Phosphate Efflux Research Articles

Phosphate Transport in Yeast Vacuoles

The vacuole of the yeast Saccharomyces cerevisiae is a major storage compartment for phosphate. We have measured phosphate transport across the vacuolar membrane. Isolated intact vacuoles take up large amounts of added [32P]phosphate by counterflow exchange with phosphate present in the vacuoles at the time of their isolation. The bidirectional phosphate transporter has an intrinsic dissociation constant for phosphate of 0.4 mM. Exchange mediated by this carrier is faster than unidirectional efflux of phosphate from the vacuoles. The transporter is highly selective for phosphate; of other anions tested, only arsenate is also a substrate. Transport is strongly pH-dependent with increasing activity at lower pH. Similar phosphate transport behavior was observed in right-side-out vacuolar membrane vesicles.

Sediment-Water Column Coupling and the Fate of the Spring Phytoplankton Bloom in Loch Linnhe, a Scottish Fjordic Sea-loch. Sediment Processes and Sediment-Water Fluxes

Sediment-water fluxes of oxygen and nutrients before and after the impact of the spring phytoplankton bloom were measured by core incubation experiments. Less than 10 days after the bloom had settled, chlorophyll was found down to a depth of 2 cm in the sediment. This rapid burial was probably due to mixing during resuspension events. There was some increase in oxygen uptake by the sediment after settlement of the bloom and a concomitant increase in the apparent oxygen diffusion coefficient; this latter increase may indicate a stimulation of bio-irrigation. There was a nitrate influx after settlement of the bloom, but no measurable efflux of ammonium or phosphate from the sediment. There was no increase of sulphate reduction activity after the impact of the bloom nor was solid-phase extractable manganese used as an alternative terminal electron acceptor for oxidation of carbon. We conclude that much of the readily biodegradable organic components of the bloom was mineralized in the water column during sediment resuspension events.

Effects of N, N′-bisdimethyl-1,2-ethanediamine dichloride, a double-chain surfactant, on membrane-related functions in human erythrocytes

The effects of N, N′-bisdimethyl-1,2-ethanediamine dichloride (dioctyldiQAS), a double chain surfactant with two positive charges in the polar head, on the erythrocyte membrane were studied. At sublytic concentrations dioctyldiQAS protected erythrocytes against hypotonic hemolysis, induced the formation of sphero-echinocytes, increased passive fluxes of potassium through the membrane, decreased the activity of the Na +-K +-pump and decreased the efflux of phosphate. The alterations in membrane-connected functions induced by dioctyldiQAS are qualitatively similar to those induced by its single-chain close analogue decyltrimethylammonium bromide. DioctyldiQAS, however, exhibited these effects at considerably lower concentrations than decyltrimethylammonium bromide. This is most likely due to a higher extent of partitioning into the membrane by dioctyldiQAS.

Biology of polyphosphate-accumulating bacteria involved in enhanced biological phosphorus removal

Recent research on the process of biological phosphorus removal in lab-scale treatment systems has indicated that: (i) the development of an actively polyP-accumulating bacterial community after the introduction of an anaerobic period may take at least 4 months; (ii) up to 80% of all aerobic bacteria isolated from these communities are able to accumulate polyP; (iii) polyP synthesized by the bacterial communities of lab-scale treatment systems is probably mainly low polymeric, not exceeding 20 P-residues, and this polyP is rapidly degraded during the anaerobic period; (iv) the enzymatic hydrolysis of polyP under anaerobic conditions is accompanied by PHB formation from exogenous acetate, reducing equivalents are provided by the degradation of carbohydrates; and (v) nitric oxide inhibits the release of phosphate under anaerobic conditions in Renpho and F&D sludges. Bacteria belonging to the genus Acinetobacter occur in a wide variety of activated sludges in which enhanced biological phosphate removal is observed. A. johnsonii 210A was studied in detail with respect to the elemental composition of polyP granules, the enzymatic synthesis and degradation of polyP, the regulation of polyP metabolism, and the transport of phosphate. A. johnsonii 210A reflects activated sludge in a number of ways as far as polyP metabolism is concerned but its polyP is highly polymeric and the phosphate efflux rate under anaerobic conditions is relatively low and not increased by exogenous acetate. In addition to Acinetobacter, other polyP-accumulating microorganisms may be involved in biological phosphorus removal. The isolation of polyP-accumulating denitrifying bacteria may well have interesting implications for a new process design in wastewater treatment systems. Further studies on the enzymes involved in polyP biosynthesis and on the uptake and efflux systems of phosphate, potassium, magnesium and lower fatty acids in pure cultures will enlarge our insight in the energetics of the metabolism of polyP. In addition, the regulation of the metabolism of polyP-accumulating organisms needs to be studied in more detail.

