Effects of K+, Ba2+ and Ca2+ on the excitable membrane in Paramecium tetraurelia

• 1.1. The effects of Ba²⁺ and K⁺ ions on the membrane currents of Paramecium tetraurelia under a voltage clamp were investigated.
• 2.2. External Ba²⁺ suppresses the inward-going K-current and the Ca-induced K-outward current and changes the activation and inactivation kinetics of transient inward current through the Ca-channel.
• 3.3. K⁺ increases the Ca-induced K-conductances but little affects the leakage conductance.
• 4.4. The resting potentials by changing those ionic concentrations shift the voltage sensitivities of all voltage sensitive channels, simultaneously.
• 5.5. The competition between ions to the channel responses was discussed.

     

Relative contribution of two mechanisms to post-stimulus hyperpolarization in leech retzius cells

• 1.1. In Retzius cells of the horse leech, Haemopis sanguisuga, intensive firing is followed by prolonged post-stimulus hyperpolarization (PSH) mediated by an increase in K-conductance and activation of the electrogenic sodium pump.
• 2.2. The recovery of membrane potential during PSH can be described by a biexponential model from which the relative contribution of the early and the late component to the peak amplitude of PSH may be calculated.
• 3.3. The time course of the calculated early component coincides with the time course of changes that occur in input membrane resistance during PSH.
• 4.4. The relative contribution of the late component increases linearly with an increase in stimulus duration. The rate constants of the two phases did not change with changes in stimulus duration.
• 5.5. It was concluded that the proposed model is useful for the estimation of the relative contribution and kinetics of two PSH mediating mechanisms (K-conductance increase and activation of an electrogenic sodium pump) in different experimental conditions.

     

Potassium channels in growth cones of leech retzius cells

• 1.1. Potassium-selective channels were analysed in growth cones of cultured leech Retzius cells.
• 2.2. In the cell-attached mode and at physiological bath and pipette solution little channel activity was observed at resting membrane potential. The channel open probability (p_o) increased with cell depolarization, and the slope conductance of the single K⁺ channel current was about 60 pS.
• 3.3. With symmetrical high KCl solution on both sides of the excised membrane patch three K⁺ -selective channels could be discriminated. Two channels exhibited a linear current-voltage relation of about 18 pS and 106 pS, respectively.
• 4.4. The most frequently observed K⁺ channel showed a non-linear current-voltage relation and p_o increased with increasing free cytoplasmic Ca²⁺ and during cell hyperpolarization.

     

Uptake of inorganic ions from the maternal circulation during development of the embryo of a viviparous lizard,Sphenomorphus quoyii

• 1.1. Inorganic ion content of developing follicles and of whole eggs and separated embryos and yolk sacs of the viviparous lizard, Sphenomorphus quoyii has been measured.
• 2.2. There is a net increase in calcium, sodium and potassium in whole eggs during gestation. Magnesium and phosphorus content remains constant.
• 3.3. The additional ions are incorporated into the developing embryo.
• 4.4. Calcium content of the yolk is compared with that of the fowl and other species of reptile.

     

Calcium-dependent potassium conductance in the photoresponse of a nudibranch mollusk

• 1.1. The response to light of Hermissenda photoreceptors when recorded intracellularly without interference from synaptic and action potentials consisted of three phases: an early depolarization (ED) followed by hyperpolarization (dip) and subsequent depolarization (tail).
• 2.2. The ED and the dip were associated with increased membrane conductance while decreased membrane conductance was involved with the tail.
• 3.3. The dip reversal potential was − 82.1 ± 5.3 mV and its amplitude varied inversely with the log of [K⁺].
• 4.4. Perfusing with agents which block K⁺ current like 4AP, Quinine, Quinidine or injection of TEA eliminated the dip and its associated increased membrane conductance, thus further supporting the role of K⁺ conductance in producing the dip.
• 5.5. The dip was enhanced by increased [Ca²⁺]_o, reduced by decreased [Ca²⁺]_o and abolished together with its associated increased membrane conductance when perfused with either D600, Cd²⁺, Mg²⁺, Mn²⁺, or Co²⁺, which block transmembrane Ca²⁺ current.
• 6.6. The dip and its associated increased membrane conductance were abolished by intracellular injection of EGTA and enhanced by perfusion with Ruthenium red.
• 7.7. Intracellular injection of Ca²⁺ mimicked the dip: membrane conductance was increased and the cell hyperpolarized.
• 8.8. These results indicate that the increase in intracellular [Ca²⁺] is primarily responsible for the light-induced increase of K⁺ conductance during the dip. The possible source of the Ca²⁺ is, at least in part, extracellular due to activation of an inward Ca²⁺ current.

