Exclusion of charged macromolecules in the pulmonary interstitium

The polyanionic glycosaminoglycans and glycoproteins of the interstitial ground substance could influence the interstitial distribution volumes (VA) of plasma proteins filtered across the pulmonary capillaries depending upon the molecular charge of the proteins. To determine if such differences occur, two isozymes of lactate dehydrogenase (LDH) were selectively labeled with either 125I or 131I and infused simultaneously at a rate sufficient to maintain constant plasma concentrations for 24 hr. The isoelectric points of LDH 1 and LDH 5 are 5.0 and 7.9, respectively, but they have the same mol wt (140,000) and hydrodynamic radius (42 A). VA values were calculated in lymph equivalents based on the respective activities in prenodal tracheobronchial lymph. We corrected the residual blood in the tissue using either 99mTc-labeled red cells or Dextran 70 washout of blood. At 24 hr the VA for cationic LDH 5 was significantly greater than that of anionic LDH 1 (0.299 vs 0.197 ml/g wet wt) in the lung. Lymph/plasma ratios for LDH 1 and 5 were not significantly different (0.63 vs 0.58) and total extravascular lung water was not significantly different from normal. This indicates the LDH 1 was excluded from a significantly greater portion (47%) of interstitial fluid than LDH 5 (21%), and suggests an interaction of the fixed negative charges on interstitial polysaccharides with cationic proteins.

Biochemical and functional changes in hearts from rabbits with diabetes

Biochemical and myocardial functional changes were determined in rabbits made diabetic with alloxan (100 mg/kg, intravenously, two injections 24 h apart). Alloxan-induced diabetes was characterized by a state of hypoinsulinaemia and hyperglycaemia. After 10 weeks of diabetes, significant decreases in heart and left ventricular weights as well as increased serum and heart triglycerides and cholesterol were observed in the diabetic animals (p less than 0.05). In addition, left ventricular pressure, heart rate and rate of left ventricular pressure development were all decreased in the animals. The diabetic state was also associated with a slight elevation in myocardial calcium and a significant decrease in magnesium levels (p less than 0.05). Subcellular fractionation of diabetic hearts indicated the presence of alterations in myofibrillar and sarcoplasmic reticulum marker enzymes (p less than 0.05). Among the lysosomal enzymes, measured, N-acetyl-beta-glucosaminidase activity was significantly increased in the homogenates of diabetic left ventricles (p less than 0.05). These alterations in hearts of diabetic rabbits may be responsible for some aspects of diabetic cardiomyopathy.

Studies of the limited degradation of mucus glycoproteins. The mechanism of the peroxide reaction

The reaction between ovarian-cyst glycoproteins and H2O2 was investigated in the presence of a number of inhibitors and catalysts. Azide and 2H2O were separately found to have little effect, implying that singlet oxygen was not involved. Superoxide dismutase was destroyed by H2O2, but mannitol had no effect: thus generalized attack by OH., whether originating from HO2.- or more directly, is not indicated. The glycoproteins contained trace quantities of Cu and Fe, amounting to about 2 atoms of metal per glycoprotein molecule. Treatment of the glycoproteins with the strong chelator DETAPAC (diethylenetriaminepenta-acetic acid) or Chelex resin eliminated the reaction with H2O2; activity could be restored by addition of Cu2+ or Fe2+ in millimolar quantities. It was concluded that metal-ion catalysis is an essential step in the attack of H2O2 on glycoproteins. Spectroscopic and other evidence showed that Cu2+ (and probably Fe2+) complexes strongly with poly-L-histidine, and implies that the Cu2+ or Fe2+ in the glycoproteins is complexed with some of the histidine residues in the glycosylated backbone. Neither polyhistidine nor polyproline reacted with H2O2 in the absence of metal ions, but small quantities of Cu2+ or Fe3+ caused degradation. This was rapid with polyhistidine, which was converted largely into aspartic acid, but slower with polyproline, where limited conversion into glutamic acid occurs. These findings confirm the original hypothesis that peroxide attack on glycoproteins occurs largely at the histidine residues, with simultaneous peptidolysis. The mechanism most probably involves the liberation of OH. by an oxidation-reduction cycle involving, e.g. Cu+/Cu2+: specificity of attack at histidine is due to the location of the metal at these residues only.

Mitochondrial granules: are they reliable markers for heavy metal cations?

Mitochondrial granules have been used as markers for heavy metal cations, but since such granules can also be found in tissues in the absence of such cations, an attempt was made to define conditions under which these different granules might be visualised. The tissue used was the smooth muscle of the central ear artery of the rabbit. In all studies, the presence or absence of mitochondrial granules was determined by several observers, using coded specimens so that the previous treatment of the specimens was not at the time known to the observers. Paired tissues were exposed for 30 or 90 minutes at 20, 30 or 39 degrees C to an incubate containing either 10 mmol/l barium or a control barium-free solution. After fixation in osmium tetroxide, there was no difference between the two groups; in both cases granules appeared more frequently the longer the time and the higher the temperature of incubation. In a further series where glutaraldehyde was the fixative, granules were identified in 23 out of 41 tissues incubated with barium, but in only 1 out of 41 control tissues (P less than 0.001). Electron probe microanalysis showed that granules in osmium-fixed tissues contained osmium as the main element, whereas granules in glutaraldehyde-fixed tissues which had been incubated with barium showed barium as the predominant cation. Thus mitochondrial granules can be reliable markers for heavy metal cations, but only under carefully controlled conditions.

X-ray micro analyses of cations (Na, K, Ca) and anions (S, P, Cl) in uterine secretions during blastocyst implantation in the rat

The mass changes of sodium, potassium, and calcium ions in the rat uterine secretion at blastocyst delay, activation, and attachment have been estimated with X-ray microanalyses of samples of uterine secretions absorbed by small Sephadex beads. A quantification of the ions was attempted by using a standardized coat of gold on the beads as a reference element for normalization of the ion peaks and by fitting the normalized values into corresponding linear regression equations obtained from measurements of step-wise dilutions of a control rat serum. The concentrations of sodium observed at delay, activation, and attachment were 117, 201, and 203 mEq/l, respectively, and those of potassium were 6, 18, and 19 mEq/l, respectively. Calcium values were about 2 mEq/l and decreased at attachment. Among the anions, only the chloride concentration increased at activation and attachment.

Electroneutral transport of organic cations in canine renal brush border membrane vesicles (BBMV)

The effect of potential difference on the organic cation/H+ antiport system located in brush border membrane vesicles was examined. Potential difference was generated using K+ gradients and a K+-specific ionophore, valinomycin. Transport of a prototypic organic cation, 1N-[3H]methylnicotinamide (NMN), was assessed under conditions where K+ diffusion potentials generated transient intravesicular negative and positive states. The results demonstrate that NMN transport is independent of potential difference. The organic cation/H+ coupling ratio was studied by imposing transmembrane H+ and NMN gradients of varying magnitudes and measuring net flux of NMN for a 5-sec period. Consistent with an equilibrium thermodynamics model, no net NMN flux is observed when the NMN gradient from out to in is equal to the H+ gradient from out to in ([NMN]o/[NMN]i equals [H+]o/[H+]i). This suggests that the carrier is at equilibrium and that the stoichiometry for the organic cation/H+ antiport is 1:1.