Phosphate from the phosphointermediate (EP) of the human red blood cell Na/K pump is coeffluxed with Na, in the absence of external K.

This study is concerned with Na/K pump-mediated phosphate efflux that occurs during uncoupled Na efflux in human red blood cells. Uncoupled Na efflux is known to be a ouabain-sensitive mode of the Na/K pump that occurs in the absence of external Nao and Ko. Because this efflux (measured with 22Na) is also inhibited by 5 mM Nao, the efflux can be separated into a Nao-sensitive and a Nao-insensitive component. Previous work established that the Nao-sensitive efflux is actually comprised of an electroneutral coefflux of Na with cellular anions, such as SO4 (as 35SO4). The present work focuses on the Nao-insensitive component in which the principal finding is that orthophosphate (P(i)) is coeffluxed with Na in a ouabain-sensitive manner. This P(i) efflux can be seen to occur, in the absence of Ko, in both DIDS-treated intact cells and resealed red cell ghosts. This efflux of P(i) was shown to be derived directly from the pump's substrate, ATP, by the use of resealed ghosts made to contain both ATP and P(i) in which either the ATP or the P(i) were labeled with, respectively, [gamma-32P]ATP or [32P]H3PO4. (These resealed ghosts also contained Na, Mg, P(i), SO4, Ap5A, as well as an arginine kinase/creatine kinase nucleotide regenerating system for the control of ATP and ADP concentrations, and were suspended usually in (NMG)2SO4 at pH 7.4.) It was found that 32P was only coeffluxed with Na when the 32P was contained in [gamma-32P]ATP and not in [32P]H3PO4. This result implies that the 32P that is released comes from ATP via the pump's phosphointermediate (EP) without commingling with the cellular pool of P(i). Ko (as K2SO4) inhibits this 32P efflux as well as the Nao-sensitive 35SO4 efflux, with a K0.5 of 0.3-0.4 mM. The K0.5 for inhibition of P(i) efflux by Ko is not influenced by Nao, nor can Nao act as a congenor for Ko in any of the flux reactions involving Ko. The stoichiometry of Na to SO4 and Na to P(i) efflux is approximately 2:1 under circumstances where the stoichiometry of Na effluxed to ATP utilized is 3:1. From these and other results reported, it is suggested that there are two types of uncoupled Na efflux that differ from each other on the basis of their sensitivity to Nao, the source (cellular vs substrate) and kind of anion (SO4 vs P(i)) transported.(ABSTRACT TRUNCATED AT 400 WORDS)

Kinetic studies of the action of lactacin F, a bacteriocin produced by Lactobacillus johnsonii that forms poration complexes in the cytoplasmic membrane

The bacteriocin lactacin F is bactericidal against Lactobacillus delbrueckii, Lactobacillus helveticus, and Enterococcus faecalis. Activity against L. delbrueckii was recently shown to be dependent on two peptides, LafA and LafX, which are encoded within the lactacin F operon (T. R. Klaenhammer, FEMS Microbiol. Rev. 12:39-87, 1993). It has been proposed that two peptides form an active lactacin F complex. In this study, the action of lactacin F against E. faecalis ATCC 19443 and the effects of various environmental parameters were investigated in detail. Addition of lactacin F induced the loss of K+ from cells of L. delbrueckii, Lactobacillus johnsonii 88-4, and E. faecalis, while the lactacin F producer L. johnsonii VPI 11088 was not affected by the bacteriocin. Lactacin F caused an immediate loss of cellular K+, depolarization of the cytoplasmic membrane, and hydrolysis of internal ATP in E. faecalis. Lactacin F induced loss of K+ in 3,3',4',5-tetrachlorosalicylanilide-treated cells, indicating that pores are formed in the absence of a proton motive force. ATP hydrolysis was not due to dissipation of the proton motive force but was most likely caused by efflux of inorganic phosphate, resulting in a shift of the ATP hydrolysis equilibrium. Action of lactacin F was optimal at acidic pH values and was reduced in the presence of di- and trivalent cations. The lanthanide gadolinium (Gd3+) prevented action of lactacin F completely at a concentration of 0.2 mM. Lactacin F-induced loss of cell K+ was severely reduced at low temperatures, presumably as a result of increased ordering of the lipid hydrocarbon chains in the cytoplasmic membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo calcitropic effect of some vitamin D compounds in the marine Antarctic teleost, Pagothenia bernacchii

