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Volume 25 (1975)
- Issue 6 Pages 665-
- Issue 5 Pages 563-
- Issue 4 Pages 401-
- Issue 3 Pages 241-
- Issue 2 Pages 93-
- Issue 1 Pages 1-
Volume 25, Issue 6
Displaying 1-9 of 9 articles from this issue
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I. CHOWERS, N. CONFORTI, E. SUPERSTINE1975 Volume 25 Issue 6 Pages 665-676
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSRabbits exposed for one hour to a temperature of 40°C and 35-37% humidity showed elevated plasma osmolality and pH. Most of the animals were not able to withstand the heat. Dexamethasone-treated rabbits under the same conditions withstood the heat better and their plasma pH and osmolality remained constant. Metopirone-treated rabbits withstood the heat and showed a rise in plasma osmolality and a slight change in plasma pH. The highest rise in rectal temperature was observed in the metopirone-treated rabbits. Only the untreated animals were unable to regain pre-exposure rectal temperature. The results suggest that high levels of glucocorticosteroids enhance neurogenic and metabolic mechanisms which have protective functions during acute exposure to heat.View full abstractDownload PDF (1176K) -
Takuro OSA1975 Volume 25 Issue 6 Pages 677-691
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSEffects of Mg ion, low temperature and 2, 4-dinitrophenol on the K contracture were investigated in pregnant rat uteri. At 36-38°C, the addition of Mg ions increased the amplitude of tonic contraction when the isotonic K media contained 2.2mM Ca (potentiating effect), whereas the same procedure decreased the amplitude of the tonic contraction when the media contained 0.22mM Ca (inhibitory effect). When the muscle strip was loaded with Mg ion by exposing it previously to a Locke-Ringer solution containing 10mM Mg ions for 20-30min, the potentiating effect of Mg ion was nearly abolished but the inhibitory effect persisted. The amplitude of the tonic contraction was reduced, and the potentiating effect of the Mg ion was depressed at lower temperatures. The inhibitory effect persisted at low temperatures. The time course of relaxation of the phasic contraction consisted of two exponentials, the initial one fast and succeeding one slow. The effect of Mg on the relaxation during the initial phase was variable, but the succeeding one always became slower when Mg ions were added. The initial phase of the relaxation became slower at lower temperatures. However, the succeeding phase became faster. The above experimental results were interpreted to suggest that the sites of Mg action were two, one being at the outer surface of the membrane competing for occupation with Ca ions, and the other within or at the inner surface of the membrane regulating the amount of bound Ca which is in turn utilized to evoke contraction. The latter is probably mediated by metabolic processes.View full abstractDownload PDF (1465K) -
Toshio YAMAGUCHI1975 Volume 25 Issue 6 Pages 693-704
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSTo clarify the detailed mechanism of caffeine-induced twitch potentiation in single muscle fibers isolated from semitendinosus muscles of the frog, the fibers were stimulated by the different patterns of repetitive pulses. On rapid application of 1mM caffeine to the fiber, progressive potentiation of the twitches were observed in all cases, and as the stimulation frequencies were increased (from 0.1 to 5Hz), the periods taken to the fully potentiated twitch were shortened from 23sec to about 4 sec on the average. If the repetitive stimulations at 2Hz were stopped for a while during the potentiating phase of an ordinarily stimulated fiber, the fully potentiated twitch occurred later than that observed in the ordinarily stimulated fiber. It was confirmed that caffeine did not have any significant effects on both the features of the action potential and the magnitude of the resting potential of the single muscle fiber. These results indicate that the responses of the fiber themselves play an important role in the caffeine-induced twitch potentiation, and its mechanism was discussed with reference to the behavior of the fiber membrane and the triadic junction through which caffeine is assumed to act on the sarcoplasmic reticulum.View full abstractDownload PDF (3066K) -
Masayasu HIRAOKA, Mari HIRAOKA1975 Volume 25 Issue 6 Pages 705-717
