Effects of inotropic agents on contraction and relaxation of papillary muscle.

The effects of epinephrine and caffeine on isometric rabbit papillary muscle preparations were observed after maximum peak tension was produced by adjustment of initial length and Ca⁺⁺ concentration. Without change in peak tension, epinephrine caused increased positive dP/dt (p < .005), increased negative dP/dt (p < .001) and decreased time to peak tension (TP) (p < .001), while caffeine resulted in decreased positive dP/dt (p < .02), decreased negative dP/dt (p < .005) and prolonged TP (p < .001). Caffeine added to muscles being perfused with epinephrine reversed the epinephrine effects. The data suggest that epinephrine increases the influx of Ca⁺⁺ into the cell and the uptake of Ca⁺⁺ by the sarcoplasmic reticulum, and that caffeine exerts opposite effects on Ca⁺⁺ exchange. However, an additional mechanism not dependent on changes in Ca⁺⁺ flux is suggested. Epinephrine and caffeine may directly effect the rates of actin-myosin interaction, the former agent increasing, the latter decreasing the rates of attachment and detachment of actin-myosin bridges.     

Role of external calcium in sodium and chloride transport in the gills of seawater-adaptedMugil capito

Summary When the mulletMugil capito is transferred to medium lacking Ca⁺⁺ (either Ca⁺⁺-free seawater or distilled water) the passive permeability of the gill to Na⁺ and Cl^– is increased and the activating effect of external K⁺ on the Na⁺ and Cl^– effluxes in hyposaline media is inhibited. The permeability of the gill increases progressively in proportion to the time of Ca⁺⁺ deprivation; it declines when Ca⁺⁺ is added again to the external medium. The active mechanisms for ion excretion are not reversible. At external Ca⁺⁺ concentrations from 0.1 to 10 mM the Na⁺ permeability is constant but the activation of Na⁺ efflux by K⁺ shows a maximum at a Ca⁺⁺ concentration of about 1 mM. For activation of Cl^– efflux external bicarbonate must be present, in addition to Ca⁺⁺, suggesting the existence of a Cl^–/HCO ₃ ^– exchange. The mechanism by which Ca⁺⁺ controls the passive branchial permeability is thus probably different from that involved in K⁺ activation of ion excretion. The Ca⁺⁺ effect on the K⁺ sensitive ionic excretory mechanisms seems to be related to intracellular Ca⁺⁺ movements. Thus, on the one hand, substances such as Ruthenium Red and La⁺⁺⁺ which both inhibit Ca⁺⁺ exchange, in media containing Ca⁺⁺ and HCO ₃ ^– also inhibit K⁺ activation of Na⁺ and Cl^– effluxes; on the other hand, the ionophore A 23187, a stimulator of Ca⁺⁺ exchange, when added to these media, activates the Na⁺ and Cl^– effluxes; its maximal effect on the Na⁺ flux occurs at 2 mM Ca⁺⁺.Abbreviations ASW-Ca artificial seawater minus calcium - DW deionised water - DWCa deionised water with 1 mM Ca⁺⁺ added - DWCaHCO ₃ DW with calcium plus bicarbonate - DWHCO ₃ DW with 1 mM sodium bicarbonate added - FW freshwater (tap water) - FWK freshwater with K⁺ added - P. D. potential difference - SW seawater The experiments reported in this paper were done with Jean Maetz who tragically died in August 1977. It is the last report about several years of friendly collaboration     

Appearance and maturation of voltage-dependent conductances in solitary spiking cells during retinal regeneration in the adult newt