Administration of atrial natriuretic factor inhibits sodium-coupled transport in proximal tubules

The newly discovered peptides extracted from cardiac atria, atrial natriuretic factors (ANFs), when administered parenterally cause renal hemodynamic changes and natriuresis. The nephron sites and cellular mechanism accounting for profound increase in Na+ excretion in response to ANFs are not yet clarified. In the present study we investigated whether synthetic ANF peptide alters the reabsorption of Na+ and reabsorption of solutes cotransported with Na+ in the proximal tubules of rats. Synthetic ANF peptide consisting of 26 amino acids, 4 micrograms/kg body wt/h, or vehicle in controls, was infused to surgically thyroparathyroidectomized anesthetized rats. After determination of the fractional excretion (FE) of electrolytes (Na+, K+, Pi, Ca2+, Mg2+, HCO3), the kidneys were removed and luminal brush border membrane vesicles (BBMVs) were prepared from renal cortex. Solute transport was measured in BBMVs by rapid filtration techniques. Infusion of ANF peptide increased FENa, FEPi, and FEHCO3; but FECa, FEK, and FEMg were not changed. The increase in FENa was significantly correlated, on the one hand, with increase of FEPi (r = 0.9, n = 7; P less than 0.01) and with increase of FEHCO3 (r = 0.89, n = 7; P less than 0.01). On the other hand, FENa did not correlate with FEK, FECa, or with FEMg. The Na+ gradient-dependent uptake of Pi by BBMVs prepared from renal cortex of rats receiving ANF infusion was significantly (P less than 0.05) decreased (-25%), whereas the Na+ gradient-dependent uptake of L-[3H]proline and of D-[3H]glucose or the diffusional uptake of 22Na+ were not changed. ANF-elicited change in FEPi showed a close inverse correlation with decrease of Na+-dependent Pi uptake by BBMVs isolated from infused rats (r = 0.99, n = 7; P less than 0.001). Direct addition of ANF to BBMVs in vitro did not change the Na+ gradient-dependent Pi uptake. In rats infused with ANF, the rate of amiloride-sensitive Na+-H+ exchange across the brush border membrane (BBM) was significantly (P less than 0.05) decreased (-40%), whereas the diffusional 22Na+ uptake (0.5 min) and the equilibrium (120 min) uptake of 22Na+ were not changed. The inhibition of Na+-H+ exchange after ANF was likely due to alteration of the BBM antiporter itself, in that the H+ conductance of BBMVs was not increased. We conclude that synthetic ANF (a) decreases tubular Na+ reabsorption linked to reabsorption of HCO3 in proximal tubules, and (b) inhibits proximal tubular reabsorption of Pi coupled to Na+ reabsorption, independent of secretion and/or action of parathyroid hormone or calcitonin. These ANF effects are associated with inhibition of Na+-Pi synport and of Na+-H+ antiport in luminal BBMs. Our findings document that inhibition of Na+-coupled transport processes in proximal tubules is an integral part of the renal response to ANF.

The role of the Na+/H+ exchange system in the regulation of the internal pH in cultured cardiac cells

The Na+/H+ exchange system is not the major mechanism that regulates the internal pH value (pHi) of chick cardiac cells in culture under normal physiological conditions in the absence of carbonate. In cardiac cells in which the internal pH has been lowered to 6.6-6.7, the Na+/H+ exchanger becomes the major mechanism to bring back pHi to normal values (pHi = 7.3). The blockade of the Na+/H+ exchange activity with an active amiloride derivative, ethylisopropylamiloride, prevents internal pH recovery. The internal pH dependence of the Na+/H+ exchanger activity has been carefully studied. The [H+]i-dependence is very cooperative. For an external pH of 7.4, the system is nearly completely inactive at pHi 7.8 and nearly completely active at pHi 6.9-7.0 with half-maximum activation at pHi = 7.35. The increased activity of the Na+/H+ exchange system which follows the acidification of the internal medium produces an activation of the (Na+,K+)-ATPase.

Ion dependence of the Bacillus subtilis RNase P reaction

The properties of the Bacillus subtilis RNase P are characterized with regard to the types and concentrations of monovalent and divalent ions required to potentiate precursor tRNA cleavage by the protein-RNA holoenzyme and the catalytic RNA alone. The ionic dependence of the RNase P RNA-catalyzed reaction in part seems due to a requirement for ion shielding between substrate and catalytic RNAs. The RNase P protein, which binds to RNA nonspecifically and tightly, likely serves, in part, as a cation screen. However, the character of the ion dependence of the RNA catalysis, the inhibition by high SO2-4 concentration, and potentiation by solvents suggest that RNA conformational transition may be involved in the reaction. It is proposed that the reason for catalysis by RNA in the RNase P reaction may be a requirement for fluidity in the structure of the catalyst, so that it can accommodate many tRNA substrates, which vary in their structural details.

Comparative structural aspects of cation binding to phosphatidylserine bilayers

X-ray diffraction data recorded for monovalent and divalent cation complexes of a series of phosphatidylserines (PS) varying in chain length reveal a simple structural pattern. Only two bilayer structural types differing in hydrocarbon chain tilt but with similar polar group conformations are observed for (i) anhydrous acidic PS, (ii) anhydrous K+-PS, and (iii) Li+, Mg2+, Ca2+, Sr2+, Ba2+, and Pr3+ complexes of 'hydrated' PS. The X-ray diffraction data suggest that PS becomes dehydrated on complexing with Li+, Mg2+, Ca2+, and other divalent cations and adopts either the chain untilted (form I) or tilted (form II) bilayer structure.