The Antarctic notothenioid, Pagothenia bernacchii, were found to have plasma total and free calcium levels, plasma inorganic phosphate and whole body calcium efflux rates which were similar to those seen in other teleosts. But total bone calcium was lower than reported for other teleosts. A single injection of vitamin D3 (5 ng g(-1) fish) increased plasma total and plasma free calcium and these increases were associated with an increase in whole body calcium efflux and bone calcification. Conversely, the same treatment with 1,25-(OH)2-D3 reduced plasma free calcium. This seco-steroid also increased the specific activity of (45)Ca in bone at 40h post-injection but did not significantly effect total bone calcium, plasma total calcium or whole body calcium efflux. 25-OH-D3 at the same dose had no effect on any of the parameters tested and none of the seco-steroids tested had any effect on plasma total inorganic phosphate. These data show that both D3 and 1,25-(OH)3-D3 can have calcitropic effects in this marine teleost and that these two forms of vitamin D can exert different effects within the same species.

Translocation of Metal phosphate via the Phosphate Inorganic Transport System of Escherichia coli

Pi transport via the phosphate inorganic transport system (Pit) of Escherichia coli was studied in natural and artificial membranes. Pi uptake via Pit is dependent on the presence of divalent cations, like Mg2+, Ca2+, Co2+, or Mn2+, which form a soluble, neutral metal phosphate (MeHPO4) complex. Pi-dependent uptake of Mg2+ and Ca2+, equimolar cotransport of Pi and Ca2+, and inhibition by Mg2+ of Ca2+ uptake in the presence of Pi, but not of Pi uptake in the presence of Ca2+, indicate that a metal phosphate complex is the transported solute. Metal phosphate is transported in symport with H+ with a mechanistic stoichiometry of 1. Pit mediates efflux and homologous exchange of metal phosphate, but not heterologous metal phosphate exchange with Pi, glycerol-3P, or glucose-6P. The metal phosphate efflux rate increased with pH, whereas the rate of metal phosphate exchange was essentially pH independent. Metal phosphate uptake was inhibited at low internal pH. Efflux was inhibited by a proton motive force (interior negative and alkaline), whereas exchange was inhibited by the membrane potential only. These results have been evaluated in terms of ordered binding and dissociation of metal phosphate and proton on the outer and inner surface of the cytoplasmic membrane.

Efflux of phosphate from the ectomycorrhizal basidiomycete Pisolithus tinctorius: general characteristics and the influence of intracellular phosphorus concentration

We have investigated phosphate absorption and efflux from mycelium of Pisolithus tinctorius and compared this with several other ecto- and ericoid mycorrhizal fungi. Phosphate absorption over a 16 h period was similar in all fungi (19–38 μmol g −1 d.w. ) with the exception of Paxillius involutus where absorption was 2–4 times greater. Efflux of phosphate from Pisolithus tinctorius followed the established pattern for efflux of ions from plant and fungal tissue. The proportion of 32 P absorbed that was lost to the bathing solution during an 8 h elution period was around 10% for all fungi. Efflux of phosphate from P. tinctorius was greatest, and absorption lowest where the fungus had a high intracellular phosphorus concentration. It is suggested that efflux of phosphate may be important in regulating mycelial phosphorus balance where mycelium has a high phosphorus status, with net efflux occurring where the intracellular orthophosphate concentration is high and the external phosphate concentration is low. The results are discussed in the context of nutrient transfer at the fungus-root interface in ectomycorrhizas.