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSThe role of positive dynamic current (chloride current) on action potentials of cardiac Purkinje fibers was studied. The removal of most extracellular chloride ions brought about a slowing of the repolarization process. The most prominent effect was noted on the initial rapid repolarization (phase 1) of the action potentials. Purkinje action potentials showed marked and consistent slowing of phase 1 with increasing rate of stimulation. The removal of [Cl-]0 caused marked loss of these frequency dependency in phase 1 and this effect was more prominent with slow rate of stimulation. The slopes of phase 2 and phase 3 also changed with varying frequency of stimulations but these changes were not affected much by chloride removal. Chloride conductance at the peak of the positive dynamic current increased linearly with membrane voltages from -20mV up to +20mV. Above this voltage, the conductance reached a plateau. A steady-state current voltage relationship was not influenced much by the chloride removal except slight decrease (31%) in membrane conductance near the resting membrane potential. The increase in frequency of pulses produced marked decrease in the positive dynamic current in the voltage clamp experiments. These results suggest that the positive dynamic current mainly contribute to the electrogenesis of phase 1 in Purkinje action potentials.View full abstractDownload PDF (7330K) -
Yuji ISHIYAMA, Hideyo YABU, Eisaku MIYAZAKI1975 Volume 25 Issue 6 Pages 719-732
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSThe effects of neuraminidase and phospholipase C on the contractility and the Ca++ -binding of guinea pig taenia coli were investigated. Potassium contracture or histamine-induced contracture of taenia coli was inhibited by treatment with neuraminidase, though acetylcholineinduced contracture was not. Treatment with phospholipase C markedly inhibited the contracture induced by isotonic potassium, histamine or acetylcholine. By treatment with neuraminidase for 4hr, about 40 μmol/100mg wet wt of sialic acid was released from taenia coli. This corresponded to two-fifths of total content of sialic acid. By treatment with phospholipase C for 2hr, a similar amount of sialic acid to that produced by neuraminidase treatment was released. The Scatchard plot of Ca++-binding was a biphasic pattern indicating the presence of two types of the Ca++-binding site with different affinity constants. Neuraminidase produced a 57% decrease in the amount of bound Ca++. The Scatchard plot of Ca++-binding changed to a monophasic pattern indicating the disappearance of the low affinity Ca++-binding site. Phospholipase C caused a 59% decrease of bound Ca++. The Scatchard plot also indicated the disappearance of the low affinity Ca++-binding site. From these results, we speculated that sialic acid residue of surface membrane of the muscle cell was first site in the Ca++-influx mechanism.View full abstractDownload PDF (1295K) -
Kiyoshi MORIYA, Hiroshi MAEKUBO, Kenichi HONMA, Shinji ITOH1975 Volume 25 Issue 6 Pages 733-746
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSEffects of norepinephrine infusion on rectal temperature, plasma free fatty acids (FFA) concentration and its turnover rate were studied in rats treated chronically with norepinephrine, thyroxine, or both. Chronic treatments with these hormones resulted in greater increases in rectal temperature and FFA turnover rate in response to norepinephrine as compared with the alterations in controls. Norepinephrine-induced elevation of FFA concentration was smaller in norepinephrine-treated and norepinephrine plus thyroxine-treated rats than in controls, and in thyroxine-treated rats the elevation was similar to that of controls. The regression coefficient of FFA concentration of its turnover rate was greater in all the treated groups than in controls although positive correlations were observed among both variables in the former and the latter. From the results it was inferred that the greater increase in removal of plasma FFA was produced by norepinephrine in parallel with the greater increase in rectal temperature by norepinephrine in rats treated with norepinephrine or thyroxine than in the controls. The effects of norepinephrine infusion were also studied in surgically thyroidectomized rats. In thyroidectomized rats adapted to warm or cold, the smaller increases in rectal temperature and in the turnover rate of plasma FFA were induced by norepinephrine as compared with the changes in intact rats. The alterations in FFA concentration produced by norepinephrine were less in warm-adapted thyroidectomized rats and rather greater in cold-acclimated thyroidectomized rats than in respective controls.View full abstractDownload PDF (1367K) -
