Effects of aluminium and pH on calcium fluxes,and effects of cadmium and manganese on calcium and sodium fluxes in brown trout (Salmo trutta L.)

• 1.1. Simultaneous measurement of calcium fluxes in brown trout, at low external [Ca] (20 μ mol 1⁻¹), provided evidence of active uptake of Ca from the medium.
• 2.2. At pH 4.5, calcium influx was inhibited and efflux was stimulated.
• 3.3. Cd and Mn, but not Al, at concentrations within the ranges found in acid waters experiencing fish population decline, inhibited calcium influx. Efflux was unaffected.
• 4.4. Cd and Mn stimulated sodium influx and efflux.

     

Some observations on the behaviour of the sodium efflux in barnacle muscle fibres towards lithium ions

• 1.1. The behaviour of the Na efflux towards Li⁺ was studied using single barnacle muscle fibres as a preparation.
• 2.2. It is found that the Na efflux into Li⁺-ASW (artificial seawater) is reduced and that this effect is not fully reversed by returning back to Na⁺-ASW.
• 3.3. Preinjection of 100 mM-EGTA reduces the magnitude of the fall of the Na efflux into Li⁺-ASW.
• 4.4(a). The remaining Na efflux into Li⁺-ASW is further reduced by external application of 10⁻⁴ M-ouabain. (b) The remaining Na efflux in ouabain-poisoned fibres is reduced by replacing Na_e by Li⁺. However, some fibres show a rise rather than a fall.
• 5.5. Fibres loaded with NaCl (by injection) show a prompt and sustained stimulation of the Na efflux when Na_e is replaced by Li⁺. A similar but less pronounced response is often seen with ouabain-poisoned fibres.
• 6.6. Injection of LiCl (e.g. a 2 M-solution), causes a 20% fall in Na efflux. Subsequent replacement of Na_e by Li⁺ fails to bring about a fall in the remaining efflux.
• 7.7. Itis concluded that the Na efflux in these fibres consists of a Na-Na exchange diffusion component which is not mediated by the Na-K pump and that its operation is interrupted by injecting Li⁺. The relative size of this component is about one-fifth and not one-half of the Na efflux.

     

Taurine regulation of Ca2+ uptake and (Ca2+ + Mg2+)-ATPase in developing chick B-cells

• 1.1. The objective of the present study was to determine the effect of age and taurine on chick B cell calcium uptake and membrane (Ca²⁺ + Mg²⁺)-ATPase activity in 1–4-week-old chicks.
• 2.2. The calcium uptake rate decreased with age (P < 0.05) and was further decreased by taurine (P < 0.05).
• 3.3. (Ca²⁺ + Mg²⁺)-ATPase activity increased with age (P < 0.05) and was stimulated by taurine (P < 0.05).
• 4.4. The data demonstrate that the flux of calcium across the B-cell membrane changes during early post-hatch development, and that taurine regulates both the influx and efflux of calcium in chick B-cells.

     

Uptake and release of calcium ions by heavy sarcoplasmic reticulum fraction of normal and malignant hyperthermia-susceptible human skeletal muscle

• 1.1. Ca²⁺ uptake, Ca²⁺-dependent ATPase activity and halothane-induced Ca²⁺ release from the heavy sarcoplasmic reticulum fraction of muscle from malignant hyperthermia susceptible individuals are similar to those of normal human muscle.
• 2.2. Ca²⁺-induced Ca²⁺ release from the diseased muscle was increased by 13%.

     

Inhibitors of active Ca2+ uptake by fragments of the sarcoplasmic reticulum of lobster muscle

• 1.1. Vesicles from the sarcoplasmic reticulum of lobster muscle accumulate Ca²⁺ if supplied with ATP as an energy source. A search was undertaken for inhibitors of Ca²⁺ transport.
• 2.2. p-Hydroxymercuribenzoate can completely inhibit Ca²⁺ transport and ATP hydrolysis. 2–4 Dinitrophenol inhibits uptake but not hydrolysis.
• 3.3. Sr²⁺, Ba²⁺ and Zn²⁺ inhibit uptake, perhaps by competing with Ca²⁺ for a carrier.
• 4.4. The vesicles contain acetylcholinesterase. Anticholinesterases can reduce —but not abolish—Ca²⁺ uptake. Acetylcholine has no effect on the activity of the vesicles.
• 5.5. Ca²⁺ uptake is not affected by Mn²⁺, glutamate, pilocarpine, carnosine, caffeine, strophanthidin or tetraethylammonium.
• 6.6. K⁺ is needed for maximal activity of the uptake system but not for ATP hydrolysis. Apparently K⁺ enhances the coupling between the energy supply and the carrier mechanism.