The influence of monovalent cations on efflux of phosphate from the ectomycorrhizal basidiomycete Pisolithus tinctorius

The influence of extracellular cation concentration on efflux of phosphate from mycelium of the ectomycorrhizal basidiomycete Pisolithus tinctorus has been studied in vitro. Inclusion of K+ (or to a lesser extent Na+) in the bathing solution at concentrations in excess of 10 m m resulted in a stimulation of phosphate efflux. A similar effect was observed in two other ectomycorrhizal basidiomycetes, but in only one of three ericoid ascomycetes. The presence of Ca2+ or Ba2+ (but not Mg2+) in the bathing solution prevented the monovalent cation-stimulated efflux. Pretreatment of P. tinctorius mycelium for 8 h with up to 50 m m K+ in the absence of Ca2+ had no effect on the subsequent rate of phosphate absorption. We discuss the mechanism involved in the efflux and consider the significance of the data in relation to nutrient exchange at the fungus-root interface.

Phosphate efflux through the channels formed by colicins and phage T5 in Escherichia coli cells is responsible for the fall in cytoplasmic ATP.

Previous studies have shown that channel formation in the cytoplasmic membrane of Escherichia coli by colicin A and phage T5 leads to an efflux of cytoplasmic potassium and to a membrane depolarization. Here we show that upon opening of these channels, the intracellular ATP concentration is decreased to 10% of its original value in < 5 min. ATP is not found in the external medium, but is hydrolyzed in the cytoplasm into ADP and AMP. The rate of ATP hydrolysis depends on the number of channels and on their activity. ATP hydrolysis takes place if the F1F0-ATPase is absent or inhibited. Depolarization of the inner membrane is not the main cause of ATP hydrolysis. Opening of the phage and colicin channels also leads to an efflux of inorganic phosphate. Conditions that prevent the efflux of phosphate (i.e. depolarization of the cells and high external phosphate concentration) prevent ATP hydrolysis. We propose that ATP is hydrolyzed as a consequence of a shift in the ATP equilibrium due to the efflux of phosphate through the channels. The consequences for the cells of this ATP depletion are discussed.

Phosphate efflux from jejunal enterocytes of the rat: effect of phosphate concentration gradient and pH.

The effect of variation in the intracellular and extracellular phosphate concentration on the Pi efflux across the basolateral membrane of pre-loaded enterocytes has been examined. Efflux rate constants for Pi fell from 0.89 h-1 to 0.68 h-1 as the extracellular Pi concentration was increased from 0.5 mM to 5 mM. As the intracellular Pi concentration was raised from 0.5 to 3 mM the rate constant dropped from 0.95 h-1 to 0.77 h-1. The findings are indicative of the presence of Pi-specific transporter at the basolateral membrane. The efflux rate constant of Pi at pH 7.1 was higher than that at pH 7.4 suggesting that the Pi flux across the basolateral membrane of enterocytes follows a similar pattern towards pH changes as do fluxes across the brush-border membrane.

Phosphate uptake, efflux and deficiency in the water fern, Azolla

ABSTRACTHigh phosphorus status (High‐P) Azolla mexicana plants (P content 15.5 μmoles g fr wt−1, doubling time ca. 2.2 d) and Low‐P plants with early signs of P‐deficiency (P content 6.2 μmoles g fr wt−1, doubling time ca. 3.2 d) were used to study Pi uptake, efflux and deficiency. When High‐P plants were transferred to medium lacking Pi, uptake capacity increased 1.5‐fold within 12 h and before any detectable change in growth rate (24–48 h). When High‐P and Low‐P plants were compared, uptake rates from 0.3–10000 mmoles m−3 Pi were 2.6–1.7 times higher in Low‐P than High‐P plants (18–1150 vs 7–665 μmoles g fr wt−1 h−1). The relationship of uptake rate to concentration was interpreted as arising from a combined operation of a high‐ and a low‐affinity uptake system. Higher uptake in Low‐P plants involved a 3.4‐fold increase in Vmax (high affinity), no change in Km (high affinity), and a 1.5 to two‐fold increase in both Vmax (low affinity) and Km (low affinity). Rates of P efflux into 1–1000 mmoles m−3 Pi were 1.7 to two times higher from High‐P than Low‐P plants (12–22 vs 7–11 μmoles g fr wt−1 h−1). Below 1 mmole m−3 Pi, uptake and efflux rates were similar: the equilibrium concentration, at which net uptake was zero, was 0.22 mmoles m−3 for High‐P plants and 0.05 mmoles m−3 for Low‐P plants. Similar results were obtained with A. filiculoides. P transport characteristics of Azolla, a fern, are closely comparable with those of higher plants. Its high P requirement in the field arises from its ecological rather than physiological behaviour. We interpret the field behaviour by exploring the relationship between Azolla growth rate in the field, plant P concentration in the field, Pi transport rates required to support such growth, and Pi concentrations in pond waters. The transport characteristics which must operate in the field match those of Low‐P plants in the laboratory, not High‐P plants. Thus, Pi uptake in High‐P plants should be interpreted as repressed from the normal state, instead of that in Low‐P plants being induced.

