Spontaneous and propagated contractions in rat cardiac trabeculae

Sarcomere length measurement by microscopic and laser diffraction techniques in trabeculae of rat heart, superfused with Krebs-Henseleit solution at 21 degrees C, showed spontaneous local sarcomere shortening after electrically stimulated twitches. The contractions originated in a region of several hundred micrometers throughout the width of the muscle close to the end of the preparation that was damaged by dissection. The contractions propagated at a constant velocity along the trabeculae. The velocity of propagation increased from 0 to 10 mm/s in proportion to the number of stimuli (3-30) in a train of electrically evoked twitches at 2 Hz and at an external calcium ion concentration ([Ca++]o) of 1.5 mM. At a constant number of stimuli (n), the velocity of propagation increased from 0 to 15 mm/s with [Ca++]o increasing from 1 to 7 mM. In addition, increase of n and [Ca++]o led to an increase of the extent of local sarcomere shortening during the spontaneous contractions, and the occurrence of multiple contractions. Spontaneous contractions with much internal shortening and a high velocity of propagation frequently induced spontaneous synchronized contractions and eventually arrhythmias. Propagation of spontaneous contractions at low and variable velocity is consistent with the hypothesis that calcium leakage into damaged cells causes spontaneous calcium release from the overloaded sarcoplasmic reticulum in the damaged cells. This process propagates as a result of diffusion of calcium into adjacent cells, which triggers calcium release from their sarcoplasmic reticulum. We postulate that the propagation velocity depends on the intracellular calcium ion concentration, with increases with n and [Ca++]o.     

Spontaneous contractions of dispersed vascular muscle in cell culture.

Dispersed vascular muscle cells from chick omphalomesenteric vessels maintained in primary cell culture contracted spontaneously. Six methods which produced contracting isolated muscle cells are described and compared. The combination of dispersion method and culture conditions to produce contracting muscle cells was more critical for vascular than for heart muscle. These findings of continuing pacemaker function demonstrate that functional integrity of isolated vascular muscle cells is possible to maintain. Further indication of the full functional state of the isolated vascular muscle cells was demonstrated by the sensitivity to norepinephrine at a physiological concentration (0.1 muM). Spontaneous contraction frequencies were similar to the range found in situ, and spontanious or norepinephrine-induced contractions had time courses corresponding to intact vessel contractions. This is the first report that isolated vascular muscle cells in primary cell culture retain functional characteristics found in situ and are suitable for pharmacological characterization of individual muscle cells.     

Spontaneous contractions and nerve net activity in the sea anemone calliactis parasitica

Suction electrodes attached to tentacles of the sea anemone Calliactis parasitica record regular bursts of activity associated with the through‐conducting nerve net. Most bursts consist of 10–15 pulses at a frequency of 1 every 4 sec to 1 every 10 sec. The interval between bursts is usually 10–20 min. Regularity in pulse number and frequency in successive bursts suggests that the activity originates from a pacemaker. Bursts are always followed by slow contraction of endodermal longitudinal (parietal) muscles after a short delay, and endo‐dermal circular muscles after a long delay. A simple model for nervous pacemaker control of rhythmic contractions cannot be proposed as slow contractions can also occur in the absence of recorded nerve net activity.     

Spontaneous contractions in rat cardiac trabeculae. Trigger mechanism and propagation velocity

