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.     

Peripheral and central interactions between sugar,water, and salt receptors of the blowfly, Phormia regina

The peripheral and central nervous interactions between the sugar, water, and salt receptors of the blowfly were investigated electrophysiologically by simultaneously recording from the labellar chemoreceptors and the extensor muscle of the haustellum. Simultaneous stimulation of two water receptors with 10 mM LiCl resulted in a motor response even though stimulating the same two sensilla separately with 10 mM LiCl did not. There was a linear decrease in the motor response to two sensilla stimulation as the salt concentration in the stimulating solution increased. Although stimulating two sensilla simultaneously with 200 mM NaCl gave no motor response, simultaneously stimulating two sensilla with 10 mM LiCl and a third with 200 mM NaCl gave a greater response than did two sensilla stimulation with 10 mM LiCl alone, indicating cross-channel summation between the water and salt receptors. Similarly, simultaneously stimulating one sensillum with 100 mM sucrose and another with 10 mM LiCl or 500 mM NaCl gave a larger response than did 100 mM sucrose stimulation alone. The cross-channel summation between the sugar and water receptors was not affected by feeding the flies water. A central excitatory state (CES) which previously had been demonstrated behaviourally was investigated. A stimulation of one sensillum with 10 mM LiCl which previously had been ineffective gave a motor response if proceeded by a stimulation with 1 M sucrose on another sensillum. The effect of the time interval between the sugar and water stimuli was tested, but for intervals of 100 msec to 4 sec no definite correlation was found. In addition, CES with respect to the sugar receptor was demonstrated. The motor response to stimulation of a single sensillum with 100 mM sucrose was enhanced by preceding it with 1 M sucrose stimulation of another sensillum. The motor response to stimulation of two water receptors with 10 mM LiCl was partially inhibited by simultaneously stimulating a third sensillum with 4 M NaCl. Inhibition was also seen when a single sensillum was stimulated with a mixture of 10 mM LiCl and 10 mM sucrose and an adjacent sensillum was simultaneously stimulated with 1 M NaCl. Behavioural experiments showing inhibition of CES by salt were confirmed. Interposing a salt stimulus of 4 M NaCl between the 1 M sucrose and 10 mM LiCl stimuli reduced but did not totally eliminate the motor response to 10 mM LiCl. The basis for peripheral control of the relative activities of the water and salt receptors is discussed. A model is proposed to account for all the receptor interactions in the central nervous system.     

The neural activities of the greater superficial petrosal nerve of the rat in response to chemical stimulation of the palate

A comparison of the integrated responses of the rat's greatersuperficial petrosal (GSP) and chorda tympani (CT) nerves toa number of taste stimuli was studied. The GSP nerve of therat was very responsive to the chemical stimulation of the oralcavity. Among the selected stimuli related to the four basictaste qualities, 0.5 M sucrose produced the greatest neuralresponse in the GSP nerve, whereas, 0.1 M NaCl produced thegreatest in the CT nerve. The GSP nerve integrated responseto 0.5 M sucrose solution was approximately three times as greatin magnitude as that to a 0.1 M NaCl solution. The neural responsemagnitude of the GSP and CT nerves were as follows: GSP nerve;0.5 M sucrose >0.02 M Na-saccharin >0.05 M citric acid>0.1 M NaCl > 0.01 M quinine-HCl. CT nerve; 0.1 M NaCl> 0.05 M citric acid > 0.02 M Na-saccharin > 0.01 Mquinine-HCl >0.5 M sucrose. The response magnitudes of theGSP nerve to 0.3 M chloride salt solutions were: LiCl > CaCl₂> NaCl > NH₄Cl > KCl, whereas the response magnitudesof the CT nerve to the above salts were: LiCl > NaCl >NH₄Cl > CaCl₂ > KCl. All 0.5 M solutions of the selectedsugars (sucrose, rhamnose, galactose, lactose, fructose, -methyl-D-glucoside,xylose, mannose, arabinose, maltose, sorbose and glucose) evokedneural responses in both GSP and CT nerves. The order of theresponse magnitudes of the GSP nerve to the selected sugarswas similar to that of the CT nerve but the absolute magnitudesof the GSP nerve were greater.     