Masa TAKAUJI, Nobuaki TAKAHASHI, Torao NAGAI1975 Volume 25 Issue 6 Pages 747-758
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSThe effect of dantrolene sodium, 1-[5-(p-nitrophenyl) furfurylideneamino] hydantoin sodium hydrate, on electrical and mechanical response in frog skeletal muscles (whole muscles or single fibers) and on the biochemical properties of contractile proteins and fragmented sarcoplasmic reticulum isolated from frog or rabbit skeletal muscle was investigated. The peak tensions of twitch, tetanus and potassium contracture were significantly inhibited by dantrolene, without affecting the magnitude of resting potential, the amplitude and duration of action potential and the negative afterpotential. On the other hand, ATPinduced shortening of glycerol-extracted rabbit psoas muscle fibers, ATPase activity of frog myofibrils and Ca release induced by caffeine, Ca uptake and ATPase activity of fragmented sarcoplasmic reticulum of frog or rabbit muscle were not affected by dantrolene. Caffeine contracture was partially inhibited by dantrolene and was almost unchanged by it in potassium-depolarized muscle fiber. Nitrate ions and low concentration of caffeine rapidly recovered the twitch inhibition induced by dantrolene. These results suggested that dantrolene acts on the membrane of transverse tubules and possibly the triadic junction and that it inhibits the inward movement of Ca and subsequently decreases the release of activator Ca from sarcoplasmic reticulum.View full abstractDownload PDF (5528K) -
Hikaru SUZUKI, Hirosi KURIYAMA1975 Volume 25 Issue 6 Pages 759-773
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSThe membrane potential of the electrically quiescent circular muscle fibre is higher than that of the spontaneously active longitudinal muscle fibre. The length constant of circular muscle fibres is longer than that of the longitudinal muscle. The electrical activity of the longitudinal muscle membrane is enhanced by caffeine and PGE1 is suppressed for the circular muscle. Isotonic K Krebs solution generates a large tonic response of the contracture of longitudinal muscle tissue, but in circular muscle it is small. Following an inward current pulse, a large rebound contraction of the circular muscle was generated during K-induced contracture but it was small in the longitudinal muscle tissue. Caffeine suppressed the K-induced contracture of both tissues but enhanced the rebound contraction of the circular muscle. Verapamil and lanthanum suppressed the mechanical responses of both muscle tissues but rebound contraction evoked in isotonic K Krebs solution was of longer duration in circular muscle tissue than in longitudinal muscle tissues. It is postulated that both muscle tissues possess different electrical and mechanical properties, and that these differences are not caused by nervous activity.View full abstractDownload PDF (1586K) -
Satoshi KURIHARA1975 Volume 25 Issue 6 Pages 775-788
Published: 1975
Released on J-STAGE: June 07, 2011
JOURNAL FREE ACCESSProcaine (1-15mM) enhanced the spontaneous contractions of the urinary bladder smooth muscle. When a low concentration of procaine was added to normal Krebs solution, spontaneous rhythmic contractions were enhanced. On increasing the concentration of procaine, a rise in tone (resting tension) of the preparation was observed and gradually decreased with time. The action of procaine of enhancing spontaneous contraction was observed in Na-deficient (sucrose substitution) and Na-free (Tris substitution) Krebs solutions. Tetrodotoxin (3×10-7g/ml) did not inhibit the effect of procaine on mechanical response. In normal Krebs solution, procaine depolarized the membrane and increased spike frequency. The peak potential of the spike increased at 1mM of procaine, but was suppressed at concentrations of more than 5mM. After-hyperpolarization of the spike was diminished by procaine and spike duration was prolonged. The maximum rate of rise of the spike was increased immediately after application of 1mM of procaine, but decreased with time. The maximum rate of fall of the spike was markedly decreased by procaine. Relative membrane resistance was increased by the application of procaine. From these results it is suggested that procaine mainly reduces K conductance and causes depolarization, and that enhanced spontaneous contractions are caused by depolarization and increased spike activity.View full abstractDownload PDF (8133K)
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