Electrochemical profile of K+ and Na+ in the amphibian early distal tubule

Double-barreled microelectrodes selective to either potassium or sodium were used to determine the transepithelial potential difference (VTE) and the intraluminal activity of potassium (alpha LuK) or sodium (alpha LuNa) in the early distal tubule (EDT) of Triturus waltlii in vivo; luminal activities were compared with the corresponding plasma ion activities, alpha PtK and alpha PtNa. The transepithelial equilibrium potentials for potassium (EK(TE] and sodium (ENa(TE] were computed from the respective transmural chemical distributions: they were used to assess the transepithelial electrochemical potential differences [(V-EK)TE and (V-ENa)TE]. By dividing the raw data into three groups of 30% total tubular length (0-30, 31-60, 61-90%), the following results were obtained. 1) VTE increases from +15 to +20 mV (lumen positive) between the first and second portion of the EDT but remains constant thereafter. 2) The alpha LuK/alpha PtK ratio decreases steadily along the EDT from 1.92 to 1.66 and then to 1.32. 3) The values of alpha LuNa/alpha PtNa in the same three subdivisions are 0.79, 0.44, and 0.45. 4) The (V-EK)TE difference is largely positive along the whole EDT: +32, +33, and +27 mV. 5) The (V-ENa)TE difference declines from +9 mV (first portion) to values statistically not different from zero in the last two thirds of the EDT.(ABSTRACT TRUNCATED AT 250 WORDS)

Prooxidant states and tumor promotion

There is convincing evidence that cellular prooxidant states--that is, increased concentrations of active oxygen and organic peroxides and radicals--can promote initiated cells to neoplastic growth. Prooxidant states can be caused by different classes of agents, including hyperbaric oxygen, radiation, xenobiotic metabolites and Fenton-type reagents, modulators of the cytochrome P-450 electron-transport chain, peroxisome proliferators, inhibitors of the antioxidant defense, and membrane-active agents. Many of these agents are promoters or complete carcinogens. They cause chromosomal damage by indirect action, but the role of this damage in carcinogenesis remains unclear. Prooxidant states can be prevented or suppressed by the enzymes of the cellular antioxidant defense and low molecular weight scavenger molecules, and many antioxidants are antipromoters and anticarcinogens. Finally, prooxidant states may modulate the expression of a family of prooxidant genes, which are related to cell growth and differentiation, by inducing alterations in DNA structure or by epigenetic mechanisms, for example, by polyadenosine diphosphate-ribosylation of chromosomal proteins.

Studies on cataractogenesis in humans and in rats with alloxan-induced diabetes. I. Cation transport and sodium-potassium-dependent ATPase

Changes in the cation balance cause hydration and initiate the process of lens opacification. Such alterations were studied in human cataractous lenses and during the development of alloxan-induced diabetic cataract in rats by biochemical and histochemical techniques. The development of alloxan-induced cataract in rats was examined in vivo which showed cortical opacities beginning after 32 days. These opacities did progress to maturity after 64 days and finally the lenses were completely opacified after 96 days of alloxan treatment. The histochemical localization of sodium-potassium-activated adenosine triphosphatase using three different methods provided information on the possible role of this enzyme in normal and cataractous lenses. In human cataractous lenses, sodium-potassium adenosine triphosphatase activity was found to be considerably decreased, whereas no activity of this enzyme was localized in human diabetic cataractous lenses. An animal model provided evidence that an apparent decrease of sodium-potassium adenosine triphosphatase may be involved in the initiation of alloxan-induced diabetic cataract in rats.

Passive cation permeability of turtle colon: evidence for a negative interaction between intracellular sodium and apical sodium permeability

The role of intracellular sodium in the regulation of apical sodium permeability was investigated in an electrically "tight" epithelium, the turtle colon. In the presence of low mucosal sodium (3 mM) and serosal ouabain, an inhibitor of the basolateral sodium pump, the apical membrane retained a substantial amiloride-sensitive, sodium conductance and the basolateral membrane exhibited a barium-sensitive potassium conductance in parallel with a significant sodium (and lithium) conductance. In the presence of a high mucosal sodium concentration (114 mM), however, inhibition of active sodium absorption by ouabain led to a disappearance of the amiloride-sensitive, transepithelial conductance that was due, at least in part, to a virtual abolition of the apical sodium permeability. Two lines of evidence indicate that this permeability decrease was dependent upon an increase in intracellular sodium content. First, raising the mucosal sodium concentration from 3-114 mM in the presence of ouabain reversibly inhibited the amiloride-sensitive conductance. The time course of the decline in conductance paralleled the apparent intracellular accumulation of sodium in exchange for potassium, which was monitored as a transient deflection in the amiloride-sensitive, short-circuit current. Second, the inhibitory effect of mucosal sodium-addition was markedly attenuated by serosal barium, which prevented the accumulation of sodium by blocking the electrically coupled, basolateral potassium exit. These results support the notion of a "negative feedback" effect of intracellular sodium on the apical sodium permeability.

Erythrocyte cation fluxes in essential hypertension of children and adolescents

The maximal rate of ouabain sensitive Na+ (pump), the maximal rate of Na+ and K+ furosemide (co-transport), the maximal rate of Na+ lithium countertransport and the rate constant of Na+ and K+ passive permeability were determined in the following population: 27 controls, 39 labile essential hypertensive, 10 stable hypertensive children, 6 normotensive offspring of hypertensive parent (s), and 19 hypertensive secondary to renal disease. The normal values for children were determined for all these various fluxes. When a rigid technique was applied and particularly when the post loading concentration of intracellular Na+ was determined and when the cells were not swollen by Na+ loading, the technique was reliable, reproducible and our results could be compared with the results found in adults by researchers using the same rigid technical criteria. In labile hypertension, 21% of adolescents had a decreased co-transport, 17% an increased countertransport and 6% an increased Na+ leak. In stable hypertension none had a decreased co-transport, 29% had an increased countertransport and 25% had an increased Na+ leak. Moreover, plasma norepinephrine was elevated in most of the patients presenting a decreased co-transport. Our results suggest that adolescents with labile essential hypertension and elevated plasma norepinephrine present with a decreased co-transport whereas adolescents with stable essential hypertension and normal or subnormal plasma norepinephrine present with an increased countertransport.

Charged amphiphiles regulate heart contractility and sarcolemma-Ca2+ interactions

We have used charged amphiphiles as phospholipid analogues to modulate the interaction of Ca2+ with myocardial sarcolemma. The amphiphiles were dodecyl sulfate, dodecyltrimethylamine, and lauryl acetate; these are anionic, cationic, and neutral molecules, respectively. The hydrophobic alkyl chain is identical in each case; only the hydrophilic head group is varied. The anionic dodecyl sulfate (50-100 microM) augmented the Ca2+ binding and Na+-Ca2+ exchange activity of sarcolemmal vesicles by approximately 80% and increases the contractility of rabbit papillary muscle. Both developed force and its derivative were increased by approximately 100% with no increase in rest tension. Cationic dodecyltrimethylamine (20-100 microM) produced nearly opposite effects. Neutral lauryl acetate (100 microM) had little apparent effect on any measurement. The charged amphiphiles should be useful tools for further elucidation of excitation-contraction coupling processes in a variety of contractile tissues.