The effects of amiloride on the labellar taste receptor cells of the fleshfly Boettcherisca peregrina

Amiloride is known to inhibit the taste response of vertebrates to salt by blocking the amiloride-sensitive sodium channel. In this study, we investigated electrophysiologically the effect of amiloride on the taste response of the fleshfly Boettcherisca peregrina. When 0.5 mM amiloride was included in taste solutions, the response of the salt receptor cell (salt response) to sodium chloride (NaCl) was not depressed but those of the sugar receptor cell (sugar responses) to sucrose, glucose, fructose, l-valine (l-Val) and l-phenylalanine (l-Phe) were strongly depressed. An inhibitory effect of amiloride on the concentration-response relationship for both sucrose and l-Phe was clearly revealed, but not at high concentrations of sucrose. After pretreatment of a chemosensory seta with 0.15 mM amiloride for 10 min, the salt response to NaCl was not affected. On the other hand, the sugar responses to sucrose, fructose, l-Val and l-Phe were depressed just after amiloride pretreatment. The sugar response to adenosine 5’-diphosphate (ADP) mixed with 0.5 mM amiloride was not depressed, but the response to ADP alone was depressed after amiloride pretreatment. It was therefore observed that amiloride depressed the responses to all stimulants that react with each of the receptor sites of the sugar receptor cell.     

Gustatory hairs on the mosquito, Culiseta inornata.

Gustatory hairs were investigated on the legs and mouthparts of Culiseta inornata (Williston) (Diptera: Culicidae). One type of hair, each innervated by four neurons, was found on the legs. Two of the neurons responded to NaCl stimulation, one neuron to water stimulation, and one neuron to sucrose stimulation. Three kinds of hairs designated Type I (T1), Type 2 (T2) and Type 3 (T3) were analyzed on the labella. The T1 hairs are innervated by one sugar neuron, one mechanoreceptor, two salt neurons and one water neuron. The T2 hairs are innervated by two salt neurons and one mechanoreceptor. The T3 hairs, located on the oral surface of the labella, are innervated by a variable number (2-5) of neurons. Precise identification of the T3 chemosensory neurons was not made because of the small size and inaccessibility of the T3 hairs. Chemosensory hairs on the tip of the labrum were tested electrophysiologically. the sequence of decreasing effeectiveness for the three salts tested was KCl greater than NaCl greater than LiCl. Labral chemoreceptors also responded positively to sucrose.     

Taste responses of Drosophila melanogaster

The amounts of sugar solution consumed by Drosophila melanogaster flies were determined. Starved and desiccated flies of a wild type strain (QA) consume 7?9 × 10^?2 λ of a 0.3 M sucrose solution per fly during the first hour and less later. They consume more of the 0.3 M sucrose solution than of the more diluted and the more concentrated solutions. In preference-aversion tests the flies discriminated between water and various sugar solutions, and between different sugar concentrations. Contrary to other fly species these flies did not prefer 0.05 M fructose over 0.05 M glucose. 0.3–0.5 M NaCl added to 0.1 M sucrose turned a preference over 0.01 sucrose into an aversion. A mutant, Lot-94, selected for its increased consumption of a 1 M NaCl solution was found to consume more of all test solutions. The amount of NaCl that had to be added to 0.1 M sucrose to turn the preference over 0.01 M sucrose by the mutant flies into aversion was not different from that found for the wild type flies.     

Oviposition by Lobesia botrana is stimulated by sugars detected by contact chemoreceptors

Abstract.  The influence of glucose, fructose and sucrose on oviposition site selection by Lobesia botrana is studied by combining behavioural and electrophysiological experiments. Oviposition choice assays, using surrogate grapes treated with grape berry surface extracts of Vitis vinifera cv. Merlot at different development stages, show that L. botrana females are most stimulated by extracts of mature berries containing the highest concentrations of glucose and fructose. Choice assays reveal that the oviposition response to these sugars is dose-dependant (with a threshold of the applied solution = 10 m m and a maximum stimulation at 1  m ) and that females are more sensitive to fructose than to glucose. Tarsal contact-chemoreceptor sensilla are unresponsive to stimulation with sugars but the ovipositor sensilla contain at least one neurone most sensitive to fructose and sucrose with a threshold of approximately 0.5 m m . Corresponding to the behavioural data, glucose is significantly less stimulatory to sensilla than fructose or sucrose. It is argued that fructose may be of special importance for herbivorous insects exploiting fruit as an oviposition site.     

Detection of alkaloids and carbohydrates by taste receptor cells of the galea of gypsy moth larvae, Lymantria dispar (L.)