Summary Electrical membrane properties of solitary spiking cells during newt (Cynops pyrrhogaster) retinal regeneration were studied with whole-cell patch-clamp methods in comparison with those in the normal retina.The membrane currents of normal spiking cells consisted of 5 components: inward Na⁺ and Ca⁺⁺ currents and 3 outward K⁺ currents of tetraethylammonium (TEA)-sensitive, 4-aminopyridine (4-AP)-sensitive, and Ca⁺⁺-activated varieties. The resting potential was about -40mV. The activation voltage for Na⁺ and Ca⁺⁺ currents was about -30 and -17 mV, respectively. The maximum Na⁺ and Ca⁺⁺ currents were about 1057 and 179 pA, respectively.In regenerating retinae after 19–20 days of surgery, solitary cells with depigmented cytoplasm showed slowrising action potentials of long duration. The ionic dependence of this activity displayed two voltage-dependent components: slow inward Na⁺ and TEA-sensitive outward K⁺ currents. The maximum inward current (about 156 pA) was much smaller than that of the control. There was no indication of an inward Ca⁺⁺ current.During subsequent regeneration, the inward Ca⁺⁺ current appeared in most spiking cells, and the magnitude of the inward Na⁺, Ca⁺⁺, and outward K⁺ currents all increased. By 30 days of regeneration, the electrical activities of spiking cells became identical to those in the normal retina. No significant difference in the resting potential and the activation voltage for Na⁺ and Ca⁺⁺ currents was found during the regenerating period examined.     

Ca++ fluxes in resealed synaptic plasma membrane vesicles

The effect of the monovalent cations Na⁺, Li⁺, and K⁺ on Ca⁺⁺ fluxes has been determined in resealed synaptic plasma membrane vesicle preparations from rat brain. Freshly isolated synaptic membranes, as well as synaptic membranes which were frozen (?80°C), rapidly thawed, and passively loaded with K₂/succinate and ⁴⁵CaCl₂, rapidly released approximately 60% of the intravesicular Ca⁺⁺ when exposed to NaCl or to the Ca⁺⁺ ionophore A 23187. Incubation of these vesicles with LiCl caused a lesser release of Ca⁺⁺. The EC₅₀ for Na⁺ activation of Ca⁺⁺ efflux from the vesicles was approximately 6.6mM. exposure of the Ca⁺⁺-loaded vesicles to 150 mM KCl produced a very rapid (?1 sec) loss of Ca⁺⁺ from the vesicles, but the Na⁺-induced efflux could still be detected above this K⁺ - sensitive effect. Vesicles pre-loaded with NaCl (150 mM) exhibited rapid ⁴⁵Ca uptake with an estimated EC₅₀ for Ca⁺⁺ of 7–10 μM. This Ca⁺⁺ uptake was blocked by dissipation of the Na⁺ gradient. These observations are suggestive of the preservation in these purified frozen synaptic membrane preparations of the basic properties of the Na⁺Ca⁺⁺ exchange process and of a K⁺ - sensitive Ca⁺⁺ flux across the membranes.     

Effect of different water salinity levels and organic matter application on the composition of water soluble and exchangeable bases in a brackishwater fish pond soil

Behaviour of different water soluble and exchangeable bases in a brackishwater fish pond soil was studied under four levels of water salinity, in combination with and without organic matter application. The results showed average content of water soluble bases to increase with increase in water salinity. The bases were dominated by Na⁺ followed by Mg⁺⁺, Ca⁺⁺ and K⁺ in decreasing order. SAR values of water increased with increase in water salinity and decreased slightly on organic matter treatment.Total content of exchangeable bases in soils was fairly high and was dominated by Ca⁺⁺ and Mg⁺⁺, followed by Na⁺ and K⁺ respectively. Amount of exchangeable Ca⁺⁺ + Mg⁺⁺ decreased while that of Na⁺ increased with increase in water salinity levels. Amount of exchangeable K⁺ did not show any appreciable change. Application of organic matter tended to increase the exchangeable Ca⁺⁺ + Mg⁺⁺ content and decrease the amount of exchangeable Na⁺ in the soil, while exchangeable K⁺ content remained practically unaffected due to organic matter treatment.Formed part of a Ph.D. thesis submitted to Bidhan Chandra Agricultural University, India in 1978Formed part of a Ph.D. thesis submitted to Bidhan Chandra Agricultural University, India in 1978     