     

The multiplicity of neurotransmitters and neurohormones controlling mytilus muscle

• 1.1. The effects of various biogenic amines on contractions of the ABRM of M. edulis in response to repetitive electrical stimulation, ACh and high K⁺ concentration were examined.
• 2.2. Octopamine, serotonin, dopamine, noradrenaline, tyramine and phenylethanolamine potentiated the contractions of ABRM. Octopamine was found to be the most potent. Histamine did not potentiate.
• 3.3. Phentolamine blocked the potentiating action of octopamine and noradrenaline and partially blocked dopamine, but it did not block serotonin. Phentolamine also blocked the potentiating after-effect of repetitive electrical stimulation on subsequent contractions. It is suggested that octopamine is a neurotransmitter or a local neurohormone which potentiates contraction of the ABRM.
• 4.4. Under certain conditions, high concentrations of dopamine and serotonin inhibited contractions in response to ACh and high K⁺ concentration. Thus, these amines have not only potentiating but also inhibitory action on contraction of the ABRM, in addition to relaxing catch.
• 5.5. It is suggested that a wide spectrum of substances participates in the physiological control of contractility in the ABRM.

     

Activation of gastric mucosal calcium channels by epidermal growth factor

• 1.1. Gastric mucosal calcium channel complex was isolated from the solubilized epithelial cell membranes by affinity chromatography on wheat germ agglutinin.
• 2.2. The complex following labeling with [³H]PN200-110 was reconstituted into phosphatidylcholine vesicles which exhibited active ⁴⁵Ca²⁺ uptake into intravesicular space as evidenced by La³⁺ displacement and osmolarity measurements. The ⁴⁵Ca²⁺ uptake was independent of sodium and potassium gradients indicating the electroneutral nature of the process.
• 3.3. The gastric mucosal channels on epidermal growth factor binding in the presence of ATP responded by an increase in protein tyrosine phosphorylation of 55 and 170 kDa subunits of calcium channel.
• 4.4. The phosphorylated channels following reconstitution into vesicles displayed at 48% greater ⁴⁵Ca²⁺ uptake, thus indicating the tyrosine kinase involvement in EGF dependent activation of calcium channel.
• 5.5. The results point towards the importance of epidermal growth factor in the maintenance of gastric mucosal calcium homeostasis.

     

Modulation of gastric mucosal calcium channel activity by mucus glycoprotein

• 1.1. The effect of gastric mucus glycoprotein on the activity of calcium channel isolated from gastric epithelial cell membrane was investigated. The ⁴⁵Ca²⁺ uptake into the vesicle-reconstituted channels, while only moderately (14%) affected by the intact mucus glycoprotein, was found significantly inhibited (59%) by the acidic glycoprotein fraction. This effect was associated with the sialic acid and sulfate ester groups of the glycoprotein, as their removal caused a loss in the inhibition.
• 2.2. The channel complex in the presence of epidermal growth factor (EGF) and ATP responded by an increase in protein tyrosine phosphorylation of 55 and 170 kDa proteins, and the vesicles containing the phosphorylated channels showed a 50% increase in ⁴⁵Ca²⁺ uptake. The phosphorylation and the calcium uptake were susceptible to inhibition by a specific tyrosine kinase inhibitor, genistein.
• 3.3. The channel protein phosphorylation was inhibited by the acidic mucus glycoprotein, which also interfered with the binding of EGF to the channel protein. The inhibitory effect was dependent upon the presence of sulfate ester and sialic acid groups, as evidenced by the loss of the glycoprotein inhibitory capacity following their removal.
• 4.4. The results suggest that the acidic gastric mucus glycoproteins, by modulating the EGF-controlled calcium channel phosphorylation, play a major role in gastric mucosal calcium homeostasis.