15N electron nuclear double resonance of the primary donor cation radical P+.865 in reaction centers of Rhodopseudomonas sphaeroides: additional evidence for the dimer model

Four 15N hyperfine coupling constants, including signs, have been measured by electron nuclear double resonance (ENDOR) and electron nuclear nuclear triple resonance (TRIPLE) for the bacteriochlorophyll a radical cation, BChla+., in vitro and for the light-induced primary donor radical cation, P+.865, in reaction centers of Rhodopseudomonas sphaeroides R-26. A comparison of the data shows that the hyperfine coupling constants have the same sign in both radicals and are, on the average, smaller by a factor of 2 in P+.865. These results provide additional evidence that P+.865 is a bacteriochlorophyll dimer and are in contradiction with the monomer structure of P+.865 recently proposed by O'Malley and Babcock. The reduction factors of the individual 15N couplings, together with the evidence from proton ENDOR data and molecular orbital calculations, indicate a dimer structure in which only two rings (either I and I or III and III) of the bacteriochlorophyll macrocycles overlap.

Rapid purification of a phospholipase-free alpha-bungarotoxin: maintenance of cation barriers of acetylcholine receptor membranes upon preincubation with purified toxin

The purification of highly homogeneous, phospholipase-free alpha-bungarotoxin (alpha-Bgt) from the venom of the elapid Bungarus multicinctus or from commercial samples of alpha-Bgt is described. The method combines a conventional procedure for the purification of alpha-Bgt [D. Mebs, K. Narita, S. Iwanaga, Y. Samejima, and C. Y. Lee (1972) Hoppe-Seyler's Z. Physiol. Chem. 353, 243-262] with high-resolution gel-filtration and cation-exchange chromatography steps to remove membrane-damaging, contaminating phospholipase activity. The procedure also removes contaminating radioactive peptides from commercial preparations of 125I-alpha-Bgt. Apparent homogeneity of the purified alpha-Bgt (referred to as fraction D in the text), as well as the absence of contaminating phospholipase A2 activity, is assessed by (i) polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, (ii) gel-filtration and cation-exchange high-performance liquid chromatography, (iii) direct measurements of phospholipase A2 activity under conditions where very low enzymatic levels should be detected, (iv) lack of interference with the passive cation permeability properties of acetylcholine receptor membranes, (v) competitive inhibition of 125I-alpha-Bgt binding to the acetylcholine receptor membranes, and (vi) amino acid analysis and end-group (C- and N-terminus) determination. alpha-Bgt preparations subjected to these criteria do not exert the increase in membrane passive permeability to cations detected with other laboratory or commercial samples of alpha-Bgt. Availability of the new alpha-Bgt preparation allows for an assessment of the inertness of alpha-Bgt on lipid membrane properties while preventing cholinergic ligand binding to nicotinic acetylcholine receptor-rich membranes. These conditions are necessary for experiments requiring maintenance of the physical and phospholipid integrity of membranes.

Does calcium couple the apical and basolateral membrane permeabilities in epithelia?

Tight epithelial cells actively transport sodium against steep electrochemical gradients. To maintain a constant internal ionic content and volume, they must continuously adjust the passive cation permeabilities of their membranes as the rate of transport varies. There is evidence suggesting that changes in cell calcium may accomplish this task. An increase in cell calcium reduces the luminal sodium permeability and increases basolateral potassium permeability. There is basolateral sodium-calcium exchange through which changes in the rate of sodium transport, reflected in the cell sodium activity, are translated into changes in cell calcium. To demonstrate that cell calcium couples the permeability of the cell membrane requires obtaining measurements of cell calcium activity under physiologically relevant conditions, and, to date, there are no measurements during spontaneous changes in the rate of transport. However, there are measurements following ouabain inhibition of the pump indicating that the increase is sufficient to account for the reduction in luminal sodium permeability observed in intact tissues.

Lead accumulation by rat renal brush border membrane vesicles

Pb++ accumulation by rat renal cortical brush border membrane vesicles was evaluated by in vitro incubation with rapid filtration technique. Pb++ uptake was time- and concentration-dependent, with apparent saturation of binding sites at 100 to 200 microM (5 sec initial rate experiments). Equilibrium binding studies (60-min incubation) showed that the ratio of bound Pb++ to free Pb++ was constant at 1.25 +/- 0.07 between 0.01 to 10 microM Pb, with decreasing bound to free ratios at higher concentrations. Osmotic experiments showed that Pb++ uptake was due primarily to membrane binding rather than intravesicular accumulation. Electrochemical gradients of NaCl, KCl or protons did not increase vesicle uptake of Pb++. Incubation of vesicles with a number of amino acids did not stimulate Pb++ uptake although two (cysteine and glutathione) and the chelators EDTA or ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid) completely blocked this process. Competition studies with a number of other metals (at 10 microM and 1 mM) showed that only Sn++ or Sn +, La , Fe++ or Fe and Cu++ produced significant reductions in Pb++ uptake whereas Mg++, Ca++, Zn++, Cd++ and Hg++ were without effect on this process. Release of 203Pb from preloaded vesicles was accelerated in the presence of either cysteine or Sn +. Prior in vivo exposure to Pb (3 mg of Pb/kg i.v.) reduced Pb uptake to 70% of that of vesicles prepared from control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorylation of the transferrin receptor in isolated sheep reticulocyte plasma membranes

The transferrin receptor of sheep reticulocyte plasma membranes undergoes phosphorylation with [gamma-32P]ATP in isolated plasma membranes. The phosphorylation is stimulated by Mn2+, Co2+, and Mg2+, but not by Ca2+, Ba2+, Zn2+, Fe2+, or Cu2+. There is no detectable effect of cyclic nucleotides on the phosphorylation of the receptor. Transferrin and a monoclonal antibody against the transferrin receptor have no apparent effect on receptor phosphorylation in intact cells or isolated membranes. Immunoprecipitates of the receptor retain ability to phosphorylate the receptor. The phosphorylation appears to be at a serine residue which turns over with a half time of 20-30 min. ATP appears to be the best, but not the only substrate for receptor phosphorylation.

Patch-clamp study of rubidium and potassium conductances in single cation channels from mammalian exocrine acini

Single-channel current recordings were carried out on excised inside-out patches of baso-lateral plasma membrane from exocrine acinar cells. The mouse pancreas and submandibular gland as well as the pig pancreas were investigated. In the mouse pancreas the voltage-insensitive Ca2+-activated cation channel was studied. Single-channel current-voltage (i/v) relationships were studied in symmetrical Rb+-rich solutions and in asymmetrical Rb+/Na+ and Na+/Rb+ solutions. In all cases the i/v relations were linear and had the same slope representing a single-channel conductance of about 33 pS which is identical to that previously obtained with symmetrical Na+ solutions or asymmetrical Na+/K+ solutions. In the mouse submandibular gland and the pig pancreas the voltage and Ca2+-activated K+ channel was studied. The outward currents observed after depolarization in the presence of quasi-physiological Na+/K+ gradients were immediately abolished when all the K+ in the bath fluid was replaced by Rb+ (bath fluid in contact with inside of plasma membrane). This effect was immediately and fully reversible upon return to the high K+ solution. The voltage and Ca2+-activated K+ channel was also studied in asymmetrical K+/Rb+ and Rb+/K+ solutions. In the first case inward (K+) currents could be observed but not outward (Rb+) currents, while in the other case inward (Rb+) currents could not be seen whereas outward (K+) currents were measured. The current-voltage relationships were approximately linear and the null potential was close to 0 mV in both situations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of size of Trichinella spiralis (Nematode) infections on glucose and ion transport in the rat intestine

