[Axonal regeneration of retinal ganglion cells]

We have developed retinal culture system of adult mammals to investigate neural regeneration from adult retinal ganglion cells (RGC). In this culture system, neurites were regenerated from RGCs of adult retinal explants. Investigation of neurotrophic effects on the neural regeneration showed that some interleukins and neurotrophins enhanced neurite regeneration from adult rat RGCs. We also found that the adult human retina had the ability of neural regeneration and that neurotrophins enhanced this ability. A novel neurotrophic factor secreted by adult rat hepatocytes also enhanced neurite regeneration not only in adult mice but also in aged RGCs. This result indicated the novel hepatocyte secreted factor is an activator which enhances neural regeneration of the aged retina. We concluded that even adult aged RGCs had the ability of axonal regeneration after injury and that neurotrophic factors might enhanced these abilities. Therefore neurotrophic factors might have practicable applications in drug treatments for intractable disease of the neural retina and optic nerve. Future progress of neuroscience is expected to rescue the retina from various diseases, and to render possible the transplantation of the retina and optic nerve.

Clinical application of three-dimensional myocardial imaging: evaluation of efficacy of medical treatment on myocardial perfusion

To investigate the clinical applicability of the three-dimensional (3D) myocardial imaging using a newly developed system (the Application Visualization System-Medical Viewer), thallium-201 myocardial single photon emission computed tomography was performed in 19 patients with previous myocardial infarction before and after treatment with nisoldipine. We have developed a new method for automatically reconstructing 3D imaging for the stereoscopic evaluation of myocardial perfusion. The left ventricular myocardial volume with a radioisotope count > or = 50% of maximum was calculated by using the conventional surface rendering method. With these images, the effect of nisoldipine on myocardial perfusion was assessed and the myocardial volume with a radioisotope count > or = 50% of maximum was compared. In fifteen (88%) of 19 patients, myocardial perfusion increased in the infarct areas after nisoldipine treatment. Nisoldipine significantly increased the myocardial volume with a radioisotope count > or = 50% of maximum from 141 +/- 17 to 153 +/- 18 ml on the stress 3D imagings. These findings indicate that nisoldipine improved myocardial perfusion during exercise. 3D imaging provided stereoscopic assessment of the changes in myocardial perfusion following treatment with nisoldipine and also detected transient enlargement of the left ventricular lumen induced by exercise.

In-vivo clearance study of vancomycin in rats

The renal handling of vancomycin in rats and the effects of various drugs (probenecid, cimetidine and quinidine) on urinary excretion of the antibiotic were investigated by in-vivo clearance. The vancomycin-to-inulin excretion ratio (ER) was greater than unity at various infusion rates of vancomycin. Quinidine, co-administered with vancomycin, significantly decreased the total, renal and net secretory clearance of the antibiotic. Cimetidine also decreased, though not significantly, the secretory clearance of vancomycin by about 20%, but probenecid did not. These results suggested that vancomycin is secreted in renal tubules in rats, and that quinidine decreases the total clearance of vancomycin partly by inhibiting its tubular secretion in the kidney.

Cholesterol modulates organic cation transport activity and lipid fluidity in rat renal brush-border membranes

The role of cholesterol in organic cation transport was studied in rat renal brush-border membranes. H+ gradient-dependent uptake of the organic cation tetraethylammonium in brush-border membrane vesicles was stimulated by cholesterol enrichment in a dose-dependent manner. The dissipation rate of the H+ gradient, a driving force for organic cation transport in brush-border membranes, was reduced by cholesterol enrichment. Tetraethylammonium uptake in the absence of H+ gradient was also stimulated by cholesterol enrichment. These findings indicate that cholesterol modulates tetraethylammonium uptake by affecting the intrinsic activity of the organic cation transporter and the H+ gradient dissipation rate. Therefore, cholesterol content should be an important determinant for organic cation transport in renal brush-border membranes.