It has previously been observed that spontaneous contractions start in a region of damage of isolated right ventricular trabeculae of rat, propagate along the muscle, and induce triggered arrhythmias (Mulder, B.J.M., P.P. de Tombe, and H.E.D.J. ter Keurs. 1989. J. Gen. Physiol. 93:943-961). The present study was designed to analyze the mechanisms that lead to triggered propagated contractions (TPCs). TPCs were elicited in 29 trabeculae by stimulation with trains (2 Hz; 15-s intervals) at varied number of stimuli (n), lowered temperature (19-21 degrees C), and varied [Ca++]o (1.5-4 mM) in the superfusate. Length (SL) and shortening of sarcomeres in the muscle were measured at two sites using laser diffraction techniques; twitch force (Ft) was measured with a silicon strain gauge. Time between the last stimulus in the train and the onset of sarcomere shortening due to a TPC at a site close to the damaged end region (latency) and propagation velocity of the contraction (Vprop) were correlated with Ft. For 10 trabeculae, TPCs were calculated to start in the end region itself 586 +/- 28 ms (mean +/- 1 SEM) after the last stimulus of a train (n = 15; [Ca++]o: 1.5 mM), i.e., at the end of or after the rapid release of the damaged end during twitch relaxation. When Ft was increased by increasing either SL prior to stimulation or the afterload during twitches, methods that do not affect intracellular calcium levels, latency decreased, but Vprop remained constant. No TPC occurred when Ft was less than 20% of maximal Ft. Both increasing [Ca++]o and n increased Ft to a maximum, increased Vprop progressively (maximum Vprop, 17 mm/s), but decreased latency. These observations suggest that initiation of TPCs depends on the force developed by the preceding twitch, and therefore on the degree of stretch and subsequent rapid release of damaged areas in the myocardium, while Vprop along the trabeculae is determined by intracellular calcium concentration.     

Effects of glucocorticoids on contractions and electric activity of lymphatic vessels

Glucocorticoids were found to affect the membranes of lymphatic vessels' myocytes. Mechanisms of this action were studied.     

Ureogenesis in elasmobranch fishes

• 1.(1) The following reactions have been directly demonstrated in extracts from acetone powders prepared from the livers of several species of elasmobranch fishes:(i) carbamyl phosphate+ornithine → citrulline(ii) citrulline+aspartate → urea.
• 2.(2) There is strong circumstantial evidence that reaction (ii) proceeds by way of argininosuccinate and arginine.
• 3.(3) Attempts to demonstrate a synthesis of carbamyl phosphate were unsuccessful.
     

Spontaneous and neurally evoked contractions of visceral muscles in the oviduct of Locusta migratoria

The oviducts of Locusta migratoria are innervated by a pair of nerves which arise from, the seventh abdominal ganglion. A distinctive network of striated muscle fibres occurs in the oviducts. The lateral oviducts and common oviduct consist of an inner circular layer of muscle and an outer longitudinal layer of muscle. At the junction of the lateral and common oviduct an additional thin longitudinal layer is found adjacent to the basement epithelium. The oviducts contracted spontaneously when isolated from the central nervous system. These myogenic contractions took the form of peristaltic contractions in the lateral oviduct, and intermittent phasic-like contractions of the posterior regions of the lateral oviduct and the common oviduct. These phasic-like contractions were associated with individual complex potentials recorded extracellularly from the muscle fibres. In locusts that had been interrupted in the process of egg laying, there were large-amplitude action potentials, firing in a bursting pattern, in the oviducal nerves. These large action potentials were absent in locusts that had not been egg-laying. These action potentials were associated with both bioelectric potentials and mechanical events in the posterior region of the lateral oviduct and the common oviduct. Electrical stimulation of the oviducal nerve mimicked the effects of spontaneous action potentials, resulting in the appearance of monophasic potentials and contractions. The contractions were graded and dependent upon both frequency and duration of stimulation. It is concluded that the oviducts of Locusta are both myogenic and neurogenic. The role of these contractions in oviposition is discussed.     

Gill function in an elasmobranch

Summary Highly efficient oxygen uptake in elasmobranchs, as indicated by frequent excess of over has previously been ascribed to the operation of multicapillary rather than counter-current gas exchange by the gills. Analysis of models shows that, at maximum efficiency, a multicapillary system cannot account for values of greater than . In Port Jackson sharks Heterodontus portusjacksoni) commonly exceeds , which indicates the operation of a functional counter-current at the respiratory surface. The anatomical basis of this counter-current is provided by the demonstration that a continuous flow of water passes between the secondary lamellae into septal canals and thence via the parabranchial cavities to the exterior.Queen Elizabeth II Fellow.     

Influence of osmolytes, thin filaments, and solubility state on elasmobranch phosphofructokinase in vitro

Skeletal muscle phosphofructokinase (PFK) purified from the thornback ray is rapidly inactivated by urea concentrations as low as 50 mM at pH values below 7.0. Urea-induced loss of PFK activity is not offset by trimethylamine-N-oxide. Protection against urea-inactivation in vivo, where urea concentration may approach 0.5 M, may be due to two effects. Filamentous (F) actin and muscle thin filaments moderately reduce the urea-induced loss of PFK activity. The binding of PFK to F-actin and to thin filaments is shown by ultracentrifugation experiments. PFK activity in vivo also may be stabilized in this species by the formation of a particulate enzyme form which is totally resistant to inactivation by physiological concentrations of urea.     