     

The pharmacology of insect visceral muscle

• 1.1. At least five sites-of-action must be considered in most visceral nerve-muscle preparations.
• 2.2. L-Glutamate is perhaps the excitatory neuromuscular transmitter in some organs of the viscera but not others. Proctolin is probably a neuromuscular transmitter in some organs of the viscera defined criteria for rapid chemical transmission.
• 3.3. Although 5-HT and certain catecholamines are present in insects and have a pronounced effect on visceral muscle no functional roles has been established for them.
• 4.4. Various peptides released from neuroendocrine organs probably regulate visceral muscle function. Moreover such hormonal actions seem to be mediated by cyclic AMP in some cases.
• 5.5. Recent developments in methods for detecting peptides and prospective transmitters have increased the possibility of rapid progress in insect nerve-muscle pharmacology.

     

Mechanism of long lasting synaptic inhibition of a silent neuron of Helix pomatia

• 1.1. Long lasting synaptic inhibitions (LLI) were recorded in the silent cells LPL1 and RPL1 of Helix pomatia.
• 2.2. During LLI the excitability of the cell was strongly reduced.
• 3.3. The membrane conductance changes during LLI were characterized using the voltage-clamp technique.
• 4.4. LLI in the silent cell LPL1 is mediated by a synaptically induced inhibition of the voltage-dependent inward Ca²⁺ -current.

     

Factors regulating the functioning of the in vitro perfused aglomerular kidney of the anglerfish,Lophius piscatorius L.

• 1.1. Kidneys of Lophius were perfused from the renal portal vein with a Ringer's solution.
• 2.2. Mammalian and piscine neurohypophysial hormones (in doses of 20–500 ng/kg body wt) did not affect the rate of urine production or the urinary concentration of inorganic ions.
• 3.3. The rate of urine production and the urinary concentration of magnesium and sodium ions varied with the concentration of magnesium in the perfusate.
• 4.4. The rate of urine production was positively correlated with urine magnesium concentration (r = 0.83 ± 0.04) and negatively correlated with that of sodium (r = −0.40).
• 5.5. The urinary concentration of sodium ions varied inversely with that of magnesium ions (r = −0.89).
• 6.6. Ouabain treatment (0.1–0.8 mM/l) reduced the rate of urine production by over 60% and altered, to varying extents, the pattern of electrolyte excretion. A simple model for the mode of formation of urine by the aglomerular kidney, based on the present results and other observations is suggested.

     

Lipid and carbohydrate metabolism of the intertidal crab Chasmagnathus granulata dana, 1851 (Crustacea: Decapoda) during emersion

• 1.1. Lipid, glucose and glycogen concentrations were measured in different tissues of the crab Chasmagnathus granulata during emersion.
• 2.2. After 6 hr of emersion no reduction in the total amount of carbohydrates was found to occur, suggesting that a general metabolic arrest was taking place.
• 3.3. A transitory increase in haemolymphatic glucose and lipid levels was observed. Possible causes are therefore discussed in relation to changes in the flux of substrates for energy production.
• 4.4. The mobilization of carbohydrates and lipids to the gills, observed only during summer, may be concerned with energy supplying for ionic regulation.