An in vivo perfusion technique, using 3 intestinal loops representing the anterior, mid and posterior regions of the rat small intestine, was used to determine intestinal glucose uptake 5 days after infection with Trichinella spiralis. At high levels of infection (3,000 and 6,000 larvae/rat) net glucose absorption by the intestinal mucosa was significantly impaired in all regions of the small intestine when compared to uninfected controls. At low levels of infection (50 larvae/rat) glucose uptake by the mucosa was significantly enhanced in all 3 regions of the small intestine. Intermediate levels of infections (200-1,000 larvae/rat) also enhanced glucose uptake, but only in the anterior regions of the small intestine. When washings from the small intestine of rats infected with 50 larvae/rat were added to the perfusion fluid used on uninfected rats, glucose uptake was also significantly enhanced. These results suggest that at low levels of infection the intestinal lumen contains a metabolite which may affect the mucosal transport of glucose and the related fluxes of H2O, Na+, Cl-, and K+, in the rat intestine. Luminal [H+] and pCO2 decreased from the proximal to distal regions of the small intestine following perfusion; pO2 was significantly decreased in the proximal and distal regions.

Interactions of calcium and other metal ions with caldolysin, the thermostable proteinase from Thermus aquaticus strain T351

Caldolysin, the extracellular proteinase from the extreme thermophile Thermus aquaticus strain T351, is stabilized by Ca2+. A variety of metal ions were able to substitute for Ca2+. Most were unable to confer as much stability as Ca2+, with the exception of the lanthanide ions, which increased the half-life at 95 degrees C from 1 h to more than 4 h. Results from a variety of separation methods indicated that caldolysin binds 6 Ca2+ ions/molecule of enzyme. The presence of non-linear Ca2+ titration plots, and the removal of 4 Ca2+ ions/molecule by treatment with a cationic ion-exchange gel suggested that caldolysin possesses at least two different types of Ca2+-binding sites, with different affinities. Average binding constants of the two types of binding sites were 2.8 X 10(4)M-1 (for the low-affinity sites) and 7.5 X 10(5) M-1 (for the high-affinity sites). The total Ca2+-binding free energy for caldolysin was shown to be greater than for either thermolysin or Bacillus subtilis neutral proteinase. It appears that the higher thermostability of caldolysin is due to the presence of 6 Ca2+ ions rather than 4 Ca2+ ions/molecule.

Effects of enantiomers of indacrinone (MK-196) on cation transport by the loop of Henle and distal tubule studied by microperfusion in vivo

We have studied the effects of the two enantiomeric forms of the diuretic agent, indacrinone (MK-196), upon transport of sodium and potassium by the loop of Henle and distal tubule, using the technique of continuous microperfusion, in vivo, of individual tubular segments in the rat kidney. In the loop of Henle, both the (+)-and (-)-enantiomers, when included in the tubular perfusion fluid at a concentration of 5 X 10(-4) M, inhibited the reabsorption of sodium and potassium, but the (-)-enantiomer was significantly more effective in this regard than the (+)-enantiomer. Although loop sodium reabsorption was incompletely blocked by either form of the drug, potassium reabsorption by the loop was on average abolished by (-)-MK-196 and was actually converted in some experiments to an appreciable net secretory flux. In the distal tubule, both enantiomers inhibited net sodium reabsorption, but neither affected the control level of potassium secretion. These experiments provide direct evidence that the natriuretic effect of this agent is due to actions on sodium transporting sites in the loop of Henle and distal tubule. Furthermore, because potassium transport was affected only in the loop, they suggest that the nature of the cellular cation transport mechanism influenced by the drug may be different at the two nephron sites studied.

Implications of the immunohistochemical localization of the carbonic anhydrase isozymes for their function in normal and pathologic cells

Histochemical knowledge of the distribution of CA and the two isozymes CA I and CA II has been reviewed here. An abundance of CA occurs most commonly in epithelial cells specializing in transport of ions and water. A mechanism is favored whereby the polarity of efflux of CA-generated protons and bicarbonate across the apical versus the basolateral plasmalemma depends not on the location of CA, which is probably in the cytosol in most sites, but rather on the transport properties of the luminal compared with the serosal region of the plasma membrane in each epithelial cell type. CA exists also in some protein-secreting, merocrine cells including serous cells of salivary and tracheobronchial glands. Available evidence supports the possibility that CA stored as a secretory product in the cytoplasmic granules is released from these cells and, thus, implies extracellular biologic activity for CA in these sites. CA exists also in abundance in various nonepithelial cells performing different and not fully defined biologic functions in these cells. Prevalence of one isozyme over another varies in different cell types. A question remains whether the significance of this variability depends on work load or other undetermined factors.

Ultrastructural localization of anionic and cationic ferritin in the rat glomerular basement membrane in protein-overload proteinuria

The penetration into the glomerular basement membrane of anionic and cationic ferritin has been studied in rats made proteinuric by intraperitoneal administration of bovine serum albumin. In comparison with control animals anionic ferritin penetrated the glomerular basement membrane to a much greater extent in proteinuric rats. Some ferritin particles were observed in small invaginations of the epithelial cell membrane adjacent to the glomerular basement membrane and incorporated in pinocytotic vesicles within the epithelial cell cytoplasm. This was not seen in control animals. Cationic ferritin distribution in the glomerular basement membrane was similar in control and proteinuric rats suggesting that the increased anionic ferritin penetration observed occurs without any reduction in fixed anionic charge.

Cellular basis for arrhythmogenicity of ionophores with different cation selectivities

In high concentrations, the ionophores salinomycin, monensin and X-537A cause cardiac arrhythmias in vivo. To determine if these arrhythmias result from a direct action of these ionophores on cardiac electrophysiology, we studied their effects on automaticity and transmembrane action potentials of isolated canine left ventricular Purkinje fibers. High concentrations of the ionophores suppressed automaticity and shortened action potential duration. These data suggest that high concentrations of the ionophores provoke cardiac arrhythmias in vivo by similar mechanisms despite their diverse cation transport selectivities.

