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Biomedical subjects

Y Okajima

Publications and source records attributed to Y Okajima.

At least 109 records · Page 6Linked to original sources
PubMed1984

Origins of the transient anterior-posterior asymmetry in the frog lens fiber potential.

The origin of the transient asymmetry of intracellular resting potentials between the anterior and posterior lens fibers was investigated in the isolated American bullfrog lens by a conventional microelectrode technique. In high K+, Rb+, Cs+, or NH+4 test solution applied only to the lens anterior or posterior side, anterior fibers depolarized at a slower rate than posterior ones. After a long exposure, however, the transient potential difference disappeared. The magnitude of the depolarizations of the lens fibers was in the order of K+ greater than Rb+ greater than Cs+ greater than NH+4. The resting potentials plotted as a function of external K+ concentrations ([K]0) were in agreement with Nernst equation predictions with a slope of 58 mV/decade ion concentration change. A small Na+ permeability is unmasked at a [K]0 less than 10 mM. It was concluded that the transient difference measured in potentials of anterior and posterior lens fibers on increasing external K+, Rb+, Cs+ or NH+4 depends on the anterior epithelial cell layer, which is a diffusional barrier for ions penetrating into the lens interior.

Animals↗
PubMed1984

Comparison of the intracellular membrane potentials in crystalline lenses of various frogs.

The intracellular membrane potentials were measured in the individual lens fibers of three kinds of frogs (Rana catesbeiana, Rana pipiens japonica, Rana nigromata) by a conventional glass microelectrode technique, in which the electrode was advanced to a depth of 200 micron from the anterior surface into the lens interior. The maximum intracellular membrane potentials obtained in both anterior and posterior sides of all preparations were between -90 and -95 mV. The measured potentials were nearly close to the EK, and the membrane potentials in in vitro experiments correlated well with in vivo measurements. Low membrane potentials reported previously in various frog lenses were discussed in comparison with the present results.

Animals↗
PubMed1982

Effects of veratrine and tetrodotoxin on the frog lens potential in normal and calcium-free media.

The membrane potentials of posterior fibers of the isolated American bullfrog lens were measured in Ringer solution containing various external Ca2+ concentrations ([Ca]0) by using a conventional glass microelectrode technique. The reduction or removal of [Ca]0 evoked a rapid depolarization of the lens potential whereas the increase of [Ca]0 had almost no effects on the membrane potential. The magnitude of depolarization in Ca2+ -free medium was augmented by adding veratrine but reduced by either the addition of tetrodotoxin (TTX) or the reduction of external Na+ concentration. A slight depolarization still remained after the blockade of Na-channels by adding TTX and developed progressively during a successive exposure of lens to Ca2+-free media. It was concluded that veratrine-sensitive rapid and large depolarization in the frog lens fibers bathed in Ca2+-free medium results from a marked elevation of Na+ permeability but that the TTX-insensitive time-dependent depolarization may depend on the loss of K+ content in lens fibers.

Animals↗
PubMed1982

Effects of ouabain, lithium, and cooling on the frog lens fiber potential.

The effects of ouabain, Li+, and cooling on the lens fiber potentials i the anterior and posterior sides were investigated in American bullfrog lens mounted in a special holder by using a conventional micropipette technique. Ouabain depolarized the lens fibers in the anterior and posterior sides in a dose- and time-dependent fashion. Similarly, the fibers at both sides were depolarized in Na free, Li Ringer. The posterior fibers were depolarized faster than anterior ones during exposure to Ringer solution containing ouabain and Li+. The potential difference observed in the lens fibers of the anterior and posterior sides reduced and disappeared during a successive long exposure to ouabain and Li+. It was concluded that in the presence of ouabain and Li+ the transient potential difference between the anterior and posterior lens fibers depends on the anterior epithelial cell layer which delays the penetration of ouabain and Li+ into the lens interior, but not to the difference of total lens surface area in the anterior and posterior exposed to ouabain and Li+. Thermal dependence of the lens fiber potentials at the anterior and posterior sides was 0.78 mV/ degrees C, which is greater than the physical change of 0.2 mV/ degrees C based on the Nernst equation.

Animals↗
PubMed1981

Alteration of chemoreceptor responses and ultrastructural features of ischemic carotid body of the cat.

Effects of short-term ischemia on chemoreceptor responses to various stimuli and ultrastructural features of the carotid body of the cat were examined. Total occlusion of the arteries supplying the carotid body induced an increase in chemoreceptor discharges. After 1-hr ischemia, chemoreceptor responses to NaCN and asphyxia were markedly depressed to 10-40% of the control, while those to ACh and HCl were not greatly affected. Prolonged ischemia (2-3 hr) produced a marked decrease in responsiveness to all stimuli. One-hr ischemia induced changes in the ultrastructural appearance of the glomus cell, including a decrease in the number of dense-cored vesicles, the appearance of swollen or vacuolated mitochondria and amorphous substances, while the nerve ending showed a relatively well-preserved appearance. Prolonged ischemia (2-3 hr) produced degenerative changes both in the glomus cell and nerve ending; vacuolation, a marked decrease in electron density of cytoplasmic matrix of the glomus cell and nerve ending, and marginal shrinkage of the nuclei. The results indicate that the markedly depressed responses to NaCN and asphyxia after 1-hr ischemia are due to dysfunction of the glomus cell, while ACh and HCl, acting directly on the nerve ending which was not greatly affected by ischemia, evoked well-preserved responses in the chemoreceptors.

