During loading of cells, accumulation of cellular triglycerides was directly related to media FFA concentrations. During unloading, triglyceride secretory rates were related to cellular triglyceride levels. At higher triglyceride secretory rates larger particles were secreted and a greater proportion of apoproteins was associated with the larger particles, but total amounts of apoproteins in the system did not change. These data lead us to suggest that enhanced rates of apoprotein synthesis need not occur in the response to acute changes in hepatic lipid transport, rather, increased secretion of lipid is brought about by augmented intracellular lipid apoprotein association.     

ON THE SPECIFIC RESISTANCE OF CAKES OF MICROORGANISMS

The mean specific resistance of the cakes of various microorganisms was evaluated by measurement of either a change in the amount of permeate with time or of steady-state flux under constant pressure. The mean specific resistance was different with different shapes and sizes of microorganisms. The large differences arose from different packing structures of the cake. The effect of a filter aid on the filtration rate and cake structure was studied experimentally and theoretically. The effects of a filter aid were best explained by a series model, in which a cake layer composed of microbial cells and a layer of randomly distributed microbial cells and filter aid are packed on the membrane surface in series with respect to the directions of permeation.     

Nonlinear magnetic levitation control by four-point attraction

Rubber components of production equipment are a significant source of contamination in the fabrication of VLSI devices and other semiconductor products. One approach to solving this problem is to use a magnetic levitation system for noncontact transfer. The force nonlinearity of magnetic circuits presents a problem, particularly when the gap between the magnets and the levitated vehicle is small. Linearization methods that allow effective control do exist, but in this paper an alternative method not based on linearization is proposed. The design involves magnetic levitation control by 4-point attraction. The experimental results indicate that the idea is an effective one.     

Gene-dose effect on carnitine transport activity in embryonic fibroblasts of JVS mice as a model of human carnitine transporter deficiency

Recently, the marked decline in renal carnitine reabsorption has been thought to account fotr the systemic carnitine deficiency in juvenile visceral steatosis (JVS) mice. We have conducted a kinetic analysis using embryonic fibroblasts derived from normal, heterozygous, and homozygous jvs mice and found that the high-affinity carnitine transporter (Km = 5.5 microM), which shows Na+ and temperature dependency and stereospecificity, is defective in homozygous jvs mice. Moreover, a gene dose-dependent decrease of carnitine transport activity, which was due to a decrease in the number of the transporter molecules, was found in heterozygous jvs mice. Similar phenomena have been observed in human primary carnitine deficiency. Therefore, JVS mice may be useful for understanding this extremely rare human hereditary disorder.