Electrophysiological response of honey bee labial palp contact chemoreceptors to sugars and electrolytes

ABSTRACT. The sensilla chaetica on segments II, III and IV of honey-bee labial palps were investigated electrophysiologically. The responses (spikes/s) correlated with the log of the concentrations of sucrose, glucose, fructose, NaCl, KCl and LiCl, but not with CaCl₂ or MgCl₂, which gave inconsistent responses. The firing rates were higher and thresholds lower to the sugars than to the electrolytes. The sensitivity of the segments fell in the order: III > II > IV for most of the stimulants, which elicited responses in the order: sucrose > glucose = fructose' KCl > LiCl > NaCl. The sensilla adapted logarithmically with time. No synergism of response was noted when mixed-sugar solutions were applied, but inhibition of response was seen when glucose–sucrose, fructose–sucrose, and glucose–fructose–sucrose mixtures were applied. None of the sensilla tested responded to water.     

Electrophysiological responses of galeal contact chemoreceptors of Apis mellifera to selected sugars and electrolytes

Using conventional electrophysiological methods, the galeal sensilla chaetica of the honey bee, Apis mellifera, responded linearly to the log of solute concentrations of sucrose, glucose, fructose, NaCl, KCl, and LiCl but not to CaCl₂ or MgCl₂, which failed to give consistent responses. These sensillae had much higher firing rates for sugar than salt solutions; their relative responses to lower concentrations being NaCl < KCl < LiCl ? fructose < glucose ? sucrose. At higher concentrations NaCl < LiCl < KCl ? glucose < fructose ? sucrose. Four different spike types were seen. The first type had the highest amplitude and resulted from sugar stimulation. The second type had a lower height and occurred in the first 30 sec of salt stimulation. A third type with the lowest height appeared with those of the second type after prolonged stimulation with KCl. A fourth type with a high amplitude resulted from mechanical stimulation. The sensilla adapted to sugar solutions linearly to the logarithm of time and non-linearly to the log of salt concentrations. Glucose-fructose mixed-sugar solution effected synergism of response while sucrose solutions caused inhibition when mixed with glucose and/or fructose. Responses of the sensilla to mechanical stimulation showed phasic-tonic characteristics. None of the sensilla tested responded to water.     

Electric birefringence of dilute agarose solutions

The technique of transient electric birefringence was used to investigate the orientation of agarose solutions in pulsed electric fields. If the agarose was dissolved in deionized water, the sign of the birefringence was positive when the electric field was small, indicating that the agarose molecules were orienting parallel to the electric field lines. The decay of the birefringence was rapid, consistent with the orientation of individual agarose helices. The amplitude of the birefringence, but not the birefringence decay times, increased as the agarose solution aged, suggesting that the helices formed slowly from the sol state. Increasing the amplitude or duration of the pulsed electric field caused additional negative, and then positive, birefringence signals to appear, characterized by much slower rise and decay times, consistent with the formation of aggregates. The slowest decay times ranged from 7.5-9.0 s, suggesting that the aggregates were several microns in size. When agarose was dissolved in dilute Tris buffer instead of deionized water, the fast positive birefringence signal was not observed, suggesting that individual helices were not present in solutions containing dilute buffer.     

Infantile diarrhea; tolerance to solutions of electrolytes by mouth

Since Darrow's recommendation of electrolyte administration by mouth to infants with diarrhea, the constituting of a palatable liquid has been in the minds of all persons concerned with the treatment of diarrhea. Owing to the frequent association of gastric distress with oral administration of electrolyte solution, presumably because of increased osmolarity, a study was made at Kern County General Hospital to determine what osmolarity of solution was tolerated by most infants. For this purpose a commercially prepared oral electrolyte solution was used. When this new solution was given undiluted-that is, at an osmolarity of 20 times that of physiologic solution-only one of 29 patients, who were acutely ill and dehydrated, refused it or vomited it, probably due to irritation of the gastric mucosa. However, at a dilution of 1:3 with 5 per cent glucose and an osmolarity of six times physiological, only one of the 29 infants vomited and two others occasionally refused it. The length of hospital stay was not shortened by the substitution of the commercial preparation in either dilution. However, since the babies readily drank this electrolyte solution, it was possible to stop parenteral administration of electrolytes once fluid replacement had been carried out when the patient was first admitted.     