Gypsy moth larvae are polyphagous feeders. The electrophysiological responses of the medial and lateral styloconic sensilla to four secondary compounds (e.g., alkaloids), two carbohydrates, and one inorganic salt were examined using an extracellular tip-recording method. In the medial sensillum, one taste receptor cell responded to the alkaloids, strychnine, caffeine, nicotine, and aristolochic acid (i.e., deterrent-sensitive cell), while another, responded to the sugar alcohol and inositol (inositol-sensitive cell). In both medial and lateral sensilla, two taste receptor cells in each sensillum responded minimally and sporadically to 30?mM potassium chloride (KCl) (i.e., KCl-sensitive cells); one cell produced much larger amplitude action potentials than the other. In the medial sensillum, only the large-amplitude KCl-sensitive cell exhibited an increased firing rate with increasing salt concentration. When binary mixture experiments were conducted, it was confirmed that the large-amplitude KCl-sensitive cell and the deterrent-sensitive cell in the medial sensillum were one in the same cell. Only a single cell in the lateral sensillum responded to the sugar, sucrose (sucrose-sensitive cell). The temporal dynamics of responses of the deterrent-sensitive, sucrose-sensitive, and inositol-sensitive cells were compared. Concentration?Cresponse data were obtained for the deterrent-sensitive cell to various alkaloids, as well as to KCl.     

High sensitivity to sodium in the sugar chemoreceptor of the cherry fruit fly after emergence

Abstract Recordings from the tarsal contact chemoreceptor D-sensilla of the cherry fruit fly (Rhagoletis cerasi, Dipt., Tephritidae) revealed the presence of a cell which had a variable sensitivity spectrum. In about 60% of the sensilla of freshly emerged flies this cell was found to be very sensitive to sodium and to a lesser degree to lithium cations. Potassium and other alkali cations were non-stimulatory. The anions tested, Cl^-, F^-, Br, NO₃^-, and CO₃^-, had no effect on the response to sodium. The same Na⁺-sensitive receptor cells fired in response to stimulation with sucrose plus NaCl or sucrose plus KCI mixtures and were therefore considered to be sugar cells. This was confirmed by cross-adaptation experiments using NaCl, and sucrose dissolved in dilute NaCl or KCI. However, the two adaptive stimuli were not acting symmetrically: NaCl did inhibit the following stimulation with sucrose, whereas sucrose had no effect on the subsequent NaCl stimulation. The response to sucrose and NaCl were not additive, sucrose being apparently, in some sensilla, inhibitory to the stimulation by NaCl. This observation, the lack of symmetry in adaptation, as well as the fact that only a proportion of the sensilla were sensitive to NaCl, seems to indicate that sodium had a different stimulating mechanism than sucrose. In most sensilla of flies older than 24 h, the Na⁺ sensitivity of the sugar cell was either reduced or completely lost. Behavioural observations of cherry fruit flies during the first 3 ½ days of adult life revealed that the flies fed little or not at all in the first 12 h. Thus the pronounced sodium sensitivity of the sugar cell early in adult life seems not to be correlated with a specific need for sodium intake but may have some role in the functioning of the sugar cell.     

Conformational change of poly-N epsilon-glutaryl-L-lysine and poly-N epsilon-succinyl-L-lysine in aqueous salt solutions

The conformational changes of poly-N^ε-glutaryl-L -lysine (PGL) and poly-N^ε-succinyl-L -lysine (PSL) in various salt solutions were studied by use of ORD and potentiometric titration measurements. The addition of alkali metal salts to the fully ionized PGL or PSL solution caused helix formation. The helical content of the polymers increases in the following sequences: at salt concentration 0–2 M, CsCl < KCl < LiCl < NaCl; and at 2–3 M, LiCl < CsCl < KCl ～ NaCl. The preferential binding of the solvent components with various alkali metal salts of PGL or PSL was measured in LiCl, NaCl, and KCl solutions by means of equilibrium dialysis and differential refractometry. It was found that with increasing salt concentration, the polymers were preferentially hydrated in NaCl and KCl soultions; however the salt was preferentially bound to the polymers in LiCl solution. Such preferential binding was suggested to be closely related to conformational change. The addition of CaCl₂ to polymer solutions led to the stabilization of the helical structure of PGL or PSL.     