     

Crayfish retinular cells: Influence of extracellular sodium and calcium upon receptor potential

• 1.1. In crayfish, light stimulation of the retinular cells induces a depolarizing receptor potential.
• 2.2. Experiments were designed to determine the role of Na⁺ and Ca²⁺ on receptor potential during dark And light states.
• 3.3. Depolarization depends on Na⁺ and Ca²⁺ availability to the retinular cell.
• 4.4. Repolarization velocity and response duration depend on extracellular Ca²⁺ availability.
• 5.5. Light adaptation increases receptor potential dependence on calcium and sodium ions.
• 6.6. We analyse these results with respect to other invertebrate photoreceptors.

     

Ca2+-dependent stimulation of muscle and liver phosphorylase kinase by heparin

• 1.1. Heparin stimulates the activity of nonactivated and activated skeletal muscle phosphorylase kinase in a Ca²⁺-dependent manner.
• 2.2. The stimulatory effect of heparin on the activity of nonactivated phosphorylase kinase is also expressed in the presence of calmodulin and glycogen. Heparin acted in synergism with glycogen.
• 3.3. Heparin increases the affinity of phosphorylase kinase to Ca²⁺ 5–12 fold depending upon the activation conditions.
• 4.4. Ca²⁺ influences the stimulation of liver phosphorylase kinase by heparin in a similar way.

     

The action of the venom of Philanthus triangulum F. on an insect visceral muscle

• 1.1. Low concentrations (0.05−0.38 BU/ml) of a crude venom extract from P. triangulum F. potentiate nerve-evoked contractions of the locust hindgut, possibly due to contamination of the venom preparation with proctolin.
• 2.2. Higher venom concentrations inhibit nerve-evoked contractions to a dose-independent plateau level.
• 3.3. The venom has no effect on responses to bath-applied proctolin, but responses to bath-applied L-glutamate are inhibited.
• 4.4. Spontaneous contractions are unaffected by the venom.
• 5.5. It is concluded that the plateau contractions are the result of excitation by non-glutamatergic transmission, and are possibly the result of proctolin release.

     

Myofibril and sarcoplasmic reticulum changes during muscle development: Activity vs inactivity

• 1.1. The purpose of this study was to determine whether biochemical changes of skeletal muscle that occur as a result of exercise in young rats persist into adulthood.
• 2.2. Littermates (10 days old) were assigned to a 3, 6 and 12 week control or training group. In addition, a rest-exercise group (R-E) and exercise-rest (E-R) group were included.
• 3.3. The rest-exercise and exercise-rest rats were maintained for the 12 weeks with the first 6 weeks being either rest or exercise and the condition reversed during the last 6 weeks of the experiment.
• 4.4. Myofibril ATPase activity of rat plantaris increased from the 10d to 12 week animals (P < 0.05). As anticipated, training resulted in a lowered activity at 6 and 12 weeks compared to controls.
• 5.5. The Ca²⁺ uptake and Ca²⁺-ATPase activity of the sarcoplasmic reticulum followed a similar pattern.
• 6.6. With regard to the exercise-rest rats, the myofibril and SR ATPase activities at 12 weeks were comparable to the 12 weeks control rats.
• 7.7. The rest-exercise group approximated the 12 week training group with regard to myofibril and SR ATPase activities (P > 0.05).
• 8.8. The results suggest that the training adaptations that occur during development of skeletal muscle return to normal, when training ceases in the adult rat.
• 9.9. Furthermore, animals that started to train prior to puberty do not have a greater capacity to adapt than animals which initiated training during adulthood.

     

The enzymatic properties of smooth muscle myosin B from dog colon

• 1.1. Smooth myosin B and myosin A were prepared from dog colon and their enzymatic properties were studied.
• 2.2. Colonic myosin B with two light chain corresponding to L₂ and L₃ in skeletal myosin showed much lower ATPase activities than rabbit skeletal myosin B.
• 3.3. The Mg²⁺-ATPase of myosin B was activated at high magnesium concentrations with the maximum activation between 10⁻³ and 10⁻²M and showed only a slight dependence on KCl concentration. On the other hand, Mg²⁺-ATPase activity of myosin A decreased with decreasing KCI concentration, suggesting the activation by actin of colonic myosin ATPase as much as skeletal myosin ATPase.
• 4.4. The pH dependence of Ca²⁺-ATPase showed a U-shaped curve although above pH 8.5 the activity was suppressed rapidly. The activity-ionic strength curve indicated that Ca²⁺- and ethylenediamine-tetraacetic acid (EDTA)-ATPase activities increased with increasing KCI concentration.
• 5.5. Mg²⁺-ATPase was fairly stable to urea treatment, whereas EDTA- and Ca²⁺-ATPase were activated by a low concentration of urea, followed by an inhibition.
• 6.6. These results were discussed as compared with those of skeletal myosin B.

