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Biomedical subjects

T Hoshi

Publications and source records attributed to T Hoshi.

At least 163 records · Page 9Linked to original sources
PubMed1986

Ca2+- and voltage activated K+ channel in apical cell membrane of gallbladder epithelium from Triturus.

The presence of Ca2+- and voltage-activated K+ channels was directly demonstrated in the apical cell membrane of gallbladder epithelium by patch-clamp single-channel current recording. In K+-depolarized epithelial cells, negative pipette potentials induced outward current steps when the patch-pipette was filled with Na+-rich solution and these current steps were not affected by the presence or absence of Cl-. When K+-rich solution was in the pipette and K+-depolarized cells were examined, the current-voltage relations were linear with a single-channel conductance of 140 pS and polarity was reversed at 0 mV. In excised inside-out membrane patches, raising the free Ca2+ concentration of the medium facing the inner side of the membrane from 10(-7) to 10(-6) M evoked a marked increase in open state probability of the channels without affecting the elementary current steps. This suggests that intracellular Ca2+ as a second messenger plays a crucial role in the regulatory mechanism of the membrane potential by modulating the high-conductance apical K+ channels.

Animals↗
PubMed1986

A comparative study of specificity of the intestinal Na+/sugar cotransport among vertebrates.

Kt values for various monosaccharides were determined from sugar-induced increments of the transmural potentials in isolated small intestines of the goldfish, bullfrog, turtle, quail, guinea pig, rat and rabbit, and specificity patterns of the Na+/sugar cotransporters were compared among these animal species. Absolute requirement of the D-pyranose ring structure was seen in all animals. Requirements of C2-OH and C6 were strong, but not absolute, and OH groups on C3, C4, C6 and the O-atom of the pyranose ring were also suggested to participate, in some degree, in the interaction with the carrier. Comparison of the disaccharide-evoked potentials revealed that there were considerable species differences in activities of trehalase, sucrase and lactase among animals examined, but the differences were relatively small for maltase activity.

Animals↗
PubMed1986

Effects of morphine and methionine-enkephalin on the smooth muscle tonus and the contraction induced by transmural stimulation in the carp (Cyprinus carpio) intestinal bulb.

The effects of morphine and methionine-enkephalin (met-enkephalin) on the smooth muscle tonus and the contraction induced by transmural stimulation were investigated in the isolated intestinal bulb of carp in vitro. Morphine (30 nM-3 microM) and met-enkephalin (3 nM-5 microM) caused dose-dependent non-sustained contraction. Naloxone (10 nM) inhibited the contraction induced by morphine or met-enkephalin in a competitive manner. Tetrodotoxin (400 nM) or atropine (500 nM) did not inhibit the contraction induced by morphine or met-enkephalin. Cooling of the bath fluid from 20 to 10 degrees C decreased nicotine- and transmural stimulation-induced contraction. But met-enkephalin-induced contraction was not affected. Transmural stimulation-induced contraction (3 Hz) was not affected by pretreatment with morphine, met-enkephalin or naloxone. The results demonstrated that morphine or met-enkephalin caused contraction of the smooth muscle directly through the activation of opiate receptors on the smooth muscle cells and neither morphine nor met-enkephalin regulated the cholinergic neurotransmission presynaptically.

Acetylcholine↗
PubMed1986

Isolation of an antigenically unique methanogen from human feces.

A methanogenic bacterium with the morphological and physiological properties of the genus Methanobrevibacter was isolated from the feces of a Japanese man who excreted methane in his breath. Indirect immunofluorescence staining revealed that the isolate had an antigenicity unrelated to that of any known members of the genus Methanobrevibacter.

Antigen-Antibody Complex↗
PubMed1986

Sodium-independent, hydrogen ion-dependent changes in membrane potential and conductance induced by dipeptides in Triturus enterocytes.

The effects of Na+ and pH in the medium on dipeptide transport across Triturus small intestinal brush border membrane were studied electrophysiologically. Although glycylglycine exists mainly in the zwitterionic form at pH 7.30, it induced marked depolarization in the membrane potential and reduction in the input resistance both in the presence and absence of Na+ in the medium. Similar Na+-independent depolarization and resistance change were also observed with L-carnosine. On the contrary, glycine induced membrane depolarization and reduction in the input resistance only in the presence of Na+ in the medium. When pH of the medium was lowered to 6.00, the magnitude of the depolarization induced by glycylglycine increased by 33%, while at pH 8.30, it decreased by 39%. These data indicate that dipeptide transport across the intestinal brush border membrane is coupled with H+ and has no direct interaction with Na+.

Animals↗
PubMed1985

Proton-coupled transport of glycylglycine in rabbit renal brush-border membrane vesicles.

Transport of glycylglycine into rabbit renal brush-border membrane vesicles was found to be Na+-independent, H+ gradient-dependent and electrogenic. Marked overshoot uptake of the dipeptide was observed when an inward-directed proton gradient and inside-negative potential difference were imposed simultaneously across the vesicular membranes. Saturable depolarization of vesicular membranes could be demonstrated with glycylglycine by use of a fluorescent cyanine dye, di-S-C3(5). The results indicate that glycylglycine is contransported with H+ across the membranes.