Convection-free boundary sedimentation of dilute protein solutions

Use of the density gradient sedimentation velocity technique appears to be essential for the accurate determination of the mean sedimentation coefficients of dilute protein solutions. When performed on an analytical ultracentrifuge equipped with a photoelectric-scanning-absorption optical system, the density gradient sedimentation velocity technique has been shown to be particularly useful in studying the subunit association-dissociation equilibria of multisubunit enzyme systems. The time factor has been shown to be a major advantage of the density gradient sedimentation velocity technique, as opposed to the sedimentation equilibrium technique, in studying the subunit association-dissociation equilibria of multisubunit enzymes such as rabbit muscle apo-glyceraldehyde-3-phosphate dehydrogenase, which is very unstable in dilute solution.     

Protein-protein association in polymer solutions: from dilute to semidilute to concentrated

In a typical cell, proteins function in the crowded cytoplasmic environment where 30% of the space is occupied by macromolecules of varying size and nature. This environment may be simulated in vitro using synthetic polymers. Here, we followed the association and diffusion rates of TEM1-beta-lactamase (TEM) and the beta-lactamase inhibitor protein (BLIP) in the presence of crowding agents of varying molecular mass, from monomers (ethylene glycol, glycerol, or sucrose) to polymeric agents such as different polyethylene glycols (PEGs, 0.2-8 kDa) and Ficoll. An inverse linear relation was found between translational diffusion of the proteins and viscosity in all solutions tested, in accordance with the Stokes-Einstein (SE) relation. Conversely, no simple relation was found between either rotational diffusion rates or association rates (k(on)) and viscosity. To assess the translational diffusion-independent steps along the association pathway, we introduced a new factor, alpha, which corrects the relative change in k(on) by the relative change in solution viscosity, thus measuring the deviations of the association rates from SE behavior. We found that these deviations were related to the three regimes of polymer solutions: dilute, semidilute, and concentrated. In the dilute regime PEGs interfere with TEM-BLIP association by introducing a repulsive force due to solvophobic preferential hydration, which results in slower association than predicted by the SE relation. Crossing over from the dilute to the semidilute regime results in positive deviations from SE behavior, i.e., relatively faster association rates. These can be attributed to the depletion interaction, which results in an effective attraction between the two proteins, winning over the repulsive force. In the concentrated regime, PEGs again dramatically slow down the association between TEM and BLIP, an effect that does not depend on the physical dimensions of PEGs, but rather on their mass concentration. This is probably a manifestation of the monomer-like repulsive depletion effect known to occur in concentrated polymer solutions. As a transition from moderate to high crowding agent concentration can occur in the cellular milieu, this behavior may modulate protein association in vivo, thereby modulating biological function.     

Molecular simulation of adsorption from dilute solutions

Adsorption of biomolecules on surfaces is a perennial and general challenge relevant to many fields in biotechnology. A change of the Helmholtz free energy DeltaA takes place when a molecule becomes adsorbed out of a bulk solution. The purpose of our investigations is to explore routes for the calculation of DeltaA by molecular simulations. DeltaA can be obtained both by integration over the mean force on a molecule and via the local density. It turns out that the route via the potential of mean force prevails over the latter due to better consistency. In this work we present results for systems of 1-centre and 2-centre Lennard-Jones mixtures at a 9/3 Lennard-Jones wall.     

Transport of water from concentrated to dilute solutions in cells of Nitella

The transport of water from concentrated to dilute solutions which occurs in the kidney and in a variety of living cells presents a problem of fundamental importance. If the cell acts as an osmometer we may expect to bring about such transport by creating an inwardly directed osmotic drive which is higher in one part of the cell than in other regions of the same cell. The osmotic drive is defined as the difference between internal and external osmotic pressure. Experiments with Nitella show that this expectation is justified. If water is placed at one end of the cell (A) and 0.4 M sucrose with an osmotic pressure of 11.2 atmospheres at the other end (B) water enters at A, passes along inside the cell, and escapes at B leaving behind at B the solutes which cannot pass out through the protoplasm. Hence the internal osmotic pressure becomes much higher at B than at A. When 0.4 M sucrose at B is replaced by 0.3 M sucrose with an osmotic pressure of 8.1 atmospheres we find that water enters at B, passes along inside the cell, and escapes at A so that water is transported from a concentrated to a dilute solution although the difference in osmotic pressure of the 2 solutions is more than 8 atmospheres. The solution at B thus becomes more concentrated. It is evident that if metabolism produces a higher osmotic pressure and consequently a higher inwardly directed osmotic drive in one region of the cell as compared with other parts of the same cell water may be transferred from a concentrated to a dilute solution so that the former solution becomes still more concentrated.     