     

Regulation of buccal mucosal calcium channel activity by salivary mucins

• 1.1. The effect salivary mucins on the activity of calcium channel isolated from buccal mucosal cell membranes was investigated. The uptake of ⁴⁵Ca²⁺while only moderately (15%) affected by the intact low and high molecular weight mucin forms, was significantly inhibited, by the acidic low and high molecular weight salivary mucins which evoked 64 and 60% inhibition, respectively.
• 2.2. The inhibitory effect of salivary mucins was associated with the sialic acid and sulfate ester groups of the carbohydrate chains, as the removal of either group caused partial loss in the glycoproteins inhibition, and the complete loss in the inhibitory effect occurred following desialylation and desulfation.
• 3.3. The channel in the presence of epidermal growth factor (EGF) and ATP responded by an increase in tyrosine phosphorylation of 55 and 170 kDa proteins, and the phosphorylated channels showed a 46% increase in ⁴⁵Ca²⁺ uptake. The phosphorylation and the calcium uptake were susceptible to inhibition by a specific tyrosine kinase inhibitor, genistein.
• 4.4. The binding of EGF to calcium channel receptor protein was inhibited by the low and high molecular weight acidic mucins, causing 41.2 and 36.1% reduction, respectively. This reduction in binding was dependent upon the presence of sulfate ester and sialic acid groups, as evidenced by the loss of the glycoproteins' inhibitory capacity following removal of these groups.
• 5.5. The results for the first time demonstrate that salivary mucins actively participate in the modulation of the EGF-controlled buccal mucosal calcium channel activity expression, a process of importance to the preservation of oral tissue integrity.

     

The exchange of radioactive cations by somatic and cardiac muscles of the crayfish

• 1.1. Intracellular concentrations of Na⁺, K⁺, Ca²⁺ and Mg²⁺ were measured in a somatic muscle and in the heart of the crayfish. The uptake and the efflux of Na²⁴, K⁴², Ca⁴⁵ and of Sr⁸⁹ were also measured.
• 2.2. The initial influx rates of the ions from van Harreveld's solution into resting somatic muscle (in μEq/g cell water/hr) are: K⁺ = 25; Na⁺ = 56; Ca²⁺ = 38. Similar figures were obtained for the heart muscle.
• 3.3. The calculated permeability constants (× 10⁸ cm/sec) are: P_K = 64; P_Na = 30 P_Ca = 10; P_Sr = 1·5.
• 4.4. The stimulation of the muscle fiber leads to an additional Ca²⁺ influx of about 2·8 pEq/cm² fiber surface. The additional Ca²⁺ uptake is sufficient to account for the change in potential on the membrane.
• 5.5. When muscles were immersed in Sr²⁺ solutions, no additional Sr⁸⁹ uptake was found with stimulation. However, there is a high resting Sr⁸⁹ uptake and the muscle in Sr²⁺ has a long refractory period, so a reasonable increase in Sr⁸⁹ uptake would not be detectable.
• 6.6. The results are discussed in relation to the divalent cation mechanism for generating action potentials and to the part played by Ca²⁺ in triggering contraction.

     

Comparative studies of sodium transport and its relation to hydrostatic pressure in deep and shallow water gammarid crustaceans from Lake Baikal

• 1.1. Freshwater gammarids from 900–1400 m depths lose Na at 1 atm, 4°C, while related shallow water gammarids are near neutral Na balance.
• 2.2. Na⁺ influx rates are similar at 1 atm, 4°C, for abyssal and shallow water gammarids of similar weight.
• 3.3. Na⁺ efflux is faster for abyssal gammarids than for comparable shallow water gammarids.
• 4.4. Compressing abyssal gammarids to 90–140 atm increases Na⁺ influx rates enough to restore neutral Na balance, while in shallow water crustaceans, compression decreases Na⁺ influx.
• 5.5. Na⁺ influx rates in Baikalian gammarids vary with the 0.55 power of weight.
• 6.6. The equation F_{ma × t} = 1.3 × W^0.55 μEq/hr/animal applies to freshwater crustaceans over the weight range from 0.03 to 35 g.