Regulation of cardiac sarcolemmal Ca2+ channels and Ca2+ transporters by thyroid hormone

In order to examine the regulatory role of thyroid hormone on sarcolemmal Ca²⁺-channels, Na⁺–Ca²⁺ exchange and Ca²⁺-pump as well as heart function, the effects of hypothyroidism and hyperthyroidism on rat heart performance and sarcolemmal Ca²⁺-handling were studied. Hyperthyroid rats showed higher values for heart rate (HR), maximal rates of ventricular pressure development+(dP/dt)max and pressure fall–(dP/dt)max, but shorter time to peak ventricular pressure (TPVP) and contraction time (CT) when compared with euthyroid rats. The left ventricular systolic pressure (LVSP) and left ventricular end-diastolic pressure (LVEDP), as well as aortic systolic and diastolic pressures (ASP and ADP, respectively) were not significantly altered. Hypothyroid rats exhibited decreased values of LVSP, HR, ASP, ADP, +(dP/dt)max and –(dP/dt)max but higher CT when compared with euthyroid rats; the values of LVEDP and TPVP were not changed. Studies with isolated-perfused hearts showed that while hypothyroidism did not modulate the inotropic response to extracellular Ca²⁺ and Ca²⁺ channel blocker verapamil, hyperthyroidism increased sensitivity to Ca²⁺ and decreased sensitivity to verapamil in comparison to euthyroid hearts. Studies of [³H]-nitrendipine binding with purified cardiac sarcolemmal membrane revealed decreased number of high affinity binding sites (B_max) without any change in the dissociation constant for receptor-ligand complex (K_d) in the hyperthyroid group when compared with euthyroid sarcolemma; hypothyroidism had no effect on these parameters. The activities of sarcolemmal Ca²⁺-stimulated ATPase, ATP-dependent Ca²⁺ uptake and ouabain-sensitive Na⁺–K⁺ ATPase were decreased whereas the Mg²⁺-ATPase activity was increased in hypothyroid hearts. On the other hand, sarcolemmal membranes from hyperthyroid samples exhibited increased ouabain-sensitive Na⁺–K⁺ ATPase activity, whereas Ca²⁺-stimulated ATPase, ATP-dependent Ca²⁺ uptake, and Mg²⁺-ATPase activities were unchanged. The V_max and K_a for Ca²⁺ of cardiac sarcolemmal Na⁺–Ca²⁺ exchange were not altered in both hyperthyroid and hypothyroid states. These results indicate that the status of sarcolemmal Ca²⁺-transport processes is regulated by thyroid hormones and the modification of Ca²⁺-fluxes across the sarcolemmal membrane may play a crucial role in the development of thyroid state-dependent contractile changes in the heart.     

Early changes of 'leak flux' and the cation content of lymphocytes by concanavalin A.

The leak fluxes of Na⁺, K⁺, Mg⁺⁺ and Ca⁺⁺ in mouse thymocytes are increased by Concavaline A (Con A), within minutes after mitogen addition. The intracellular Mg⁺⁺ and K⁺ concentrations were decreased and the Na⁺ and Ca⁺⁺ contents were increased by Con A in mouse thymocytes and spleen cells.     

Binding of cations by microsomes from rabbit skeletal muscle

Fragmented sarcoplasmic reticulum and transverse tubular system, as isolated in the microsomal fraction from rabbit skeletal muscle, bind H⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, and Zn⁺⁺. The binding depends on a cation exchange type of interaction between these cations and the chemical components of the membranous systems of the muscle cell. The monovalent and divalent cations exchange quantitatively for each other at the binding sites on an equivalent basis. Scatchard plots of the H⁺ binding data indicate that the binding groups can be resolved into two major components in terms of their pK values. Component 1 has a pK value of 6.6 and a capacity for H⁺ binding of 2.2 meq/g N . The second component has a much higher H⁺ binding capacity (7–8 meq/g N ), but its pK value, 3.4, is non-physiological. The binding of cations other than H⁺ at a neutral pH occurs at the binding sites making up component 1. The order of affinity of the cations for the microsome binding sites is H⁺ » Zn⁺⁺ > Ca⁺⁺ > Mg⁺⁺ » Na⁺ = K⁺ as reflected by the apparent respective pK_M values: 6.6, 5.2, 4.7, 4.2, 1.3, 1.3. Caffeine, which causes contracture and potentiates the twitch of skeletal muscle, does not interfere with the binding of Ca⁺⁺ by the microsomes at neutral pH.     