Mechanism of inhibitory action by salts in the feeding behaviour of the blowfly, Phormia regina

Blowfly proboscis extension during stimulation of labellar sugar receptors can be inhibited by the presence of salt. The possibility that the salt receptor might initiate a central nervous inhibitory state is investigated behaviourally and electrophysiologically using simultaneous recordings from labellar chemoreceptors and the extensor muscle of the haustellum. While a mixture of 100 mM sucrose and 4 M NaCl applied to a single sensillum does cause inhibition, the same compounds applied separately simultaneously on separate sensilla do not. A mixture of 100 mM sucrose and 4 M NaCl does not produce central nervous effects such as motor response decrement to repeated stimulation; nor does it produce an enhanced motor response resulting from cross-channel summation when applied simultaneously with 100 mM sucrose on another sensillum. These results argue that the inhibitory effect of mixtures containing sugar and salt can be explained by inhibition of the sugar receptor without having to invoke a central inhibitory mechanism.     

Osmotic Effects on Membrane Permeability in a Marine Bacterium

When cells of Alteromonas haloplanktis 214 (ATCC 19855) were preloaded with α-[¹⁴C]aminoisobutyric acid or the K⁺ in the cells was labeled with ⁴²K by incubation in a buffered salt solution containing 0.05 M MgSO₄, 0.01 M KCl, and 0.3 M NaCl, the cells retained their radioactivity when resuspended in the same salt solution. When NaCl was omitted from the solution, 80 to 90% of the radioactivity was lost from the cells. Cells suspended at intermediate concentrations of NaCl also lost radioactivity. New steady-state levels of the intracellular solutes were established within 15 s of suspending the cells; the percentage of radioactivity retained at each level decreased proportionately as the osmolality of the NaCl in the suspending solution decreased. With minor variations in effectiveness, MgCl₂, LiCl, and sucrose could substitute for NaCl on an equiosmolal basis for the retention of radioactivity by the cells. KCl, RbCl, and CsCl were appreciably less effective as replacements for NaCl, particularly when their osmolalities in the suspending solutions were low. The amount of α-[¹⁴C]aminoisobutyric acid taken up by the cells at the steady-state level increased to a maximum as the NaCl concentration in the suspending medium increased to 0.3 M. At suboptimal levels of NaCl, either LiCl or sucrose could substitute for NaCl in increasing the steady-state levels. The results obtained indicate that the porosity of the cytoplasmic membrane of this organism is determined by the difference between the osmotic pressure of the cytoplasm and the suspending medium. The lesser effectiveness of K⁺, Rb⁺, and Cs⁺ than Na⁺, Li, or Mg²⁺ in permitting the retention of solutes by the cells is attributed to the greater penetrability of the hydrated ions of the former group through the dilated pores of a stretched cytoplasmic membrane.     

Antennal sugar sensitivity in the click beetle Agriotes obscurus

The occurrence of salt‐, sugar‐sensitive neurones and a mechanoreceptor neurone in the antennal hair‐like gustatory sensilla of the click beetle Agriotes obscurus L. (Coleoptera, Elateridae) is demonstrated using the electrophysiological sensillum tip‐recording technique. The stimulating effect of 13 water soluble sugars at 100 mm is tested on the neurones of these sensilla. Sucrose and fructose are the two most stimulating sugars for the sugar‐sensitive neurone, evoking almost 30 spikes s^?1 at 100 mm . The stimulating effect of arabinose, glucose, mannose, maltose and raffinose is three‐ to five‐fold lower, in the range 5.9–9.6 spikes s^?1. The remaining six sugars, xylose, galactose, rhamnose, cellobiose, trehalose and lactose, have very low (<1 spikes s^?1) or no ability to stimulate the sugar‐sensitive neurone. Concentration/response curves of the sugar‐sensitive neurone to sucrose, fructose and glucose at 0.01–100 mm overlap to a large extent in hibernating, cold reactivated and reproductively‐active beetles. A remarkable 9–50% decrease in the number of spikes evoked by 100 mm fructose and 10–100 mm sucrose occurs, however, in reproductively‐active beetles in June compared with beetles at the beginning of hibernation in October. These findings show that A. obscurus is capable of sensing a wide range sugars via their antennal gustatory sensilla.     