[Elimination of organic cations from the eye]

Substances injected into the vitreous cavity leave the eye partly by diffusion into the flowing aqueous, but sometimes also by other mechanisms. To look for such other mechanisms removing organic cations from the rabbit eye, 5 labeled quaternary ammonium compounds were injected intravitreally, mixed with labeled sucrose. The latter leaves essentially by way of the aqueous only. After predetermined times had elapsed the rabbits were killed, and the radioactivity remaining in each eye was measured after combustion of the dried eye bulb. The anticholinergic drug Emepronium disappeared faster than sucrose but only after a delay of many hours. The main experiments were therefore concerned with the time interval 24-48 h after injection. The N- hexylhomologue of Emepronium ' Cetihex ' and the non-sedative antihistamine Aprobit were not eliminated faster than sucrose during this time interval. Since the molecular weights of these quaternaries are similar to that of sucrose and their free diffusion rate should be similar, the present experiments over a limited time interval have proved the existence of an elimination mechanism (besides aqueous flow) only for Emepronium. Tetramethylammonium and tetraethylammonium disappeared markedly faster than sucrose. Since there is no satisfactory way to take their much lower molecular weight into account, the question of a special system for these cations remains open.

Pulmonary and generalized lysosomal storage induced by amphiphilic drugs

Administration of amphiphilic drugs to experimental animals causes formation of myelinoid bodies in many cell types, accumulation of foamy macrophages in pulmonary alveoli and pulmonary alveolar proteinosis. These changes are the result of an interaction between the drugs and phospholipids which leads to an alteration in physicochemical properties of the phospholipids. Impairment of the digestion of altered pulmonary secretions in phagosomes of macrophages results in accumulation of foam cells in pulmonary alveoli. Impairment of the metabolism of altered phospholipids removed by autophagy induces an accumulation of myelinoid bodies. The administration of amphiphilic compounds thus causes pulmonary intra-alveolar histiocytosis which is a part of a drug-induced lysosomal storage or generalized lipidosis. The accumulation of drug-lipid complexes in myelinoid bodies and in pulmonary foam cells may lead to alteration of cellular functioning and to clinical disease. Currently over 50 amphiphilic drugs are known. Unique pharmacological properties necessitate clinical use of some of these drugs. The occurrence and severity of potential clinical side effects depend on the nature of each drug, dosage and duration of treatment, simultaneous administration of other drugs and foods, individual metabolic pattern of the patient and other factors. Further studies on factors preventing and potentiating adverse effects of amphiphilic drugs are indicated.

Responses of lymphocytes to anisotonic media: volume-regulating behavior

The regulatory responses elicited in lymphoid cells suspended in anisotonic media are reviewed. The immediate response approximates osmometric behavior. In addition, in hypotonic media, the initial osmometric swelling is followed by a regulatory volume decrease (RVD), which is associated with KCl loss. The volume-induced effluxes of K+ and Cl- are mediated by two independent conductive pathways. Ca2+-depletion experiments and studies of inhibitor susceptibility suggest that Ca2+ may mediate the activation of the K+ pathway. The responses of the two main lymphocyte subpopulations to hypotonic challenge are different. RVD is much more rapid in T- than in B-cells, regardless of their tissue of origin. Under certain conditions, shrunken lymphocytes will regain their initial volume. This regulatory volume increase (RVI) is due to NaCl uptake, followed by a secondary exchange of Na+ for K+ via the Na+-K+ pump. Na+ is primarily taken up in exchange for H+ through an amiloride-sensitive pathway, whereas Cl- enters in exchange for HCO-3 (or OH-). Anion and cation fluxes responsible for RVI are electroneutral. Some of the volume-sensitive pathways can also be activated in isotonic cells. The conductive K+ pathway is activated by Ca2+ plus ionophore A23187, and the Na+-H+ exchanger can be activated by cytoplasmic acidification. The responses of lymphocytes to anisotonic challenge are compared with those of other cells, and the possible significance of the volume-induced fluxes is discussed.

Ionic currents in two strains of rat anterior pituitary tumor cells

The ionic conductance mechanisms underlying action potential behavior in GH3 and GH4/C1 rat pituitary tumor cell lines were identified and characterized using a patch electrode voltage-clamp technique. Voltage-dependent sodium, calcium, and potassium currents and calcium-activated potassium currents were present in the GH3 cells. GH4/C1 cells possess much less sodium current, less voltage-dependent potassium current, and comparable amounts of calcium current. Voltage-dependent inward sodium current activated and inactivated rapidly and was blocked by tetrodotoxin. A slower-activating voltage-dependent inward calcium current was blocked by cobalt, manganese, nickel, zinc, or cadmium. Barium was substituted for calcium as the inward current carrier. Calcium tail currents decay with two exponential components. The rate constant for the slower component is voltage dependent, while the faster rate constant is independent of voltage. An analysis of tail current envelopes under conditions of controlled ionic gradients suggests that much of the apparent decline of calcium currents arises from an opposing outward current of low cationic selectivity. Voltage-dependent outward potassium current activated rapidly and inactivated slowly. A second outward current, the calcium-activated potassium current, activated slowly and did not appear to reach steady state with 185-ms voltage pulses. This slowly activating outward current is sensitive to external cobalt and cadmium and to the internal concentration of calcium. Tetraethylammonium and 4-aminopyridine block the majority of these outward currents. Our studies reveal a variety of macroscopic ionic currents that could play a role in the initiation and short-term maintenance of hormone secretion, but suggest that sodium channels probably do not make a major contribution.

Uptake of lactoferrin by the liver. III. Critical role of the protein moiety

Three possible modes of recognition of human lactoferrin (Lf), which is avidly taken up by the mouse liver, were examined. First, Lf has terminal galactosyl residues for which a receptor exists on hepatocytes. However, when large amounts of Lf were injected with 125I-asialoorosomucoid, no inhibition of asialoorosomucoid uptake by the liver was observed. Second, Lf that exposes fucosyl residues could be recognized by the sugar-polyspecific receptor of liver sinusoidal cells. Digestion of Lf by fucosidase did not affect considerably the uptake of Lf. In addition, bovine Lf, which lacks fucosyl residues, was also avidly taken up by the liver, and this uptake was inhibited by human Lf. Mannan and horseradish peroxidase, which are recognized by the sugar-polyspecific receptor, did not inhibit Lf uptake. These data demonstrate that galactosyl and fucosyl residues are not essential for Lf recognition. Third, Lf could be recognized by its protein moiety. To investigate this possibility, we used two Lf derivatives with intact carbohydrate side chains, carbamylated Lf and the C-terminal half molecule of Lf. Carbamylation reduced the uptake of Lf and its competitive activity toward the uptake of 125I-Lf. The C-terminal fragment, like carbamylated Lf, had a much weaker competitive activity than intact Lf. Therefore, the integrity of the protein moiety of Lf was required for its effective uptake by the liver. As Lf is a cationic protein, competition experiments were also done with lysozyme, another cationic protein which in the form of dimer is taken up by the liver reticuloendothelial system. The strong inhibition by dimerized lysozyme suggests that the liver reticuloendothelial system has common binding sites for certain cationic proteins, as recently shown for isolated macrophages.