Induction of hydrotropism in clinorotated seedling roots of Alaska pea, Pisum sativum L

Roots of the agravitropic pea (Pisum sativum L.) mutant ageotropum show positive hydrotopism, whereas roots of Alaska peas are hydrotropically almost non-responsive. When the gravitropic response was nullified by rotation on clinostats, however, roots of Alaska peas showed unequivocal positive hydrotropism in response to a water potential gradient. These results suggest that roots of Alaska peas possess normal ability to respond hydrotropicallly and their weak hydrotropic response results from a counteracting effect of gravitropism.

Expression of low-molecular-weight kininogen mRNA in human fibroblast WI38 cells

Expression of the low-molecular-weight kininogen (L-kininogen) mRNA in the human fibroblast cell line WI38 was examined by means of the reverse-transcription polymerase chain reaction and Southern blotting using human L-kininogen cDNA as a probe. The results demonstrated that WI38 fibroblasts expressed L-kininogen mRNA and that the expression was stimulated by 1 mM dibutyryl cAMP or 10 microM prostaglandin E2. Dexamethasone (1 microM) inhibited the stimulatory effect of prostaglandin E2. These results suggest that human fibroblasts supply L-kininogen, a protein precursor of the inflammatory mediator kinins, to connective tissues in response to inflammatory stimuli and that glucocorticoids may exert the antiinflammatory effect in part by inhibiting the local production of L-kininogen.

Effect of CYP2C polymorphisms on the pharmacokinetics of phenytoin in Japanese patients with epilepsy

We examined the effect of CYP2C9/19 polymorphisms on the pharmacokinetics of phenytoin in 17 Japanese patients with epilepsy. The maximal elimination rate (Vmax) of phenytoin was slightly decreased (up to 14%) in patients with CYP2C19 mutations for the defective allele. The Vmax values in patients with a CYP2C9 mutation for the heterozygous Ile/Leu359 allele were 40% lower than those in patients with wild-type CYP2C9 for the homozygous Ile359 allele. These findings suggested that the genetic polymorphism of CYP2C isoenzymes plays an important role in the pharmacokinetic variability of phenytoin, and that the mutation in CYP2C9 proteins is a determinant of impaired metabolism of the drug.

Regulation of p-aminohippurate transport by protein kinase C in OK kidney epithelial cells

We studied the effect of phorbol 12-myristate 13-acetate (PMA), a phorbol ester which activates protein kinase C, on p-aminohippurate (PAH) transport in OK cells. PMA (10(-7) M) almost completely inhibited the transcellular transport of PAH across OK cell monolayers from the basal to the apical side, as well as the accumulation of PAH in the cells. The uptake of PAH across the basolateral membrane of OK cells was inhibited by PMA in a time-and dose-dependent fashion. Exposing the cells with other protein kinase C activators such as active phorbol esters and diacylglycerols also resulted in a significant inhibition of basolateral PAH uptake, but the inactive phorbol ester, 4 alpha-phorbol 12,13-didecanoate, had no effect. The inhibition of basolateral PAH uptake by PMA was blocked by staurosporine, an inhibitor of protein kinase C. Cycloheximide, actinomycin D, colchicine, and cytochalasin D did not affect the inhibitory effect of PMA on basolateral PAH uptake. These results suggested that the PAH transport system in OK cells is under the regulatory control of protein kinase C.

cDNA cloning and functional expression of a novel rat kidney organic cation transporter, OCT2

A cDNA encoding a novel organic cation transporter, designated as OCT2 was isolated from the rat kidney. The rat OCT2 cDNA (2,205 bp) had an open reading frame encoding for a 593-amino acid protein (calculated molecular mass of 66 kDa) which shows 67% identity with the rat OCT1. Northern hybridization and reverse transcription-PCR analyses revealed that the rat OCT2 mRNA transcript was expressed predominantly in the kidney, at higher level in the medulla than in the cortex, but this transcript was not detected in the brain, heart, lung, liver, small intestine or spleen. When expressed in Xenopus oocytes, rat OCT2 stimulated the uptake of tetraethylammonium, and the uptake was markedly inhibited by the presence of cimetidine, procainamide and quinidine. These findings suggest that OCT2 is responsible for the transport of cationic drugs in the kidney.