     

The digestive enzymes of the pacific brown shrimp Penaeus californiensis.: I—Properties of amylase activity in the digestive tract

• 1.1. Crude extract of the whole digestive tract from the brown shrimp (P. californiensis) was investigated for digestive amylase activity.
• 2.2. Considerable amylase activity was found at pH 6.5–8.0, with optimum pH at around 7.5.
• 3.3. Optimum temperature was found between 30–40°C, similar to amylases from other crustaceans.
• 4.4. Amylase activity was highly halotolerant, having 50% maximum activity at 3 M NaCl.
• 5.5. Maximum amylase activity was found at 0.01 M NaCl.
• 6.6. Amylase activity was partially inhibited by the divalent ions Hg²⁺, Zn²⁺, Cu²⁺ and Cr²⁺.
• 7.7. Mg²⁺ and Ca²⁺ ions seemed to enhance amylase activity.

     

Preliminary studies on the characteristics of phenylalanine and β-methyl-glucoside transport in the tench intestine in vitro

• 1.1. The unidirectional transepithelial fluxes of L-phenylalanine, β-methyl-D-glucoside and sodium ions across emusculated sheets of tench mid-intestine were determined in flux chambers.
• 2.2. No net sodium flux was detectable, but phenylalanine was preferentially transferred from the mucosal to the serosal fluid.
• 3.3. There was also a net movement of β-methyl-glucoside towards the serosal medium, but it was much smaller than that of phenylalanine.
• 4.4. This transport was accompanied by an accumulation of each substrate from the mucosal medium into the tissue to a similar level and against a concentration gradient.
• 5.5. The poor transfer of the monosaccharide into the serosal medium could therefore be attributed to a low permeability of the baso-lateral membrane of the enterocyte for this substance.
• 6.6. The influx of L-phenylalanine and of β-methyl-d-glucoside into the epithelial cells of tench midintestine was examined by incubating slices of emusculated intestine in radioactively-labelled solutions of the substrate for 2 min.
• 7.7. The steady-state uptake was assessed after similar incubations lasting 45 min.
• 8.8. Phenylalanine influx obeys the Michaelis-Menten equation with a K_m of 2.9 mM and is dependent on the presence of sodium ions in the incubation medium.
• 9.9. β-Methyl-glucoside influx reveals the same characteristics with a K_m of 2.0 mM but a considerably lower V_max; in addition, it is inhibited by galactose.
• 10.10. The influx of both substrates is reduced by harmaline, which also inhibits the uptake of radioactive sodium by this preparation.
• 11.11. The steady-state uptake of β-methyl-glucoside is also inhibited by ouabain and by 2.4-dinitrophenol.
• 12.12. These results suggest that the mechanisms for sodium-dependent influx of monosaccharides and neutral amino-acids in the tench intestine are similar to those found in mammalian tissues.
• 13.13. The principal difference appears to involve the release of monosaccharides across the baso-lateral membrane of the enterocyte.

     

Porphyrin biosynthesis in Rhodopseudomonas palustris—IX. PBG-deaminase. Kinetic studies

• 1.1. PBG-Deaminase obtained from Rp. palustris exhibited classical Michaelis-Menten kinetics in the absence or presence of different ions.
• 2.2. Detailed kinetic studies were carried out in the presence of ammonium, phosphate and magnesium ions.
• 3.3. It has been found that the different effects observed are dependent on both the substrate and the ion concentration.

     

Adenosine triphosphate as a determinant of magnesium levels in cytoplasm

• 1.1. Levels of free magnesium ion in various tissues are reviewed.
• 2.2. Total magnesium and ATP levels in different tissues are correlated, due to the presence of MgATP.
• 3.3. Relationships between pH and temperature in poikilotherms are such as to keep constant the amount of magnesium bound by ATP.
• 4.4. ATP hydrolysis in vivo generally tends to release magnesium ions, but conditions in some muscle may be such as to minimize this release.

     

Growth and haematological response of sturgeon hybrids Russian sturgeon (Acipenser guldenstadti brandt) × beluga (Huso huso L.) to protein and lipid contents in the diet

• 1.1. Fingerlings of intergenious hybrid Russian sturgeon (Acipenser guldenstadti) × beluga (Huso huso) weighing 22 g reared in water with salinity 18 ppt were fed nine diets differing in protein and fat content.
• 2.2. The increase of dietary protein content (from 45 to 52%) improved the fingerlings growth rate, food and protein conversion efficiencies. No effect of further protein content increase to 60% was observed.
• 3.3. The increase of dietary fat content from 10 to 20% positively influenced all growth results.
• 4.4. The muscular lipid content increased following the increase in dietary fat due to accumulation of triacylglycerols.
• 5.5. Distinctive leucopenia in neutrophils and leucophilia in lymphocytes following dietary protein and fat content increase were observed.
• 6.6. It was concluded that within the analysed range of values the increase of dietary protein and lipid content improved the physiological status of sturgeon hybrid fingerlings.