Concentration of dilute solutions of macromolecules by electrophoresis

An electrophoresis apparatus which is used for concentrating micrograms of macromolecules from solutions as large as 250 ml is described. The recoveries were greater than 91% with three different macromolecules tested (28 to 360 kDa). Solutions with volumes in the range of 35 ml were concentrated 70-fold in less than 90 min to a final volume of 0.5 ml. Larger volumes in the range of 250 ml were concentrated 227-fold in 16 h to a final volume of 1.1 ml. Sterile concentrates can be obtained if the apparatus is constructed under sterile conditions.     

Sensory structures at the surface of fish skin I. Putative chemoreceptors

Fish skin contains solitary epidermal sensory cells which, on evidence from their cytology, are believed to be chemosensory. The external appearance of the apical sensory processes of these cells, as seen by scanning electron microscopy, is shown in four species of ostariophysan teleosts, and is compared with the morphology of the pores of external taste buds. The apical processes of the gustatory cells are simple in form in all cases so far investigated in gnathostome fishes, but in some cases the solitary sensory cells have apical processes divided distally into a number of smaller processes. In the dipnoan fish Protopterus amphibius , external taste buds have simple blunt gustatory processes protruding through a cap of mucus that covers the taste bud pore. Solitary sensory cells in this species have a bulbous undivided apical process. In the lampreys, the 'end buds' have an apical morphology different from the taste bud pores of teleost fish. Lamprey epidermis has numerous solitary sensory cells each bearing a number of microvilli.     

Radiation-induced polymerization in dilute aqueous solutions of cyanides

It has been found that the addition polymerization of cyanides (HCN and NH₄CN) takes place in dilute, O₂-free irradiated aqueous solutions, in addition to the abundant formation of various smaller molecules. A polymer with a molecular mass of 16,000 amu was found. Its abundance increases with initial cyanide concentration and absorbed dose and can be up to 31% of the total amount of radiolytic products. HPLC data also indicate the presence of two more products at 22,000 amu and 10,000 amu, which are less abundant by one order of magnitude. The same molecular masses appear throughout the examined range of cyanide concentration (0.001–0.2 mol dm^–3) and absorbed dose (2–200 kGy). They remain also at large doses (up to 1250 kGy) after a complete destruction of cyanide.     

The solubility of fibrinogen in dilute salt solutions

Highly purified human fibrinogen was dialyzed versus eleven different sodium salts at ionic strengths of 0.005–0.3 and pH values of 4.5–8.0. After equilibration and centrifugation of the protein solutions, fibrinogen solubilities were determined spectrophotometrically and were analyzed as functions of pH, ionic strength, and specific anion. Bell-shaped curves are obtained when fibrinogen solubility is plotted as a function of pH. The solubility exhibits a minimum at a given pH and rises at acid and alkaline values. As the ionic strength is increased, the solubility curves shift toward more acid pH values. At constant pH values between 6 and 7, fibrinogen solubility increases with an increase in ionic strength. At constant pH values below pH 6, a decrease in solubility occurs as the ionic strength is increased. The isoionic pH of a saturated aqueous fibrinogen solution has been determined to be 6.25, meaning that fibrinogen in pure water behaves as a weak acid with a mean net charge of ?0.9. At pH values acid to 6.25, the anions solubilize fibrinogen in the following order of increasing efficacy: thiocyanate, perchlorate, sulfate, citrate, bromide, nitrate, phosphate, chloride, acetate, fluoride, and formate. This order is reversed at pH values alkaline to 6.25. Anion binding parameters calculated from the solubility data indicate that those anions which most effectively solubilize fibrinogen at alkaline pH and precipitate it at acid pH have the highest apparent binding affinities for the protein. Anions with less pronounced solubility effects have lower binding affinities.