Phosphate transport in isolated rat inner medullary collecting duct.

Phosphate transport by the inner medullary collecting duct of normal rats was studied using an in vitro microperfusion technique. Net (Jnet), lumen-to-bath (Jlb) and bath-to-lumen (Jbl) phosphate fluxes were measured using 32PO4 as tracer, in the absence of net water absorption. A net absorption of phosphate (22.3 +/- 3.3 pmol cm-2 s-1) was observed by direct determination, and was similar to the difference between the Jlb and Jbl (57.7 +/- 8.2 and 32.2 +/- 1.5 pmol cm-2 s-1 respectively). The addition of amiloride (10 microM) to the perfusate did not change the Jlb of phosphate but blocked the efflux of sodium. Also, the withdrawal of sodium from the bath and perfusion solution did not change the Jlb of phosphate. In parallel, the addition of ouabain (10 mM) to the bath fluid decreased the Jlb of sodium more (37%) than the Jlb of phosphate (12%) and did not change the Jbl of phosphate. The addition of arsenate (10 microM) to the perfusate both in the presence and in the absence of sodium caused a decrease in Jlb, but Jbl remained unchanged, and parathyroid hormone (10 U) added to the bath did not change the Jlb. The increase in pH of the bath and perfusion fluid was associated with an increase in the Jlb of phosphate, and the decrease in pH was similarly followed by a decrease in phosphate efflux. The Jbl did not change with the pH alterations. These data demonstrate that a net phosphate absorption takes place in rat inner medullary collecting duct perfused in vitro and that this transport appears to be independent of sodium absorption and the action of parathyroid hormone. Moreover, a decrease in luminal and bath pH induces a decrease in phosphate efflux.

An energy-dependent efflux system for potassium ions in yeast

An efflux of potassium ions was demonstrated in mutants of yeast cells lacking a functional high affinity carrier system for monovalent cations. This efflux showed the following characteristics: (a) It was stimulated by the presence of a substrate, either glucose or ethanol. (b) It was stimulated by several cationic organic molecules, such as ethidium bromide, dihydrostreptomycin, diethylaminoethyldextran, and also by trivalent cations, such as Al 3+ and lanthanides; this stimulation also depended on the presence of a substrate. (c) K + efflux was decreased in yeast mutants with decreased ATPase activity, which generated a lower membrane potential. (d) Although the efflux appeared to be of an electrogenic nature, producing hyperpolarization of cells, it was accompanied by the efflux of phosphate, probably as an anion partially compensating for the large amount of cations leaving the cell. (e) K + efflux was also accompanied by an uptake of protons. (f) The efflux appeared more clearly in cells grown in YPD medium, and not in more complex media nor in the same YPD medium if supplemented with Ca 2+ or Mg 2+. Efflux of monovalent cations produced by Tb 3+ and organic cationic agents was also demonstrated in wild type strains. This efflux system appears to be, at least partially, electrogenic, but seems to be also an exchange system for protons and to function as a symport with phosphate; it may be involved in the regulation of the internal pH of the cell, and appears to be regulated by its link to the energetic status of the cell, probably through the membrane potential.