     

The effect of cortisol on stimulation of enzymatic activity and absorption of amino acids in the small intestine of adult hamsters

• 1.1. The s.c. administration of cortisol to hamsters (50 mg/kg body wt/day for 4 days) produces a significant increase in maltase sucrase, alkaline phosphatase and leucineaminopeptidase activity in intestinal mucosa.
• 2.2. Lactase activity is unaffected by cortisol.
• 3.3. Gamma-glutamyltranspeptidase activity increases slightly in females but remains unchanged in males.
• 4.4. Cortisol causes increase in proline and glycine absorption without changing the absorption of lysine.

     

Climatic adaptation in the energetics of heteromyid rodents

• 1.1. The temperature regulation and heat production of two heteromyid rodents, Heteromys anomalus and Dipodomys deserti, were studied.
• 2.2. Heteromys has a high basal rate and a high minimal thermal conductance: D. deserti has a low basal rate and a low conductance. Other heteromyids, all of which, like D. deserti, live in arid environments, also have low basal rates and low thermal conductances. The depression of metabolism and conductance is most pronounced in small pocket-mice (Perognathus).
• 3.3. Low basal rates are an alternative to the production of a concentrated urine as a means of reducing water turnover in mammals with low water intake. Thus. among kangaroo-rats, species that live in mesic microenvironments and feed upon foods of a high water content, such as D. microps, have higher relative basal rates than other species. Heteromys differs from other heteromyids by inhabiting tropical rainforests, where water conservation is of minimal importance. Low basal rates may also be an adaptation to seasonally variable mast crops.
• 4.4. In the maintenance of a temperature differential with the environment, low conductances compensate for low rates of metabolism, especially at small body sizes.
• 5.5. These data are interpreted to mean that phylogeny, independent of ecological relations, has little influence on the energetics of endotherms.

     

Characterization of the Melanoplus sanguinipes hemolymph after infection with Beauveria bassiana or wounding

• 1.1. The phenoloxidase activity, protein and carbohydrate levels were studied for 24 hr in the hemolymph of the migratory grasshopper, Melanoplus sanguinipes after artificial wounding of the insect cuticle or the injection of Beauveria bassiana conidia.
• 2.2. Injection or wounding induced a primary response and phenoloxidase activity was found to increase within 10–60 min. The values for phenoloxidase activity in viable B. bassiana-injected insects exhibited a secondary response, i.e., an increase 24 hr after injection.
• 3.3. In wounded insects and those injected with inactivated conidia, the phenoloxidase activity receded after the initial increase and remained at low levels.
• 4.4. Protein concentrations in the hemolymph increased immediately after infection and wounding and returned to basal levels during the course of the experiment.
• 5.5. Injection of viable B. bassiana resulted in a gradual increase in the protein concentrations between 12 and 24 hr.
• 6.6. There was no apparent change in the carbohydrate levels in either B. bassiana-infected or wounded insects.
• 7.7. These results are discussed in relation to their possible role(s) and interrelationships in the immune response to infection or wounding. Furthermore, we suggest that a “factor” is released after mechanical injury of the integument.

     

12-O-tetradecanoylphorbol-13-acetate enhances glycolysis in rat thymocytes

• 1.1. The potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induced a rapid increase in glycolysis in rat thymocytes.
• 2.2. The increase in the glycolytic flux was also reflected by elevated fructose 1,6-diphosphate levels.
• 3.3. TPA treatment did not result in an increase of hexokinase, phosphofructokinase or pyruvate kinase when measured in cell homogenates.
• 4.4. It is suggested that the early increase in glycolysis in TPA treated lymphocytes may result from TPA-mediated increase in glucose transport.