Calcium entry in rabbit corneal epithelial cells: Evidence for a nonvoltage dependent pathway

We performed experiments to elucidate the calcium influx pathways in freshly dispersed rabbit corneal epithelial cells. Three possible pathways were considered: voltage-gated Ca⁺⁺ channels, Na⁺/Ca⁺⁺ exchange, and nonvoltage-dependent Ca⁺⁺-permeable channels. Whole cell inward currents carrying either Ca⁺⁺ or Ba⁺⁺ were not detected using voltage clamp techniques. We also used imaging technology and the Ca⁺⁺-sensitive ratiometric dye fura 2 to measure changes in intracellular Ca⁺⁺ concentration ([Ca]_i). Bath perfusion with NaCl Ringer's solution containing the calcium channel agonist Bay-K-8644 (1 m), or Ni⁺⁺ (40 m), a blocker of many voltage-dependent calcium channels, did not affect [Ca⁺⁺]_i. Membrane depolarization with a KCl Ringer's bath solution resulted in a decrease in [Ca⁺⁺]_i. These results are inconsistent with the presence of voltage gated Ca⁺⁺ channels. Nonvoltage gated Ca⁺⁺ entry, on the other hand, would be reduced by membrane depolarization and enhanced by membrane hyperpolarization. Agents which hyperpolarize via stimulation of K⁺ current, such as flufenamic acid, resulted in an increase in ratio intensity. The cells were found to be permeable to Mn⁺⁺ and bath perfusion with 5 mm Ni⁺⁺ decreased [Ca⁺⁺]_i suggesting that the Ca⁺⁺ conductance was blocked. These results are most consistent with a nonvoltage gated Ca⁺⁺ influx pathway. Finally, replacing extracellular Na⁺ with Li⁺ resulted in an increase in [Ca⁺⁺]_i if the cells were first Na⁺-loaded using the Na⁺ ionophore monensin and ouabain, a Na⁺-K⁺-ATPase inhibitor. These results suggest that Na⁺/Ca⁺⁺ exchange may also regulate [Ca⁺⁺] in this cell type.The authors are grateful to Chris Bartling for expert technical assistance with the imaging experiments, Helen Hendrickson for cell preparation, and Jonathon Monck for helpful discussions regarding imaging technology. This work was supported by National Institutes of Health grants EYO3282, EYO6005, DK08677, and an unrestricted award from Research to Prevent Blindness.     

