Suechika Suzuki

Evidence for extracellular localization of activator calcium in dog coronary artery smooth muscle as studied by the pyroantimonate method

SummaryCorrelated physiological and electron-microscopic studies were made on the source of calcium activating the contractile system (activator calcium) in dog coronary artery smooth muscle fibers. The magnitude of contracture tension induced by 100 mM K+ was dependent on external Ca2+ concentration and reduced or eliminated by factors known to reduce the Ca2+ spike or ca2+ influx. Little or no mechanical response was elicited by treatments known to cause release of intracellularly stored calcium. These results indicated that the contractile system is mainly activated by the inward movement of extracellular calcium. In accordance with the physiological experiments, electron-opaque pyroantimonate precipitate containing calcium was found in the lumina of caveolae, but not in any intracellular structures close to the plasma membrane, when the relaxed fibers were fixed in a 1% osmium tetroxide solution containing 2% potassium pyroantimonate. If the contracted fibers were fixed in the same solution, the pyroantimonate precipitate was diffusely distributed in the myoplasm in the form of numerous particles, while the precipitate in the caveolar lumina was scarcely seen. These findings are discussed in connection with the regulation of intracellular Ca2+ concentration in dog coronary artery smooth muscle.

The nature of potassium- and acetylcholine-induced contractures in the anterior byssal retractor muscle of Mytilus edulis

Abstract 1. In the anterior byssal retractor muscle of Mytilus edulis , the relation between extent of recovery and [K] 0 was a mirror image of that between tension and [K] 0 . 2. High [Ca] 0 shifted the tension vs [K] 0 curve to the left, and the tension vs ACh concentration curve to the right. 3. Caffeine in subthreshold concentrations had no effect on K- and ACh-contractures. 4. Low temperature reduced the maximal K- and ACh-contractures without changing mechanical threshold. 5. These results are consistent with the view that potassium- and ACh-contractures are mainly due to inward movement of extracellular Ca and release of intracellularly stored Ca respectively.

Intracellular calcium translocation during the contraction–relaxation cycle in scorpionfish swimbladder muscle

SUMMARY To examine intracellular Ca2+ translocation during the contraction–relaxation cycle in vertebrate striated muscle, electron probe X-ray microanalysis was performed on the swimbladder muscle (SBM) fibres of a scorpionfish Sebastiscus marmoratus. The SBM fibres were rapidly frozen at rest, during contraction and at various times after the onset of relaxation. Changes in calcium distribution in the components of the sarcoplasmic reticulum (SR) were examined on the SBM fibre cryosections. In resting fibres, the calcium concentration was highest around the boundary between the A and I bands (A–I boundary), where the terminal cisternae (TC) were located. In contracting fibres, the calcium concentration decreased around the A–I boundary, while it increased in all other regions of the sarcomere, indicating Ca2+ release from the TC into the myoplasm. During relaxation, the calcium concentration first increased around the regions, where the fenestrated collars (FC) and the longitudinal tubules (LT) were located, and then gradually returned to the levels seen in resting fibres. These results support the view that, after the onset of relaxation in the SBM fibres, Ca2+ in the myoplasm is first taken up by the FC and the LT, and then gradually returns to the TC.

Regulatory mechanism of contraction in the proboscis retractor muscle of a sipunculid worm, Phascolosoma scolops

SummaryRegulatory mechanism of contraction in the proboscis retractor muscle of Phascolosoma scolops was studied by physiological measurements and cytochemical electron microscopy. The magnitude of K+-contracture was dependent on external Ca2+ concentration and the contracture disappeared in Ca2+-free solution. The K+-contracture was suppressed by application of procaine and Mn2+. Caffeine induced contracture even when external Ca2+ was absent. Ultrastructural observations of the retractor muscle cells showed the presence of a large number of vesicles (subsarcolemmal vesicles), corresponding to the sarcoplasmic reticulum in vertebrate skeletal muscle, underneath the plasma membrane. For the cytochemical electron microscopy, the muscle fibers were fixed with 1% OsO4 solution containing 2% K-pyroantimonate. In the relaxed fibers, pyroantimonate precipitates were localized along the inner surface of plasma membrane and in the subsarcolemmal vesicles. In the contracting fibers, the precipitates were uniformly distributed in the myoplasm. The X-ray microanalysis revealed that the precipitates contained Ca. These results suggest that the contractile system is activated by the influx of extracellular Ca2+ as well as by the release of Ca2+ from the intracellular structures such as the inner surface of the plasma membrane and subsarcolemmal vesicles.

