Role of phospholipase A2 in hypoxia-induced renal cell injury

The present study was designed to assess the roles of PLA2 activation and arachidonic acid (AA) metabolites in hypoxia-induced renal cell injury. Hypoxia increased LDH release in a dose-dependent manner in rabbit renal cortical slices, and this increase was significant after 20-min hypoxia. The hypoxia-induced LDH release was prevented by amino acids, glycine and alanine, and extracellular acidosis (pH 6.0). Buffering intracellular Ca2+ by a chelator, but not omission of Ca2+ in the medium produced a significant reduction in hypoxia-induced LDH release. The effect of hypoxia was blocked by PLA2 inhibitors, mepacrine, butacaine, and dibucaine. A similar effect was observed by a 85-kD cPLA2 inhibitor AACOCF3. AA increased hypoxia-induced LDH release, and albumin, a fatty acid absorbent, prevented the LDH release, suggesting that free fatty acids are involved in hypoxia-induced cell injury. These results suggest that PLA2 activation and its metabolic products play important roles in pathogenesis of hypoxia-induced cell injury in rabbit renal cortical slices.

Effects of ethanol on Na+-dependent solute uptake in rabbit renal brush-border membrane vesicles

This study was undertaken to examine the effect of ethanol on Na+-dependent transport systems (glucose, phosphate, and dicarboxylate) in renal brush-border membrane vesicles (BBMV). Ethanol inhibited Na+-dependent uptakes of glucose, phosphate, and succinate in a dose-dependent manner, but not the uptakes of Na+-independent. The H+/TEA antiport was reduced by 8% ethanol. Kinetic analysis showed that ethanol caused a decrease in Vmax of three transport systems, leaving Km values unchanged. Ethanol decreased phlorizin binding, which was closely correlated with the decrease in Vmax of Na+-glucose uptake. These results indicate that ethanol inhibits Na+-dependent uptakes of glucose, phosphate, and dicaboxylate and that the reduction in Vmax of Na+-glucose uptake is caused by a decrease in the number of active carrier proteins in the membrane.

Increase of intracellular Ca2+ concentration by Vibrio vulnificus cytolysin in rat platelets; triggering mechanism of platelet cytolysis

Vibrio vulnificus cytolysin caused platelet cytolysis and increased intracellular calcium concentration ((Ca2+))i) of rat platelets in a concentration-dependent manner. In the presence of V. vulnificus cytolysin (3 HU/ml), lactate dehydrogenase (LDH) activity was increased from 1.3+/-0.4% of control to 64.3+/-3.4% in platelet suspension buffer. In Ca2+-free platelet suspension buffer, however, V. vulnificus cytolysin did not induce (Ca2+)i increase and LDH release. Addition of EGTA (2 mM) to suspension buffer after the initial Ca2+ influx reversed (Ca2+)i to the control level. However, a Ca2+ channel blocker verapamil (20 muM) or mefenamic acid (20 muM) did not inhibit V. vulnificus cytolysin-induced (Ca2+)i increase and LDH release. Divalent cations such as Co2+, Cd2+ or Mn2+ (2 mM each) also did not alter V. vulnificus cytolysin-induced (Ca2+)i increase and LDH release. V. vulnificus cytolysin (3 HU/ml)-induced calcium influx was completely blocked by lanthanum (2 mM). Lanthanum (2 mM) also completely blocked V. vulnificus cytolysin (3 HU/ml)-induced LDH release. Osmotic protectants such as, raffinose, sucrose or PEG600 (50 mM each) did not inhibit the lytic activity of V. vulnificus cytolysin. In conclusion, lanthanum sensitive Ca2+ influx plays a significant role in Vibrio vulnificus cytolysin-induced platelet cytolysis and thrombocytopenia in V. vulnificus infection.

Assessment of flavin-containing monooxygenase (FMO) activity by determining urinary ratio of theobromine and caffeine in a Korean population after drinking a cup of coffee