Bioelectric effects of ions microinjected into the giant axon of Loligo

1. A technique is described for recording the bioelectric activity of the squid giant axon during and following alteration of the internal axonal composition with respect to ions or other substances. 2. Experimental evidence indicates that the technique as described is capable of measuring changes in local bioelectric activity with an accuracy of 10 to 15 per cent or higher. 3. Alterations of the internal K⁺ or Cl^- concentrations do not cause the change in resting potential expected on the basis of a Donnan mechanism. 4. The general effect of microinjection of K⁺ Rb⁺, Na⁺, Li⁺, Ba⁺⁺, Ca⁺⁺, Mg⁺⁺, or Sr⁺⁺ is to cause decrease in spike amplitude, followed by propagation block. 5. The resting potential decreases when the amplitude of the spike becomes low and block is incipient. 6. The decrease in resting potential and spike amplitude may be confined to the immediate vicinity of the injection. 7. At block, the resting potential decreases up to 50 per cent, but injection of small quantities of divalent cations may cause much larger localized depolarization. 8. The blocking effectiveness of K⁺, Na⁺, and Ca⁺⁺ expressed as reciprocals of the relative amounts needed to cause block is approximately 1:5:100. Rb⁺ has the same low effectiveness as does K⁺. Li⁺ resembles Na⁺. Ba⁺⁺ and Mg⁺⁺ are approximately as effective as Ca⁺⁺. 9. Microinjection of Na⁺ may cause marked prolongation of the spike at the injection site as well as decrease in its amplitude. 10. The anions used (Cl^-, HCO₃^-, NO₃^-, SO₄^-, aspartate, and glutamate) do not seem to exert specific effects. 11. A tentative explanation is offered for the insensitivity of the resting potential to changes in the axonal ionic composition. 12. New data are presented on the range of variation, in a large sample, of the magnitude of the resting potential and spike amplitude.     

A highly ion-sensitive ATP-phosphorylation system in lobster nerve

The transfer of -phosphate from ³²P labeled adenosine-triphosphate (ATP) at low concentrations (10^?10 to 10^?7M) into the peripheral nerve of the lobster was found to be highly sensitive to external ionic environments. The phosphorylation process is inhibited at conditions similar to extracellular environments (high Na⁺, Ca⁺⁺ and pH) and stimulated by those close to intracellular medium (high K⁺, Mg⁺⁺ and low pH). This system is not related to NaK ATPase (pump ATPase) which is highly sensitive to ouabain and is active only at higher ATP concentrations (>10^?6M). The system is membrane bound and sensitive to a variety of neuro-active agents which are known to interfere with ionic conductance changes in axons.     

The penetration of some cations into muscle

The influx of Na⁺, K⁺, Rb⁺, and Cs⁺ into frog sartorius muscle has been followed. The results show that a maximum rate is found for K⁺, while Na⁺ and Cs⁺ penetrate much more slowly. Similar measurements with Ca⁺⁺, Ba⁺⁺, and Ra⁺⁺ show that Ba⁺⁺ penetrates at a rate somewhat greater than that of either Ca⁺⁺ or Ra⁺⁺. All these divalent cations, however, penetrate at rates much slower than do the alkali cations. The results obtained are discussed with reference to a model that has been developed to explain the different penetration rates for the alkali cations.     

The effects of intracellular iontophoretic injection of calcium and sodium ions on the light response of Limulus ventral photoreceptors

During intracellular iontophoretic injection of Ca⁺⁺ into Limulus ventral photoreceptor cells, there is a progressive diminution of the light response. Following Ca⁺⁺ injection, the size of the light response slowly recovers. Similarly, there is a progressive diminution of the light response during intracellular injection of Na⁺ and recovery after the injection is stopped. The rate of diminution during Na⁺ injection is greater for higher [Ca⁺⁺]_out. In solutions which contain 0.1 mM Ca⁺⁺, there is nearly no progressive decrease in the size of the light response during Na⁺ injection. Intracellular injections of Li⁺ or K⁺ do not progressively decrease the size of the light response. We propose that an increase in [Na⁺]_in leads to an increase in [Ca⁺⁺]_in and that an increase in [Ca⁺⁺]_in by any means leads to a reduction in responsiveness to light.     

The Roles of Sodium and Potassium Ions in the Generation of the Electro-Olfactogram