Rigor-Force Producing Cross-Bridges in Skeletal Muscle Fibers Activated by a Substoichiometric Amount of ATP

Isometric skinned muscle fibers were activated by the photogeneration of a substoichiometric amount of ATP and their cross-bridge configurations examined during the development of the rigor force by x-ray diffraction and electron microscopy. By the photogeneration of approximately 100 microM ATP, approximately 2/3 of the concentration of the myosin heads in a muscle fiber, muscle fibers originally in the rigor state showed a transient drop of the force and then produced a long-lasting rigor force (approximately 50% of the maximal active force), which gradually recovered to the original force level with a time constant of approximately 4 s. Associated with the photoactivation, muscle fibers revealed small but distinct changes in the equatorial x-ray diffraction that run ahead of the development of force. After reaching a plateau of force, long-lasting intensity changes in the x-ray diffraction pattern developed in parallel with the force decline. Two-dimensional x-ray diffraction patterns and electron micrographs of the sectioned muscle fibers taken during the period of 1-1.9 s after the photoactivation were basically similar to those from rigor preparations but also contained features characteristic of fully activated fibers. In photoactivated muscle fibers, some cross-bridges bound photogenerated ATP and underwent an ATP hydrolysis cycle whereas a significant population of the cross-bridges remained attached to the thin actin filaments with no available ATP to bind. Analysis of the results obtained indicates that, during the ATP hydrolysis reaction, the cross-bridges detached from actin filaments and reattached either to the same original actin monomers or to neighboring actin monomers. The latter cross-bridges contribute to produce the rigor force by interacting with the actin filaments, first producing the active force and then being locked in a noncycling state(s), transforming their configuration on the actin filaments to stably sustain the produced force as a passive rigor force.

Frequent episodes of acute renal failure and a complication of Fanconi's syndrome in a patient with paroxysmal nocturnal hemoglobinuria

A 41-year-old man with aplastic anemia and paroxysmal nocturnal hemoglobinuria complex presented with complaints of frequent episodes of acute renal failure associated with hemolytic attacks. In the last admission he suffered from severe renal dysfunction that required hemodialysis for 3 weeks. A renal biopsy sample showed normal appearing of glomeruli and a moderate degree of tubular atrophy, probably due to massive ferrous deposition which was confirmed by x-ray analysis. He was found to have Fanconis syndrome, with phosphaturia, uricosuria, acidic aminoaciduria, and excessive urinaryβ2-microglobulin excretion. This is a case in which paroxysmal nocturnal hemoglobinuria caused frequent episodes of acute renal failure and a coincident Fanconis syndrome.

Cross-Bridge Angle Distribution and Thin Filament Stiffness in Frog Skeletal Muscle Fibers as Studied by Quick-Freeze Deep-Etch Electron Microscopy

To give information about changes in orientation of myosin heads (cross-bridges) during contraction, mechanically skinned frog muscle fibers were rapidly frozen in various states, and cross-bridge angles were measured on the freeze-etch replicas. Histograms of cross-bridge angle distribution showed a peak around 90 degrees in relaxed, contracting and rigor states. The proportion of cross-bridges taking angles around 90 degrees decreased when rigor fibers were stretched or released before freezing. These results are explained by assuming the stretch-induced tilting of cross-bridges due to elastic recoil of the thin filaments in the I-band. As a matter of fact, the axial spacing of actin monomers in the thin filament increased with increasing rigor force before freezing. The stiffness times unit length of the thin filament was estimated to be about 1.8 x 10(4) pN.

The effect of ions and drugs on the initiation and conduction of peristaltic wave in the heart of Ciona intestinalis.

Abstract 1. The effect of ions and drugs on the initiation and the conduction of peristaltic wave was studied on the heart of a tunicate, Ciona intestinalis . 2. The conduction of peristaltic wave was blocked by the replacement of [Na] o by choline, but not by the addition of Mn ions (20 mM) or the removal of [Ca] o . 3. Procaine (1 mM) inhibited the pacemaker activity, but did not block the conduction of peristaltic wave. The heart-beat was not influenced by tetrodotoxin (10 −6 g/ml) or picrotoxin (10 −3 g/ml). 4. These results indicate that the action potential in the muscle cells is mainly associated with the regenerative increase in Na-permeability.