[An application of semiquantitative analysis of pulmonary scintigram to pulmonary tuberculosis sequelae]

We performed ventilation-perfusion scintigraphy in 13 patients with pulmonary tuberculosis sequelae and 21 with chronic obstructive pulmonary disease. We used 99mTc-MAA for perfusion scintigram and 133Xe gas for ventilation scintigram. We added the radioactivities during the rebreathing phase of the ventilation scintigram to make a computerized image of the lung volume. Regions of interest (ROIs) were derived from radioactivities on each image. ROIs included each whole lung on lung volume (L) image and areas where radioactivity was greater than 70% of the highest radioactivity on perfusion (P70) image. We counted the area of ROIs on L and P70, and used the ratio of perfusion to lung volume (P70/L) as a parameter of pulmonary perfusion. P70/L in patients with pulmonary tuberculosis sequelae was significantly higher than that in those with COPD. This suggested that the area of high pulmonary perfusion is larger in the patients with pulmonary tuberculosis sequelae as compared with those with COPD.

Modulation of organic cation transport and lipid fluidity by benzyl alcohol in rat renal brush-border membranes

PURPOSE

Organic cations are actively transported in renal brush-border membranes (BBM) by the H+/organic cation antiport system. In the present study, we investigated the relationship between membrane fluidity and organic cation transport in the BBM.

METHODS

The effects of benzyl alcohol, a membrane fluidizing agent, on the organic cation tetraethylammonium (TEA) uptake were studied using renal BBM vesicles isolated from rat kidney. BBM fluidity was assessed by fluorescence polarization technique.

RESULTS

H+ gradient-dependent uptake of TEA in BBM vesicles was inhibited by benzyl alcohol in a dose-dependent manner, with an apparent half inhibitory concentration of 18mM. The decrease in fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene in BBM, which represents the increase in membrane fluidity, was correlated with the decrease in TEA transport activity. The dissipation rate of H+ gradient, a driving force for organic cation transport in BBM, was increased by benzyl alcohol. In addition, H+ gradient-independent TEA-TEA exchange was also inhibited by benzyl alcohol. These findings indicate that benzyl alcohol inhibits the uptake of TEA by affecting the intrinsic activity of the organic cation transporter and the H+ gradient dissipation rate.

CONCLUSIONS

The membrane fluidity should be an important determinant for organic cation transport in renal BBM.

[High uptake of N-isopropyl-p-[123I]-iodoamphetamine (123I-IMP) demonstrated by dynamic SPECT in some cases of glioma]

Selective high uptake of N-isopropyl-p-[123I]-iodoamphetamine (123I-IMP) in the brain tumors is not common, the mechanism of uptake in the brain tumor is not yet clearly understood. Among 26 cases of gliomas investigated by dynamic SPECT, 4 cases including 2 cases of anaplastic astrocytoma and 2 cases of oligodendroglioma, showed high uptake of 123I-IMP. New three detector type camera which enables us to investigate rapid successive scanning, was used in our study. In dynamic SPECT, 15 successive scans of 2 minutes interval were made for 30 minutes after administration of 123I-IMP. In addition, quick dynamic SPECT was tried in 2 cases, in which 10 quick successive scans of 24 seconds interval were investigated for initial 4 minutes immediately after administration of 123I-IMP. Radioactivity in the region of interest inside the tumor (T) and radioactivity of the corresponding site in the contralateral hemisphere (C) was measured respectively, and T/C ratio was calculated. Time course change of radioactivity (time activity curve: TAC) was analyzed in all cases. Radioactivity was always higher in the tumor and the average T/C ratio was 1.40. TAC showed rapid increase of 123I-IMP in the tumor during initial 2 minutes after administration and keeping its high plateau level for 30 minutes. Angiography in these cases revealed a remarkable tumor stain. On the other hand, these gliomas showed no or slight enhancement effect in CT or MRI. These findings are interpretable as that early high uptake of 123I-IMP in some gliomas is attributable to an increased vascular bed and blood flow with no or minimal derangement of blood brain barrier in these tumors.