Sugar-activated ion transport in canine lingual epithelium. Implications for sugar taste transduction

There is good evidence indicating that ion-transport pathways in the apical regions of lingual epithelial cells, including taste bud cells, may play a role in salt taste reception. In this article, we present evidence that, in the case of the dog, there also exists a sugar-activated ion-transport pathway that is linked to sugar taste transduction. Evidence was drawn from two parallel lines of experiments: (a) ion-transport studies on the isolated canine lingual epithelium, and (b) recordings from the canine chorda tympani. The results in vitro showed that both mono- and disaccharides in the mucosal bath stimulate a dose-dependent increase in the short-circuit current over the concentration range coincident with mammalian sugar taste responses. Transepithelial current evoked by glucose, fructose, or sucrose in either 30 mM NaCl or in Krebs-Henseleit buffer (K-H) was partially blocked by amiloride. Among current carriers activated by saccharides, the current response was greater with Na than with K. Ion flux measurements in K-H during stimulation with 3-O-methylglucose showed that the sugar-evoked current was due to an increase in the Na influx. Ouabain or amiloride reduced the sugar-evoked Na influx without effect on sugar transport as measured with tritiated 3-O-methylglucose. Amiloride inhibited the canine chorda tympani response to 0.5 M NaCl by 70-80% and the response to 0.5 M KCl by approximately 40%. This agreed with the percent inhibition by amiloride of the short-circuit current supported in vitro by NaCl and KCl. Amiloride also partially inhibited the chorda tympani responses to sucrose and to fructose. The results indicate that in the dog: (a) the ion transporter subserving Na taste also subserves part of the response to K, and (b) a sugar-activated, Na-preferring ion-transport system is one mechanism mediating sugar taste transduction. Results in the literature indicate a similar sweet taste mechanism for humans.     

Studies on the interaction between alkali metal cations and polyion by sound velocity

The sound velocities in polyelectrolyte solutions were measured at various concentrations of added salts. When aqueous solutions of tetra (n-butyl)ammonium polyacrylate were titrated with concentrated solutions of LiCl, NaCl, KCl or CsCl, the sound velocity, i.e., the adiabatic compressibility of the solution, did not change linearly with added salt concentration, but showed a breaking point. The degrees of counterion binding on polyacrylate ion estimated from the breaking points were 0.25-0.30, independent of cation species. In polystyrenesulfonate, moreover, no Na+ binding was detected from such sound velocity measurements.     

Characterization of <Emphasis Type="Italic">SWEET</Emphasis> family members from loquat and their responses to exogenous induction

The plant SWEET family is a sugar transporter family that plays a significant role in plant development. Here, seven loquat SWEET family members were identified by RNA-seq. These were designated as EjSWEET1, EjSWEET2a, EjSWEET2b, EjSWEET2c, EjSWEET4, EjSWEET15, and EjSWEET17. Phylogenetic and predictive functional annotation analyses suggest that the loquat SWEETs are classified as having sucrose, glucose and fructose transportation features. The in vivo responses of loquat SWEETs to exogenous sugar or NaCl was investigated by applying high concentrations of sugar or salt to 7-month-old loquat seedlings cultured in a nutrient medium. The results showed that most loquat SWEET genes can respond to exogenous applications of sucrose, glucose, fructose and salt. The response of EjSWEET1 to exogenous fructose was faster than the others, indicating that EjSWEET1 is more sensitive to exogenous fructose compared with other loquat SWEETs. EjSWEET15 can be induced by sucrose, but is suppressed by glucose. This indicates its possible role in sucrose transporting. The response of loquat SWEETs to NaCl showed broadly similar patterns compared to sugars. However, after a longer time of NaCl treatment, most loquat SWEETs are upregulated, especially EjSWEET15. This indicates its long-term response to high salinity.     

Ingestion of sugar diets correlates with spike activity in labellar chemosensilla of the flesh-fly, Neobellieria (= Sarcophaga ) bullata

Abstract .Female 2-day-old Neobellieria (= Sarcophaga ) bullata (Parker) (Diptera: Sarcophagidae) were exposed to different concentrations of sucrose, glucose and fructose in a single-choice potometer, and the volume ingested in the first hour was measured. Nerve spike activity in response to the same sugars was recorded from medium labellar taste hairs of similar flies by tip-recording. Two classes of chemosensory cells responded to sucrose, glucose and fructose. Cell 1 showed an increasing spike activity with sugar concentration, whereas cell 2 did not; cell 1 was identified as the 'sugar cell'.
For both spike activity in cell 1 and feeding, sucrose was the most stimulatory sugar. The dose–response curves for glucose and fructose crossed over at about 200 m m . At higher concentrations, glucose was more stimulatory for both cell 1 and for feeding, and at lower concentrations, fructose. The pattern of spike activity supports a separate location on the sensory cells of receptors for pyranose and fructose forms of sugar. The strong correlation between volume ingested and spike activity indicates that sugar feeding is controlled by sensory input from the 'sugar' cells of labellar chemosensilla. Moreover, the results suggest that the flies do not distinguish between these sugars except by apparent 'sweetness'.     