In order to clarify whether or not the electronegative olfactory mucosal potentials (EOG) are generator potentials, the effects of changed ionic enviroment were studied. The EOG decreased in amplitude and in some cases nearly or completely disappeared, when Na⁺ in the bathing Ringer solution was replaced by sucrose, Li⁺, choline⁺, tetraethylammonium⁺ (TEA), or hydrazine. In the K⁺-free Ringer solution, the negative EOG's initially increased and then decreased in amplitude. In Ringer's solution with increased K⁺, the negative EOG's increased in amplitude. When K⁺ was increased in exchange for Na⁺ in Ringer's solution, the negative EOG's decreased, disappeared, and then reversed their polarity (Fig. 6). Next, when the K⁺ was replaced by equimolar sucrose, Li⁺, choline⁺, TEA⁺, hydrazine, or Na⁺, the reversed potentials recovered completely only in Na⁺-Ringer's solution, but never in the other solutions. Thus, the essential role of Na⁺ and K⁺ in the negative EOG's was demonstrated. Ba⁺⁺ was found to depress selectively the electropositive EOG, but it hardly decreased and never increased the negative EOG. Hence, it is concluded that Ba⁺⁺ interferes only with Cl^- influx, and that the negative EOG's are elicited by an increase in permeability of the olfactory receptive membrane to Na⁺ and K⁺, but not to Cl^-. From the ionic mechanism it is inferred that the negative EOG's are in most cases composites of generator and positive potentials.     

Further Studies on the Roles of Sodium and Potassium in the Generation of the Electro-Olfactogram : Effects of mono-, di-, and trivalent cations

In the negative EOG-generating process a cation which can substitute for Na⁺ was sought among the monovalent ions, Li⁺, Rb⁺, Cs⁺, NH₄⁺, and TEA⁺, the divalent ions, Mg⁺⁺, Ca⁺⁺, Sr⁺⁺, Ba⁺⁺, Zn⁺⁺, Cd⁺⁺, Mn⁺⁺, Co⁺⁺, and Ni⁺⁺, and the trivalent ions, Al⁺⁺⁺ and Fe⁺⁺⁺. In Ringer solutions in which Na⁺ was replaced by one of these cations the negative EOG's decreased in amplitude and could not maintain the original amplitudes. In K⁺-Ringer solution in which Na⁺ was replaced by K⁺, the negative EOG's reversed their polarity. Recovery of these reversed potentials was examined in modified Ringer solutions in which Na⁺ was replaced by one of the above cations. Complete recovery was found only in the normal Ringer solution. Thus, it was clarified that Na⁺ plays an irreplaceable role in the generation of the negative EOG's. The sieve hypothesis which was valid for the positive EOG-generating membrane or IPSP was not found applicable in any form to the negative EOG-generating membrane. The reversal of the negative EOG's found in K⁺- , Rb⁺- , and Ba⁺⁺-Ringer solutions was attributed to the exit of the internal K⁺. It is, however, not known whether or not Cl^- permeability increases in these Na⁺-free solutions and contributes to the generation of the reversed EOG's.     

In-vitro-studies on the influence of cations, neurotransmitters and tubocurarine on calcium-ganglioside-interactions.

The influence of K⁺, Na⁺, Mg⁺⁺, Li⁺, a serotonin, acetylcholine and tubocurarine on calcium-ganglioside-interactions was studied by way of equilibrium dialysis using ⁴⁵Ca as tracer. Experiments were carried out at 22 °C and 4 °C, respectively. The concentrations of the substances were in the range of physiologically relevant conditions. Cations caused a release of Ca⁺⁺ from calcium-ganglioside-complexes in the sequence of their molar efficiency: Mg⁺⁺ ≈ Li⁺ > K⁺ ≈ Na⁺. Tubocurarine, serotonin and acetylcholine also affected calcium-ganglioside-interactions. Ca⁺⁺ was displaced from ganglioside most effectively by tubocurarine, followed by serotonin, whereas acetylcholine competed considerably more weakly.     