To examine individual variation in drug metabolism catalyzed by flavin-containing monooxygenase (FMO), 179 Korean volunteers' urinary molar concentration ratio of theobromine (TB) and caffeine (CA) was determined. Their urine was collected for 1 hr (between 4 and 5 hrs) after they drank a cup of coffee containing 115 mg CA and analyzed by an HPLC system. The lowest TB/CA ratio obtained was 0.40, the highest ratio was 15.17 (38-fold difference), and the median ratio for all subjects was 1.87. The mean was 2.66 with 2.36 S.D.. In 134 nonsmokers, the mean ratio was 2.35 +/- 1.93, that of 51 males was 2.30 +/- 2.26 and 83 females was 2.37 +/- 1.85, respectively. There was no significant gender difference in the obtained TB/CA ratio (Mann-Whitney test; p=0.518). There were no smokers among the 83 female volunteers. In the remaining 96 male subjects, the ratio obtained in 51 nonsmokers was 2.30 +/- 2.06 and that of 45 smokers was 3.62 +/- 3.19. This indicated that the TB/CA ratio was increased significantly in smokers (p=0.007). However, when the TB/CA ratios (FMO activity) obtained in all 179 Korean volunteers are compared with the urinary concentration ratios of paraxanthine (PX) plus 1,7-dimethylurate (17U) to CA (CYP1A2 activity), there was a weak but significant correlation (Pearson's correlation coefficient test; r2=0.28, p<0.0001). This indicates that, although the urinary TB/CA ratio mostly represents FMO activity, minor contribution by CYP1A2 activity cannot be ignored. In conclusion, the FMO activity measured by taking the urinary TB/CA ratio from normal healthy Korean volunteers shows marked individual variations without significant gender differences and the increased TB/CA ratio observed in cigarette smokers may have been caused by the increased CYP1A2 activity.

Comparative effects on secretion of LH, FSH, prolactin, and testosterone by chronic and direct hypothalamic administration of nonylphenol to adult male rats

Nonylphenol (NP) is a widespread environmental pollutant that has been shown to exert both toxic and estrogenic effects on mammalian cells. As the effects of NP on the reproductive system of adult male vertebrates are virtually unknown, we investigated not only the changes of reproductive hormone secretion in serum after chronic exposure to NP but also, in order to identify the site of its action, the reproductive hormone secretion in serum 48 hours after microinfusion of NP within hypothalamic preoptic area (POA). In the chronic exposure, the luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone in serum were decreased but prolactin (PRL) concentrations were increased. The LH, FSH, and testosterone in serum were decreased through the direct infusion of NP into POA, while there was no difference in mean serum prolactin between NP and control groups. These observations suggest that NP as endocrine disruptor has modulatory effects on hypothalamo-pituitary-gonadalaxis and that the site of action of NP could be hypothalamic POA.

Thyroid hormone-induced alterations of Ca2+-ATPase and phospholamban protein expression in cardiac sarcoplasmic reticulum

Alterations of cardiovascular function associated with various thyroid states have been studied. In hyperthyroidism left ventricular contractility and relaxation velocity were increased, whereas these parameters were decreased in hypothyroidism. The mechanisms for these changes have been suggested to include alterations in the expression and/or activity levels of various proteins; alpha-myosin heavy chain, beta-myosin heavy chain, beta-receptors, the guanine nucleotide-binding regulatory protein, and the sarcolemmal Ca2+-ATPase. All these cellular alterations may be associated with changes in the intracellular Ca2+ concentration. The most important regulator of intracellular Ca2+ concentration is the sarcoplasmic reticulum (SR), which serves as a Ca2+ sink during relaxation and as a Ca2+ source during contraction. The Ca2+-ATPase and phospholamban are the most important proteins in the SR membrane for muscle relaxation. The dephosphorylated phospholamban inhibits the SR Ca2+-ATPase through a direct interaction, and phosphorylation of phospholamban relieves the inhibition. In the present study, quantitative changes of Ca2+-ATPase and phospholamban expression and the functional consequences of these changes in various thyroid states were investigated. The effects of thyroid hormones on (1) SR Ca2+ uptake, (2) phosphorylation levels of phospholamban, (3) SR Ca2+-ATPase and phospholamban protein levels, (4) phospholamban mRNA levels were examined. Our findings indicate that hyperthyroidism is associated with increases in Ca2+-ATPase and decreases in phospholamban levels whereas opposite changes in these proteins occur in hypothyroidism.

THE CULTURE OF PROXIMAL TUBULE CELLS OF RABBIT KIDNEY / 解剖学报

It is a new approach to investigate the ultrastructure, function and metabolism of each segment of uriniferous tubule using dual environment culture chambers (DECC). In the present study the DECC culture of proximal tubule cells was undertaken with millcell-HA culture insert in the mixed medium of Ham's F12 and Dulbecco's modified Eagle's medium.A monolayer of proximal tubule cells was obtained in the medium mixed by constant bubling of oxygen at 3 weeks after seeding. Transmission electron microscopy revealed the cuboidal cells with microvilli, abundant mitochondria, vacuoles, lysosomes, and irregular plasma membrane infoldings. Also, the monolayer exhibited active metabolism from the release of ~(14)C-I-carbon dioxide and absorption ability of ~(14)C-I-glucose across the cultured monolayer. In addition, the culture procedure has been introduced in detail.