Characterization of the defect in the Na(+)-phosphate transporter in vitamin D-resistant hypophosphatemic mice

Hypophosphatemic vitamin D-resistant rickets is the most common form of vitamin D-resistant rickets in man. The hypophosphatemic mouse model (Hyp) is phenotypically and biochemically similar to the human disease. Biochemically, hypophosphatemia is the hallmark of this disorder. The cause of the hypophosphatemia is thought to be secondary to a defect in the renal and/or intestinal Na(+)-phosphate transporter. The current studies were designed to investigate and characterize the localization of the defect in the Na(+)-phosphate transporter in this disorder. Phosphate uptake by renal brush border membrane vesicles (BBMV) showed a significant decrease in the slope of the initial rate of phosphate uptake in (Hyp) compared with control mice (0.009 versus 0.013, respectively). The slopes representing initial rates of phosphate uptake by jejunal BBMV were similar in (Hyp) and control mice (0.004 and 0.004, respectively). Kinetics of jejunal Na(+)-dependent phosphate uptake showed a Vmax of 0.63 +/- 0.12 and 0.64 +/- 0.12 nmol/mg protein/15 s in (Hyp) and control mice, respectively, whereas Km values were 0.12 +/- 0.08 and 0.2 +/- 0.11 mM, respectively. Similar kinetic analysis in the kidney showed a Vmax of 0.32 +/- 0.06 and 1.6 +/- 0.1 (p less than 0.01) and Km of 0.07 +/- 0.06 and 0.39 +/- 0.05 (p less than 0.02) in (Hyp) and control mice, respectively. Na(+)-dependent D-glucose uptake by BBMVs of intestine and kidney showed typical overshoot phenomena in (Hyp) and control mice. In order to explore these findings further, Na(+)-phosphate transporter expression from intestine and kidney was accomplished by microinjection of 50 ng of poly(A)+ RNA into Xenopus laevis oocytes. Na(+)-dependent phosphate uptake was expressed 6 days after the microinjection of intestinal and kidney poly(A)+ RNA from control mice. However, expression of the transporter from (Hyp) mice occurred only from the intestine, and not from the kidney. The decrease in the expression of the Na(+)-dependent phosphate transporter was not secondary to accelerated efflux of phosphate or decreased metabolism in oocytes injected with poly(A)+ RNA from (Hyp) mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential effects of triethyllead on synaptosomal [ 3H]dopamine vs. [ 3H]acetylcholine and [formula omitted] acid release

In vitro exposure to tetraethyllead (Et 4Pb, 10 μM) did not alter the release of [ 3H]dopamine (DA), [ 3H]acetylcholine (ACh), or [ 3 H]γ- aminobutyric acid (GABA) from superfused synaptosomes isolated from rat brain striatum, hippocampus, and cortex, respectively. On the other hand, a concentration-dependent increase in the spontaneous release of these transmitters was observed following exposure to triethyllead (Et 3Pb, 0.1–10 μM). The magnitude of 1 μM Et 3Pb-induced [ 3H]DA release was 5-fold greater than that observed for [ 3H]ACh or [ 3H]GABA release. Removal of [Ca 2+] e did not alter the Et 3Pb-induced increase in the release of these three transmitter substances, nor did Et 3Pb alter synaptosomal 45Ca efflux. Et ePb-induced [ 3H]ACh and [ 3H]GABA release, but not [ 3H]DA release, was blocked by lowering [Na +] e from 140 to 50 mM. Similarly, the release of [ 3H]ACh and [ 3H]GABA, but not [ 3H]DA, induced by either Na,K-ATPase inhibition or veratridine (a Na +-ionophore), was attenuated by lowering [Na +] e from 140 to 50 mM. However, Et 3Pb did not inhibit isolated synaptic membrane Na,K-ATPase, nor did the magnitude or temporal patterns of Et 3Pb-induced transmitter release resemble transmitter release induced by Na,K-ATPase inhibition. Et 3Pb and veratridine, but not Na,K-ATPase inhibition, produced an increase in synaptosomal [ 3H]deoxyglucose phosphate (dGluP) efflux, suggesting that both compounds increase membrane permeability. A Et 3Pb-induced increase in membrane permeability is further supported by electrophysiological studies using the frog neuromuscular junction in which Et 3Pb was found to reduce both the input resistance and membrane potential of muscle cells. As with [ 3H]ACh and [ 3H]GABA release, the Et 3Pb-induced increase in synaptosomal [ 3H]dGluP efflux was attenuated by lowering [Na +] e. The membrane Na + channel blocker, tetrodotoxin (TTX), delayed, but did not block, the Et 3Pb-induced increase in [ 3H]ACh release, whereas TTX blocked the release of [ 3H]ACh induced by veratridine. Unlike Et 3Pb, a differential effect of veratridine on the magnitude of [ 3H]DA release was not observed. These experiments suggest that the Et 3Pb-induced increase in [ 3H]ACh and [ 3H]GABA release is due to an increase in membrane permeability. The mechanisms underlying the differential sensitivity of [ 3H]DA release to Et 3Pb are unresolved.