Effect of amitraz on contractions of the guinea-pig ileum in vitro

• 1.1. The effect of the formamidine pesticide amitraz on the motility of isolated pieces of guinea-pig ileum was studied.
• 2.2. Contractions of the ileum stimulated by histamine and the histamine H₁ agonists 2-methylhistamine and 2-pyridylethylamine were inhibited by amitraz at a concentration of 1 μg/ml.
• 3.3. Amitraz did not inhibit contractions stimulated by acetylcholine, methacholine or dimethylphenylpiperazinium.

4. When pieces of intestine were left exposed to amitraz for several minutes they began to contract. These contractions appeared as rhythmic contractions and their strength did not appear to be increased by increasing the concentration of amitraz.5. It is concluded that amitraz inhibits the action of histamine H₁ agonists on the guinea-pig ileum and itself has a weak agonist effect.     

Regulation of egg laying and in vitro oviductal contractions in Gryllus bimaculatus

Oviductal contractions and the control of oviposition were investigated in vivo and in vitro in Gryllus bimaculatus females. In vivo experiments showed that oviposition is controlled nervously by both the brain and the last abdominal ganglion, and that one or more neurohormones cause ovipositor movements and abdominal contractions. In vitro, the assay of nerve ganglia and corpora cardiaca extracts on the isolated oviduct showed that they markedly increase the frequency of oviductal contractions. However, the action of thoracic ganglia extracts varies according to a circadian cycle. This observation, combined with the finding that the effects of the corpora cardiaca differ from those of the brain, suggests that each of these organs contains distinct neurohormones. None of the neurotransmitters tested was as potent as brain or ganglia extracts, although octopamine, l-glutamate and proctolin do stimulate oviductal contractions at low concentrations.     

Predation on elasmobranch eggs

Synopsis Predation on large, energy rich eggs is common in terrestrial and freshwater communities with the eggs of amphibians, reptiles and birds figuring as prominant prey. We might predict that predation on large eggs would also be widespread in marine communities. However, little information is available to test this prediction. We present new evidence for such predation on elasmobranch eggs based on examination of capsules held in museum collections, those collected from beaches, long-term incubations of caged egg capsules, and SCUBA observation. The principal egg predators appear to be gastropods, though vertebrates contribute to mortality of embryonic elasmobranchs. As yet we can only speculate about the effects of egg predation for populations of oviparous elasmobranchs, or about the direct and indirect consequences predation upon their energy-rich eggs may have for marine communities.     

Ventricle morphology in pelagic elasmobranch fishes

Ventricle weights of the warm-bodied great white shark, Atlantic shortfin mako, and the common thresher shark (the latter presumed to be warm-bodied) are similar to those of ectothermic blue sharks, sandbar sharks, dusky sharks, tiger sharks and scalloped hammerhead sharks. Ventricle muscularity, as estimated by the ratio of cortical to spongy layer thickness, is almost twice as great in the former three species than in the latter elasmobranchs. Measurements of ventricular volumes suggest that the ventricles of the great white, Atlantic shortfin mako and common thresher sharks are better adapted to respond to demands for increases in cardiac output via increased heartbeat frequency in comparison with ectothermic species of shark.     

Formation of prostanoids in human umbilical vessels perfused in vitro

Four major prostanoids (6-keto-PGF1 alpha, PGE2, PGF2 alpha and TXB2) were measured by specific radioimmunoassays in the outputs from human umbilical vessels perfused in vitro. As evaluated by scanning electron microscopy (SEM) only few blood platelets were attached to the vessel wall. After an initial flush with decreasing concentrations of all four prostanoids, a stable stage was reached, lasting for 4-5 hours. During this stage the production could be inhibited by indomethacin and only slightly stimulated with arachidonic acid. The TXA2 synthetase inhibitor UK 38485 depressed the TXB2 production, while only slightly affecting the other three prostanoids at very high concentrations. The arteries produced relatively more 6-keto-PGF1 alpha than did the vein.