Recent advances in metal carcinogenesis

Recent advances in metal carcinogenesis are comprehensively reviewed, including (a) epidemiological and clinical aspects, (b) carcinogenesis bioassays, (c) bacterial mutagenesis, (d) mammalian cell mutagenesis, (e) chromosomal damage, (f) mammalian cell transformation, (g) microsomal metabolism, (h) DNA strandbreaks and crosslinks, (i) DNA polymerase infidelity, (j) RNA strand initiation, and (k) helical transition of B-DNA to Z-DNA. Based upon these observations, several hypotheses are proposed for the molecular pathogenesis of carcinogenesis by metal compounds. These hypotheses are amenable to experimental test by existing techniques of molecular biology.

Diffusion of ions and indicator dyes in neural cytoplasm

The dispersion of dye molecules and small cations injected from a point source in the cytoplasm of molluscan neurons has been measured photometrically and compared with dispersion in aqueous solution. The diffusion of phenol red and arsenazo III was at least a factor of five slower in the cytoplasm than in saline. Movement of both dyes was slowed by about the same factor in a given cell. The dispersion rate of arsenazo III was not significantly affected by preloading the cytoplasm to dye concentrations up to 0.5 mM. Calcium and barium dispersion was measured in neurons and saline droplets preloaded with arsenazo III, while phenol red absorbance changes were used to follow the dispersion of injected protons. Ba2+ and H+ moved very slowly in the cytoplasm compared to aqueous solution. Ca2+ movement in all probability underwent a similar retardation in the neurons but high-affinity buffering of the cytoplasm severely restricted the spread of detectable amounts of this ion away from the injection site.

[Regulation of ion transport in mitochondria by respiratory chain enzymes and ATPase]

The effects of the respiratory chain inhibitors as well as those of the inhibitors and substrates of ATP-synthetase in Ca2+ and K+ transport induced in the mitochondria upon the medium acidification in the presence of phosphate or arsenate, were investigated. Evidence has been obtained suggesting that under the experimental conditions used the transmembrane fluxes of K+ and Ca2+ are paralleled with H+ leakage through the proton channel of ATPase. It was found also that the system inducing cation fluxes at low pH values included peroxidation and hydrolysis of phospholipids. A scheme of regulation of ion transport in the mitochondria involving oxidative phosphorylation and oxidation and hydrolysis of lipids is proposed.

Cation excretion and kallikrein secretion by the rat parotid gland in various hypertensive models

The major salivary glands are distinguished by a high kallikrein content, localized particularly in regions with intense electrolyte transport (the apical border of striated duct cells and the luminal border of the main excretory ducts). For this reason we used the parotid gland as a test model for investigations on electrolyte (sodium and potassium) and kallikrein transport in various forms of experimental hypertension [spontaneously hypertensive rats, renovascular (two-kidney one-clip) hypertension, and deoxycorticosterone trimethylacetate (DOCA)-salt hypertension]. As compared with values for the controls, the sodium concentration in parotid saliva was decreased in all hypertensive models studied, indicating enhanced sodium reabsorption in the glandular duct system. In DOCA-salt hypertension the flow rate dependency of the sodium concentration was preserved. In contrast, in genetic and renovascular hypertension, the decreased sodium concentration was independent of the salivary flow rate. Salivary potassium concentration showed an inverse relationship to sodium level and was slightly increased in DOCA-salt and renovascular hypertension. In genetic hypertension potassium concentration in saliva was lowered. Salivary kallikrein activity was enhanced in all forms of hypertension studied, with the highest increase in genetic hypertension (factor 3.5), followed by DOCA-salt hypertension (factor 3.0) and finally by renovascular hypertension (factor 2.5). The pathogenesis of the exaggerated kallikrein secretion observed in hypertension is discussed with regard to a counterregulatory mechanism as well as sympathicoadrenergic activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Permeability to various cations of the voltage-dependent sodium channel of rat single heart cells

The permeability to various cations of the voltage-dependent sodium channel of rat single heart cells has been studied under the current or voltage clamp conditions. The cells, dispersed by collagenase treatment, were perfused internally using a suction pipette technique. The permeability sequence, estimated from the effects of various cations on the maximum rate of rise of action potential or from either the peak amplitude or the reversal potential of the inward current was Na+ greater than Li+ greater than hydrazine greater than guanidine greater than formamidine greater than hydroxylamine greater than methylguanidine greater than monomethylamine. The ionic permeability of a compound was markedly diminished by methylation. All inorganic and organic cation currents were reduced in the presence of tetrodotoxin, a specific Na+ channel blocker. It would appear that the ionic selectivity of the sodium channel of rat single heart cells is similar to the selectivity in the squid axon and of that in the myelinated nerve of the frog.

Ion content and the response of L5178Y-R and L5178Y-S cells to X rays and ionophore A23187

We examined the response of L5178Y-S (radiosensitive, LY-S) and L5178Y-R (radioresistant, LY-R) lymphoblasts to X-irradiation with concomittant treatment with divalent cation ionophore, A23187 (3 h or 5 h, 5 micrograms/ml). Cells treated with A23187 alone progressed through the cell cycle more slowly than the untreated cells and their cloning efficiency was reduced. In both cell strains the ionophore prolonged duration of the postirradiation mitotic delay. Radiation-induced inhibition of DNA synthesis was reversed by A23187 in LY-S but not in LY-R cells. Cells subjected to the ionophore treatment survived X-irradiation in almost the same way as untreated cells, as if the effect of A23187 treatment were reversed by irradiation. There was also a reversion in the ion content: A23187 caused a marked increase in Na+ content and a decrease in K+ content, irradiation itself did not change the ion content, whereas in the A23187-treated cells it restored almost the same pattern as that found in the control cells. We found less Mg2+ ions in LY-S cells after treatment with A23187 and A23187 + X than in LY-R cells, in relation to untreated (control) cells. These observations point to the possible importance of ion transport for recovery from radiation damage.