Ionic Resistance in Strains of the Tetrahymena pyriformis Complex1

ABSTRACT. Strains of Tetrahymena thermophila were examined in an attempt to establish what role certain ions (Na⁺, K⁺, Li⁺, Ba⁺⁺, Ca⁺⁺, Mg⁺⁺, Mn⁺⁺, Al⁺⁺⁺, Fe⁺⁺⁺) play in influencing cell survival time in a culture medium. In short-term experiments (20–30 min), cell survival time in a 1% peptone medium is directly related to the valence of the ion employed. Long-term observations (lasting up to five days) in a 1% peptone medium containing lower ion concentrations revealed that the effects on cell-cycle time are not correlated with the valence state of the ion. Comparisons were made among the ionic resistances of strains of T. thermophila, of T. pyriformis sensu stricto, and of two subspecies of T. pigmentosa. Strains within a species are highly correlated in their patterns of ionic response, while marked differences between species occur. The most distinctive group of strains examined came from one of the subspecies (syngen 6) of T. pigmentosa.     

Effects of valinomycin on lymphocytes independent of potassium permeability

10^?7 M valinomycin affects human lymphocytes in the following manner: (1) it is non-toxic; (2) it inhibits mitogenesis; (3) it causes a reduction in cell ATP; and (4) it causes a marked increase in steady-state Na⁺ exchange. However, it has a minimal effect on cell ion (K⁺, Na⁺, Ca²⁺, Mg²⁺) contents and no effect whatever on K⁺ exchange. Neither the fast nor the slow fraction of steady-state K⁺ exchange is affected by 10^?7 M valinomycin. The various reported effects of valinomycin on lymphocyte functions cannot be assumed to be due to changes in plasma membrane K⁺ permeability. The mechanism of the increase in steady-state Na⁺ exchange, and whether or not it is related to inhibition of mitogenesis, are unsettled issues.     

A study of sodium release in the course of ATP hydrolysis by membrane ATPase

Summary With the aid of sodium-sensitive glass electrodes, changes in sodium ion activity were studied in the course of subsequent additions of components required for ATP hydrolysis provided by Na⁺–K⁺-dependent membrane ATPase. Membrane ATPase was obtained from guinea pig kidney cortex. In the presence of ATP, Mg⁺⁺ and Na⁺ in media, the addition of K⁺ caused an increase in Na⁺ activity. The omission of ATP or its substitution by ADP as well as the addition of Ca⁺⁺ to the media eliminated the above-mentioned increase of Na⁺ activity. Quabain did not affect Na⁺ release caused by the addition of K⁺, although it significantly inhibited ATPase activity of the preparation. The data obtained were considered to be a direct indication of ion exchange during the course of membrane ATPase reaction. This ion-exchange stage of the reaction is not inhibited by ouabain. The ratio of sodium ions released per one inorganic phosphate formed in the course of the reaction was found to be much higher than that established for transporting membranes of intact cells. A possible cause of this difference is discussed.     

Ionic regulation of the unicellular green algaDunaliella tertiolecta: Response to hypertonic shock

Summary The evolution of the volume, the Na⁺ and K⁺ contents and the glycerol and ATP contents were investigated after subjectingDunaliella tertiolecta cells to hypertonic shocks. It was found that the variations in the glycerol and the ion contents superimpose as the cell regulates its volume. Hypertonic shock induces a rapid increase (some minutes) in the Na⁺ influx and Na⁺ content followed by a decrease until a new steady value is reached after 30 min of cell transfer. The regulatory mechanism extruding Na⁺ out of the cells was dependent on the presence of K^– or Rb^– ions in the external medium. A transient pumping of K⁺ ions was found after subjecting the cells to a hypertonic shock. This increase in K⁺ content resulted from the transient increase in the K⁺ influxes. The K⁺ pumping mechanism was blocked by the absence of Ca⁺⁺ and Mg⁺⁺ ions in the external medium and was inhibited by DCCD, FCCP and DCMU, whereas ouabain, cyanide and PCMBS were ineffective. The increase in K⁺ content was observed if the hypertonic shock was induced by the addition of NaCl, glycerol or choline chloride. These results are interpreted on the basis of two distinct mechanisms: a Na^–/K^– exchange pump and a Na⁺ independent K⁺ pump. These ionic transfer mechanisms would participate in the osmoregulation ofDunaliella cells and would be of importance, particularly during the onset of the osmotic shock when glycerol synthesis is incomplete.