Partitioning of carbohydrates in salt-sensitive and salt-tolerant soybean callus cultures under salinity stress and its subsequent relief

Salt tolerant (R100) and sensitive (S100) cell lines of Glycine max (L.) that differ in their ability to accumulate sodium (Na) and chloride (Cl) under 100 mM salt stress, were used to compare the contribution of carbohydrates in osmotic adjustment. Calliwere exposed to a 100 mM NaCl concentrations for 12 days followed by 16 days of relief from stress to determine the effect of salinity changes of sugar content in the two cell lines. The salt-tolerant and the salt-sensitive cell lines differed in the time at which, and the type of sugar, that increased during salt stress. However, recovery in sugar content parameters during relief from stress were similar in the two cell lines. The concentration of glucose and fructose increased at a rate closely corresponding to the increase in fresh weight, while the concentration of sucrose decreased to the control level coincident with relatively rapid growth.     

In Vitro Sugar Transport in Zea mays L. Kernels : I. Characteristics of Sugar Absorption and Metabolism by Developing Maize Endosperm

Short-term transport studies were conducted using excised whole Zea mays kernels incubated in buffered solutions containing radiolabeled sugars. Following incubation, endosperms were removed and rates of net ¹⁴C-sugar uptake were determined. Endogenous sugar gradients of the kernel were estimated by measuring sugar concentrations in cell sap collected from the pedicel and endosperm. A sugar concentration gradient from the pedicel to the endosperm was found. Uptake rates of ¹⁴C-labeled glucose, fructose, and sucrose were linear over the concentration range of 2 to 200 millimolar. At sugar concentrations greater than 50 millimolar, hexose uptake exceeded sucrose uptake. Metabolic inhibitor studies using carbonylcyanide-m-chlorophenylhydrazone, sodium cyanide, and dinitrophenol and estimates of Q₁₀ suggest that the transport of sugars into the developing maize endosperm is a passive process. Sucrose was hydrolyzed to glucose and fructose during uptake and in the endosperm was either reconverted to sucrose or incorporated into insoluble matter. These data suggest that the conversion of sucrose to glucose and fructose may play a role in sugar absorption by endosperm. Our data do not indicate that sugars are absorbed actively. Sugar uptake by the endosperm may be regulated by the capacity for sugar utilization (i.e. starch synthesis).     

MICRURGICAL STUDIES IN CELL PHYSIOLOGY : V. THE ANTAGONISM OF CATIONS IN THEIR ACTIONS ON THE PROTOPLASM OF AM?BA DUBIA.

I. The Plasmalemma. 1. On the plasmalemma of amebæ CaCl₂ antagonizes the toxic action of LiCl better than it does NaCl, and still better than it does KCl. MgCl₂ antagonizes the toxic action of NaCl better than it does LiCl and still better than it does KCl. 2. CaCl₂ antagonizes the toxic action of LiCl and of KCl better than does MgCl₂: MgCl₂ antagonizes NaCl better than does CaCl₂. II. The Internal Protoplasm. 3. The antagonizing efficiency of CaCl₂ and of MgCl₂ are highest against the toxic action of KCl on the internal protoplasm, less against that of NaCl, and least against that of LiCl. 4. CaCl₂ antagonizes the toxic action of LiCl better than does MgCl₂: MgCl₂ antagonizes the toxic action of NaCl and of KCl better than does CaCl₂. 5. LiCl antagonizes the toxic action of MgCl₂ on the internal protoplasm more effectively than do NaCl or KCl, which have an equal antagonizing effect on the MgCl₂ action. III. The Nature of Antagonism. 6. When the concentration of an antagonizing salt is increased to a toxic value, it acts synergistically with a toxic salt. 7. No case was found in which a potentially antagonistic salt abolishes the toxic action of a salt unless it is present at the site (surface or interior) of toxic action. 8. Antagonistic actions of the salts used in these experiments are of differing effectiveness on the internal protoplasm and on the surface membrane.