Efflux of inorganic phosphate from rat hepatocytes: Lack of effect of insulin

Efflux of Pi from rat hepatocytes suspended in phosphate free-medium was studied by chemical assay of released Pi and by monitoring the loss in radioactivity of cells pre-labelled with [32P]-Pi. The release follows first-order kinetics fairly closely with a rate constant of 7 x 10(-3) min-1 approximately. Insulin at a concentration of 10(-8) M had no effect on the rate of Pi release and it is concluded therefore, that the insulin-stimulated accumulation of Pi described in the literature is the result of hormone action on Pi uptake by liver rather than on its release.

Effects of dehydroabietic acid on the erythrocyte membrane

The effects of dehydroabietic acid (DHAA), a dominant resin acid in pulp and paper mill effluents, on membrane-connected events were studied in human erythrocytes. Fifty percent haemolysis was achieved by 252 μM DHAA after 1 h of incubation at +37°C. At sublytic concentrations, DHAA protected erythrocytes against hypotonic haemolysis, with maximum protection occurring at 125 μM. In the lower range of sublytic concentrations, DHAA induced a slight echinocytosis; at higher sublytic concentrations erythrocytes were transformed to sphero-echinocytes and a release of acetylcholinesterase (exovesicles) occurred. Furthermore, at sublytic concentrations DHAA increased potassium efflux and passive potassium influx, while active potassium influx ((Na +-K +)-pump activity) and phosphate efflux were decreased. Our study indicates that DHAA acts on human erythrocytes in a way typical for amphiphilic compounds. It is proposed that DHAA by intercalating into the lipid bilayer of the membrane, affects the dynamics of the bilayer which in turn alters the permeability of the bilayer and the function of ion transporting membrane proteins.

Electrolyte and Gas Exchange During the Moulting Cycle of a Freshwater Crayfish

ABSTRACTWhole-animal net electrolyte fluxes (Ca2+, apparent H+, titratable acidic equivalents, ammonia, Na+, Cl−, K+, Mg2+, phosphate and sulphate) and respiratory gas exchange were monitored throughout the moulting cycle in juvenile freshwater crayfish Procambarus clarkii (Girard) at 21 °C. Intermoult crayfish were essentially in ion balance. As crayfish approached ecdysis (–3 days, where t=0 is the day when the cuticle is shed), there was a net efflux of Ca2+ (–1000μmol kg−1 h−1) correlated with a corresponding uptake of acidic equivalents (or base output) of +2000 μmol kg−1 h−1. Following ecdysis, both fluxes switched vector; uptake of Ca2+ (+2000/mol kg−1 h−1) and basic equivalents (+4000μmol kg−1 h−1) were completed within 6 days. The moulting cycle also affected fluxes of electrolytes other than those involved in CaCO3 resorption and deposition. Crayfish remained in Na+ and Cl− balance from intermoult up to ecdysis. Following ecdysis, both were taken up actively at rates of around +500μmol kg−1 h−1 for 3 days, presumably restoring the haemodilution that would have resulted from water loading. A premoult efflux of K+ was partially offset by postmoult uptake. Meanwhile, crayfish experienced increased efflux of phosphate following ecdysis, probably because of increased integumentary permeability. Rates of O2 uptake and CO2 excretion increased to peak values (double intermoult rates) immediately prior to ecdysis. While recovered during postmoult, dropped precipitously, significantly reducing the gas exchange ratio. Since the deficit agreed well with the postmoult basic equivalent uptake, the latter is probably attributable to HCO3− uptake for calcification.