     

Modulation of the ATP induced [Ca2+]c increase in as-30D hepatoma cells

• 1.1. The regulation of the increase in the cytosolic calcium concentration ([Ca²⁺]c) induced by extracellular ATP in AS-30D hepatoma cells was studied.
• 2.2. Homologous desensitization involving the refilling of intracellular calcium pools and the participation of protein kinase C was found.
• 3.3. Isoproterenol, forskolin and dibutyril-cyclic AMP also induced an increase in [Ca²⁺]c.
• 4.4. Interestingly, synergism was found for isoproterenol or forskolin and ATP.
• 5.5. The results suggest that there are two pathways for mobilizing [Ca²⁺] in AS-30D hepatoma cells; one is activated by ATP receptors and the other by cyclic AMP.

     

Aluminium and calcium affect the perivitelline fluid in fish eggs

• 1.1. Microelectrodes have been used to measure K⁺ activities and electrical potential differences between the perivitelline fluid (pvf) of the eggs of pike (Esox lucius) and surrounding water in a range of pH, calcium and aluminium concentrations.
• 2.2. Potential differences between pvf and water are decreased by Ca²⁺ (10⁻³ M) while Al³⁺ (18 × 10⁻⁶ M) reverses the polarity of the potential difference.
• 3.3. K⁺ activities in the pvf of eggs in 10⁻⁴M KCl + 10⁻⁵M NaCl are decreased by Ca²⁺(10⁻³ M).
• 4.4. The results are discussed with reference to ion-exchange theory and chorion permeability.

     

Tetanus responses under rapid bath solution change: Electrotonic depolarization of transverse tubules may release Ca2+ from sarcoplasmic reticulum of Rana japonica skeletal muscle

• 1.1. Single skeletal muscle fibers were transferred from a normal Ringer solution to Na⁺ ion free solution, and vice versa, and tetanus responses were recorded immediately after the transfer.
• 2.2. Fractional tetanus tension recorded immediately after the displacement from the Na⁺ ion free solution to normal Ringer solution was dependent on fiber diameter.
• 3.3. Diffusion of Na⁺ ions along the transverse tubules was simulated [apparent diffusion constant was 3.11 × 10⁻⁶ (cm²/s)].
• 4.4. Our results suggest that the electrotonic spreading of membrane potential, caused by an action potential in the transverse tubules, could release Ca²⁺ ions from sarcoplasmic reticulum.

     

The effects of ryanodine,acetylcholine and epinephrine on electrical and mechanical activity in an insect heart

• 1.1. Ryanodine, an alkaloid used as an insecticide, has been shown to depress contraction while leaving excitation unaffected in mammalian hearts, an effect presumed to result from uncoupling of the transverse tubular system (TTS) from the sarcoplasmic reticulum (SR).
• 2.2. The heart of the adult moth Hyalophora cecropia, a tissue known to have septate junctions between the TTS and SR and a Ca²⁺ -spike generating sarcolemma was used to further test this hypothesis.
• 3.3. We first report the basic characteristics of the contractile response and demonstrate a negative force-frequency effect, a diminished calcium current (I_Ca²⁺) in the presence of acetylcholine and an enhanced I_Ca²⁺ with epinephrine.
• 4.4. Ryanodine 10⁻⁸M added to this preparation slowed the inherent rhythm (interval 0.6–4 sec), depolarized the cells by 10–14 mV, reduced action-potential amplitude (from 66 to 52 mV), prolonged the plateau (from 80 to 280 msec), and decreased dV/dt from 4 to 2.8 V/sec.
• 5.5. The magnitude of peak tension was not affected, but the time to peak tension was increased from 160 to 200 msec and the relaxation time was prolonged from 200 to 480 msec.
• 6.6. The refractory period was increased, thereby preventing the heart from following increased rates of pacing by externally applied stimuli.
• 7.7. We conclude that ryanodine interferes first with the sarcolemmal Ca²⁺-delivery system and then the SR calcium-sequestration system.