Animals↗
PubMed1985

Proctolin induces rhythmic contractions and spikes in Limulus heart muscle.

The Limulus heart is neurogenic. If the cardiac ganglion is removed, all spontaneous contractions of the heart are abolished. Application of the pentapeptide proctolin (greater than 1 microM) causes the deganglionated heart muscle to beat with a frequency and amplitude slightly greater than those of a normal heart with an intact cardiac ganglion. At a proctolin concentration of 1 microM, rhythmic beating requires 2-10 min to develop, and up to 1 h of continuous washing is required to reverse the effect. A contracture often precedes the rhythmic contractions. Proctolin-induced rhythmicity occurs in the presence of tetrodotoxin (TTX) and in Na+-free saline. These effects of proctolin are not mediated by residual portions of the cardiac ganglion. Contractions are inhibited by Ca2+-free EGTA saline, CoCl2, MnCl2, and CdCl2. Proctolin causes no significant long-term changes in the myocardial resting potential or apparent input resistance. However, proctolin causes rhythmic 10- to 20-mV spikes that precede each contraction of the myocardium. Production of these spikes appears to be the mechanism by which proctolin causes rhythmic contractions in normally quiescent deganglionated myocardium of Limulus.

Action Potentials↗
PubMed1985

Neurohormonal modulation of the Limulus heart: amine actions on neuromuscular transmission and cardiac muscle.

The responses of Limulus cardiac neuromuscular junctions and cardiac muscle cells to four endogenous amines were determined in order to identify the cellular targets underlying amine modulation of heartbeat amplitude. The amines increased the amplitude of the Limulus heartbeat, with dopamine (DA) being more potent than octopamine, epinephrine or norepinephrine. The effect of DA on heartbeat amplitude was not blocked by phentolamine. DA enhanced the contractility of deganglionated heart muscle, with time course and dose-dependence similar to its effect on the intact heart. The amines also enhanced neuromuscular transmission, with time course and dose-dependence similar to their effects upon the intact heart. The amplitude of unitary excitatory junction potentials (EJPs) and frequency of miniature excitatory junction potentials (mEJPs) were increased by DA, while mEJP amplitude was unchanged. Thus DA, and probably the other amines, had a presynaptic effect. Combined actions upon cardiac muscle and cardiac neuromuscular transmission account for the ability of these amines to increase the amplitude of the Limulus heartbeat.

Amines↗
PubMed1985

Effects of Ba2+ on secretory K+ movement and electrical properties of the early distal tubule of Triturus kidney.

The mechanism of secretory supply of K+ into the diluting segment of nephron was studied in Triturus kidneys by observing Ba2+ effects on electrical phenomena related to K+ movements and other electrical properties of the segment. Ba2+ (1-2 mM) applied into the luminal fluid completely blocked K+ movement into the lumen during the stop-flow of the intraluminal K+-free solution. Also, Ba2+ inhibited transepithelial K+ diffusion potential induced by alterations in the intraluminal K+ concentration and increased transtubular resistance (Rt). A rapidly decaying time course of the K+ diffusion potential and its high peak amplitude (near the maximum expected from an imposed concentration difference) suggest that the diffusion potential was generated across the paracellular pathways. Step-changes in the Na+ concentration induced similar but smaller diffusion potentials, which were also inhibited by Ba2+. Replacement of Cl- with So2-(4) converted the time courses of both K+ and Na+ diffusion potentials to a sustained type. These suggest that the pathway has a specially high permeability to K+ and lower permeabilities to Na+ and Cl-. Triaminopyrimidine and kinetin similarly blocked K+ movement during stop-flow of a K+-free solution. The low Rt, a unique property of the segment, could be ascribed to the leakiness of the paracellular pathway from the comparison of input resistances of cells and cell surface areas between this segment and the proximal tubule. Based on these findings and other reported data, a novel mechanism of K+ supply was proposed which assumed the presence of a local pool of a high K+ concentration in the paracellular pathway and secretory movement of K+ through intercellular junctional complexes.

Animals↗
PubMed1985

Proton-coupled transport of organic solutes in animal cell membranes and its relation to Na+ transport.

Recent studies on proton-coupled transport of organic solutes in animal cell membranes were reviewed. In the intestinal and renal brush border membranes, transport of intact small peptides (di- or tri-peptides) has been established to be cotransported with H+. The peptide transport is Na+-independent, dependent on a pH gradient, electrogenic as revealed by transport-associated membrane depolarization and conductance increase, and reveals a marked overshoot uptake when a sufficiently large proton gradient is imposed across the membrane. Similar properties are found for L-lysine transport by the brush border membrane vesicles from mullet kidney and for L-leucine transport in some cultured cells. Partial involvement of H+ in Na+-dependent transport has also been reported for some organic acids, L-glutamate, and citrate. The physiological meanings of these purely H+-dependent and partially H+-dependent transports have been discussed based on available data.