Animals↗
PubMed1981

Analysis of inhibitory and excitatory actions of dopamine on chemoreceptor discharges of carotid body of cat in vivo.

Chemoreceptor discharges were recorded from the carotid sinus nerve of the cat in vivo, and their frequency was used as an index of receptor activity. The effects of dopamine on chemoreceptor activity were analyzed in normal and ischemic carotid bodies. Intra-arterial injections of dopamine (DA) induced various patterns of chemoreceptor responses; simple inhibition, inhibition followed by excitation, and simple excitation, depending upon doses and the time interval between two injections. After a large dose of DA, a previous inhibitory response to DA was converted into an excitatory one. Pretreatment of the animal with reserpine (0.1 mg/kg, i.v.) or 5-hydroxydopamine (5 mg/kg, i.v.) also converted the inhibitory response to DA into the excitatory one. After haloperidol (0.1 mg/kg, i.v.), the inhibitory response to DA was completely blocked, and DA induced a dose-dependent increase in chemoreceptor discharges. After 1-hr ischemia of the carotid body, DA induced only the inhibitory response, which was blocked by haloperidol, but did not produce any excitatory responses. Results indicate that DA exerts a self-blocking action on inhibitory dopaminergic receptors which are possibly located on the nerve ending, and that DA, also acting directly on the glomus cell, would produce the chemoreceptor excitation.

Animals↗
PubMed1981

Molecular properties of cholera enteroxin.

The molecular properties of Vibrio cholerae enterotoxin obtained from two different insitutions were studied. The preparations, which were purified by different methods, showed the same physicochemical properties. Ultracentrifugal analysis showed that the toxin had a molecular weight of 79,000, a sedimentation coefficient of 5.25 S and a diffusion coefficient of 6.02 D. When the toxin was subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, the A subunit with an apparent molecular weight of 31,000-32,000 was observed. Based of these findings and the molecular weight of the B subunit of 11,604 which was calculated from its primary structure, it is proposed that holotoxin is composed of one A subunit and four B subunits.

Amino Acids↗
PubMed1980

Effect of trapidil on prostacyclin generation of arterial wall.

Prostacyclin (PGI2) has been reported to be a labile but potent inhibitor of platelet aggregation and a powerful vasodilator. This paper reports the effect of trapidil on PGI2 generation in rat aorta by means of bioassay system. The aortic ring was incubated in 0.05 M Tris HCl buffer (pH 7.5) for 10 min. This incubation medium was added into human PRP, and then incubated at 37 degrees C for 2 min., and ADP was added. PGI2 activity was assayed by the inhibitory percentage of ADP induced platelet aggregation. When the aortic ring was incubated in a medium containing trapidil, PGI2 generation was accelerated. This acceleration was inhibited by pretreatment with indomethacin. Moreover, the aortas of rats intravenously injected with 30 mg/kg of trapidil were incubated in the same way, and PGI2 activity in the medium was estimated. More potent PGI2 activity was observed in the aortas of rat treated with trapidil compared with the controls. These results indicate that acceleration of PGI2 generation from aorta by trapidil is involved in the mode of action of this drug of thrombus formation.

Animals↗
PubMed1979

Characterization of porins from the outer membrane of Salmonella typhimurium. 2. Physical properties of the functional oligomeric aggregates.

We have purified to homogeneity, from mutant strains of Salmonella typhimurium, the small oligomers of porin that confer permeability channels to artificial vesicle membranes reconstituted from phospholipids and lipopolysaccharide. The molecular weights of the porin oligomers from the strains SH5551 and SH6017 appeared to be 130000 and 125000, respectively, and those of the monomers were 41000 and 37500, respectively, when determined by sedimentation equilibrium in the presence of dodecylsulfate. It was thus concluded that the functional porin oligomers consisted of three identical subunits. The Stokes' radius of the trimer . dodecylsulfate complex was around 5 nm. The trimer bound less dodecylsulfate than the monomer. The trimer . dodecylsulfate complex retained at room temperature the native conformation of porin, which is rich in beta-structure. When the trimers were dissociated further by various treatments, only the porin monomers were recovered in significant amounts, and the permeability-conferring activity was lost simultaneously. We propose, therefore, that the trimer is the minimal functional unit of porin that is capable of forming permeability channels in the outer membrane of Salmonella typhimurium.

Cell Membrane↗
PubMed1977

Isolation of apoprotein from bovine lung surfactant material by sodium deoxycholate.

Aqueous solutions of bovine lung surfactant material were solubilized with a high concentration of sodium deoxycholate and the protein moiety could then be separated from the mixed lipid-sodium deoxycholate micelles by gel filtration in the presence of a micellar concentration of sodium deoxycholate of 10 mM. The lipid-free protein showed only one detectable peak in the gel filtrate and the sedimentation rate of this protein was 12.1 S. Sodium dodecyl sulfate disc gel electrophoresis showed essentially the same pattern as did the protein extracted directly from the bovine lung surfactant material with organic solvents, of which the major component has a molecular weight of 36 000. This protein should be the main apoprotein of lung surfactant material, and the main band in the sodium dodecyl sulfate disc gel electrophoresis, with a molecular weight of 36 000, would constitute the major protein subunit.

Animals↗