Fibroblasts synthesize kininogen in response to inflammatory mediators

Mouse fibroblasts in vitro secret kininogen (KGN). Rat fibroblasts also synthesized and secreted T-KGN in vitro. KGN production by these fibroblasts is greatly stimulated by dibutyryl cAMP, prostaglandin E2 and tumor necrosis factor. Human fibroblast WI-38 cells also express the L-KGN gene, which was stimulated by dibutyryl cAMP and prostaglandin E2. These results demonstrate that fibroblasts express the KGN gene, and suggest that the expression is regulated by inflammatory mediators. RT-PCR, using specific primers for the T-KGN and L-KGN genes, reveals that the rat hind-paw express both T- and L-KGN mRNAs, and the expression of both KGN mRNAs was increased in the hind-paw 24 h after inducing inflammation by injecting Freund's complete adjuvant into the paw. Thus, it is suggested that local connective tissues express the KGN gene, and that the expression is enhanced under pathological conditions, such as inflammation.

Expression of three members of the calcium-dependent protein kinase gene family in Arabidopsis thaliana

Calcium-dependent protein kinases (CDPKs) belong to a unique family of enzymes containing a single polypeptide chain with a kinase domain at the amino terminus and a putative calcium-binding EF hands structure at the carboxyl terminus. From Arabidopsis thaliana, we have cloned three distinct cDNA sequences encoding CDPKs, which were designated as atcdpk6, atcdpk9 and atcdpk19. The full-length cDNA sequences for atcdpk6, atcdpk9 and atcdpk19 encode proteins with a molecular weight of 59343, 55376 and 59947, respectively. Recombinant atCDPK6 and atCDPK9 proteins were fully active as kinases whose activities were induced by Ca2+. Biochemical studies suggested the presence of an autoinhibitory domain in the junction between the kinase domain and the EF hands structure. Serial deletion of the four EF hands of atCDPK6 demonstrated that the integrity of the four EF hands was crucial to the Ca2+ response. All the three atcdpk genes were ubiquitiously expressed in the plant as demonstrated by RNA gel blot experiments. Comparison of the genomic sequences suggested that the three cdpk genes have evolved differently. Using antibodies against atCDPK6 and atCDPK9 for immunohistochemical experiments, CDPKs were found to be expressed in specific cell types in a temporally and developmentally regulated manner.

Population pharmacokinetics of phenytoin in Japanese patients with epilepsy: analysis with a dose-dependent clearance model

The population pharmacokinetic parameters of phenytoin were estimated using routine therapeutic drug monitoring data from 116 epileptic patients. The 531 serum concentration values at steady-state after repetitive oral administration were analyzed using a nonlinear mixed effects model (NONMEM) program designed for estimation of population pharmacokinetic parameters. A one-compartment model with dose-dependent clearance was used for the pharmacokinetic analysis of phenytoin. The volume of distribution (V) was estimated to be 1.231/kg in a typical 42-kg patient, assuming that the bioavailability of orally administered phenytoin is 100%. The maximal elimination rate (V(max)) and the Michaelis-Menten constant (K(m)) were 9.80 mg/d/kg and 9.19 micrograms/ml, respectively. The parameter of power function of weight to adjust V and V(max) was estimated to be 0.463. In addition, K(m) for phenytoin appeared to be 16% increased in patients receiving zonisamide concurrently. The population pharmacokinetic parameters of phenytoin will be useful for designing dosage regimens in epileptic patients.