Animals↗
PubMed1985

Effect of hydrogen ion-gradient on carrier-mediated transport of glycylglycine across brush border membrane vesicles from rabbit small intestine.

Glycylglycine (Gly-Gly) transport across rabbit small intestinal brush border membrane vesicles was studied in the presence and absence of a Na+ gradient or a pH gradient. The transport was found to be entirely independent of Na+ but significantly stimulated by lowering extravesicular pH (pHo). The maximum stimulation was seen at pHo 5.5, where the uptake rate was about 2-times higher than the control value. FCCP, a protonophore, abolished the stimulating effect of low pHo, and low pHo conditions without a pH gradient did not stimulate the uptake rate. Overshoot uptake of Gly-Gly was observed when a pH gradient of 2 pH units was imposed across the vesicular membrane. Valinomycin-induced inside-negative K+ diffusion potential also had a stimulating effect on the uptake, and fluorescence measurements of vesicular suspensions containing diS-C3-(5) revealed the occurrence of depolarization of the vesicular membranes when Gly-Gly was added to the suspensions. Kinetic study showed that a pH gradient caused a decrease of Kt for Gly-Gly without affecting Vmax. All the data obtained indicate that Gly-Gly transport is independent of Na+, dependent on a H+ gradient, and electrogenic, suggesting the mechanism of cotransport with H+.

Animals↗
PubMed1985

[Serum thyrotropin binding inhibitory immunoglobulin (TBII) activity before and after subtotal thyroidectomy in Grave's disease].

Serum level of TBII activity was measured in 81 patients with Graves' disease by the Smith's radioreceptor assay method and the activity more than +15% was designated as "positive". All the patients had been under medical treatment with antithyroid drugs and 71 of them underwent subtotal thyroidectomy. The negative TBII activity was seen in 4 (22%) of 18 patients in whom the duration of antithyroid drug treatment was less than 2 years and in 6 (60%) of 10 patients whose medical therapy was for more than 2 years. TBII activity was not correlated with serum MCHA-, TGHA-titers and circulating lymphocyte counts, but correlated well with the degree of lymphoid cell infiltration in the resected thyroid tissue. All the 7 patients was negative had never relapsed, but 2 of them remained at the euthyroid state 6 to 24 months after operation, 3 hypothyroid and 2 at a borderline between the normal and hypothyroid. The postoperative states of the 13 patients who showed positive TBII activity before operation were euthyroid in 7, hypothyroid in 2, borderline hypothyroid in 4 and relapse in one. A gradual decline of TBII activity following surgery was generally associated with postoperative euthyroidism. It is concluded that determination of TBII activity is of help to estimate the thyroid functional state in Graves' disease.

Graves Disease↗
PubMed1985

[Heterotopic gastric mucosa in the wall of the gallbladder: a case report and review of the literature].

A case of heterotopic gastric mucosa (pyloric gland) in the wall of the gallbladder was reported. A 58 year-old woman was admitted with a history of sudden attack of hypochondralgia radiating to the back, but she had no fever and jaundice. Ultrasonography demonstrated high echo at the neck and body of the gallbladder. Cholecystectomy was performed with a diagnosis of the gallbladder tumor containing gall stone. The surgical specimen revealed a 15 X 14 X 8mm subserosal tumor in the body and chronic cholecystitis, but showed no metaplastic differentiation in the mucosa. The cause was considered to be congenital. Heterotopic tissue in the wall of the gallbladder was very rare. In the literature, there were 29 cases of gastric mucosa and 27 cases of pancreatic tissue. The mean age of incidence were 31.9 and 42.0 year-old, respectively. There is no sex difference. The lesion was located in the cystic duct and the neck of the gallbladder in half the patients. Cholelithiasis and/or cholecystitis was complicated in many cases, and it might be associated with heterotopic tissue whereas the etiology is unknown.

Choristoma↗
PubMed1984

Facilitation of Ca2+-channel currents in bovine adrenal chromaffin cells.

Ca2+-channel currents in primary cultures of bovine adrenal chromaffin cells were studied using the whole-cell patch-clamp method. Parameters of a double-pulse protocol were systematically varied to characterize facilitation by a prepulse (P1) of Ca2+-channel current during a test pulse (P2). The pulses were usually separated by 30 msec, an interval sufficient for decay of any measurable P1 tail currents. The Ca2+-channel current amplitude during P2 increased when P1 voltage was more positive than 0 mV. The effect became progressively greater with more positive P1 voltage. With a 60-msec P1 to +80 mV, the current amplitude typically increased by 25%-35% during a 60-msec P2. Comparison of facilitated and control inward Ca2+-channel current I(V) curves showed that facilitation was also strongly dependent on P2 test voltage. Facilitation of Ca2+-channel currents is a voltage-dependent phenomenon and is not dependent on Ca2+ entry. When short repetitive voltage-clamp pulses were applied, the Ca2+-channel current amplitude increased with each pulse. This suggests that Ca2+-channel facilitation could enhance release of catecholamines from chromaffin cells during a train of action potentials.

Adrenal Medulla↗