Voltage-clamp study of the conductance activated at fertilization in the starfish egg

Ionic currents underlying the fertilization potential of the egg of the starfish Mediaster aequalis were studied using a two-micro-electrode voltage clamp. Mature eggs were fertilized in vitro under voltage-clamp conditions. The fertilization current, here termed IF, was induced by adding sperm to sea water bathing the egg. At a holding potential of -70 mV, IF was inward. It reached a peak within 2-4 min and then decayed over the next approximately 20 min with a rate which depended on the holding membrane potential. Instantaneous current-voltage relations measured at different times during IF were approximately linear and reversed at a potential of +6.0 +/- 5.8 mV (mean +/- S.D., n = 11). Membrane chord conductance was highest at the peak of inward current and the declining phase of IF was due to a decrease in conductance towards the pre-fertilization level. When the membrane potential was rapidly stepped to levels more positive than about -45 mV, the conductance underlying IF decreased in a manner which depended on both membrane potential and time. The fertilization-specific conductance showed a sigmoidal activation curve between -50 and +10 mV with a half-activation level of -25 mV. Analysis of the steady-state voltage dependence indicated that at the peak of the fertilization potential (+10 to +15 mV) only 4-5% of the total available channels would be open. Current relaxations followed first-order kinetics and the relaxation time constant depended upon the membrane potential during the voltage pulse. The relation between the time constant and voltage was bell-shaped, decreasing at potentials more negative than -40 and more positive than 0 mV. Both the steady-state conductance-voltage relation and the kinetics of the current relaxations were consistent with a simple two-state gating model in which the probability of a channel being open is determined by a single gating particle with an effective valency of -1.7 moving through the entire membrane field. The shifts in reversal potential with changes in external Na (at 10 mM-external K) were analysed using the constant field expression, which gave a relative permeability of Na to K of approximately 0.6.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of a potassium-deficient diet on arterial blood pressure, plasma and tissue cations, and tissue norepinephrine in the hypertensive dog

Chronic potassium deficiency in one-kidney one-clip hypertensive dogs significantly reduces blood pressure and plasma potassium, with a simultaneous increase in plasma renin activity. Tissue potassium concentration was decreased and tissue sodium concentration was increased in striated muscle and adrenal glands, which may suggest that the sodium-potassium pump was inhibited. In myocardium the sodium concentration was higher but the potassium concentration was not significantly lower than in control hypertensive dogs on normal diets. Arterial cation concentrations in the potassium-deficient group were not significantly different from those in the control group. Tissue norepinephrine concentration was higher in arteries from potassium-deficient animals, significantly so in the mesenteric and femoral arteries. The conclusion is that potassium deficiency may decrease blood pressure in the one-kidney one-clip hypertensive dogs by impairing the release of norepinephrine.

Human peritoneal macrophage cytotoxicity mediated by cytophilic IgG

Cells of the human mononuclear phagocyte system have recently been shown to possess cytophilic IgG molecules that promote phagocytosis of staphylococci bearing cell-wall protein A. In the present study, the possible mediation of a cytotoxic response to 51Cr-labeled sheep erythrocytes coated with protein A by cytophilic antibodies on human peritoneal macrophages was evaluated. The target cells were readily lysed by peritoneal macrophages. Cytotoxicity was blocked by pretreatment of macrophages with soluble protein or with anti-Fc F(ab')2 fragments. In contrast, cytotoxicity was not affected by cytochalasin B; this finding suggests that cytolysis is an extracellular event. Perturbation of cytophilic IgG with particle-bound protein A elicited a chemiluminescent response from peritoneal macrophages; however, experiments with scavengers of reactive oxygen species indicated that toxic oxygen radicals may not be required for cytotoxicity. The results indicate that cytophilic antibody-mediated cytotoxicity may contribute to cellular injury as well as host-defense aspects of the inflammatory process.

Comparative study of physiochemical properties of two pike parvalbumins by means of their intrinsic tyrosyl and phenylalanyl fluorescence

Physicochemical properties of two pike parvalbumins (pI 5.0 and 4.2), belonging to two different gene lineages, have been studied by their intrinsic tyrosine and phenylalanine fluorescence. The CD sites of these paravalbumins have similar affinities to Ca2+ (and Mg2+) ions, but the EF sites of the proteins have very different affinities to these ions. This results in differing stabilities of these parvalbumins to pH-, urea-, and temperature-induced denaturation. The structure of pike parvalbumin pI 5.0, which binds Ca2+, and Mg2+ ions more tightly, is more stable than that of parvalbumin pI 4.2. Both proteins have higher affinities for Na+ ions than for K+ ions.

Direct spectrophotometric detection of cation flux in membrane vesicles: stopped-flow measurements of acetylcholine-receptor-mediated ion flux

The development of a spectrophotometric stopped-flow method to measure ion flux in membrane vesicles in the millisecond to minute time region is described in detail. The technique is based on fluorescence quenching of an entrapped fluorophore (anthracene-1,5-disulfonic acid) by Cs+. The method has been applied to the measurement of acetylcholine-receptor-mediated ion flux in membrane vesicles prepared from the electric organs of both Electrophorus electricus and Torpedo californica. The method is applicable to any vesicle system in which Cs+ can substitute for either Na+ or K+. Loading of vesicles with the fluorescent dye is accomplished using the routine procedure for making the vesicles. The dye-loaded vesicles can be stored in liquid nitrogen before use. Neither the dye-loading procedure nor the presence of Cs+ changes the permeability of the membrane to ions, allowing ion-translocation measurements to be made in the millisecond to minute time region. The stopped-flow design presented allows two sequential mixings of solutions. The relationship between fluorescence quenching and ion flux as well as the interpretation of the ion flux data is described. It is shown that the data obtained with stopped-flow and Cs+ is identical to data obtained previously using a quench-flow technique and 86Rb+. The advantages of the present method over the quench-flow technique and a similar stopped-flow technique developed previously based on T1+ are described in detail.

Mechanism of epithelial lithium transport. Evidence for basolateral Na:Na and Na:Li exchange

Measurement of transmural sodium fluxes across isolated, ouabain-inhibited turtle colon in the presence of a serosal-to-mucosal sodium gradient shows that in the absence of active transport the amiloride-sensitive cellular path contains at least two routes for the transmural movement of sodium and lithium, one a conductive path and the other a nonconductive, cation-exchange mechanism. The latter transport element can exchange lithium for sodium, and the countertransport of these two cations provides a mechanistic basis for the ability of tight epithelia to actively absorb lithium despite the low affinity of the basolateral Na/K-ATPase for this cation.

Ionic movements through light-sensitive channels of toad rods

Electrical photoresponses of rods in the isolated toad retina were recorded during ionic manipulations of the Na+-free extracellular medium. In the presence of a concentration of external Ca2+ above 10(-5) M, voltage photoresponses were observed only in the presence of external Na+ or Li+. When external Ca2+ was reduced below 10(-6) M, voltage photoresponses of normal polarity could be detected even in the absence of Na+ or Li+, but in the presence of external Mg2+. In the presence of normal extracellular Ca2+ hyperpolarizing photoresponses were observed even in the absence of Na+ or Li+, provided small amounts of phosphodiesterase inhibitors (IBMX, RO 20-1724, papaverine, caffeine, theophylline) were added to the perfusate. Responses obtained in low-Na+ IBMX solutions required the presence of millimolar amounts of a variety of divalent cations, among which Mn2+ and Ba2+ were the most effective. When the concentration of both external Ca2+ and Mg2+ was reduced to micromolar amounts, depolarizing photoresponses were observed. In these conditions measurements with radioactive tracers showed a light-modulated efflux of 42K+ or 86Rb+. The light-modulated 42K+ or 86Rb+ efflux was halved by 2 X 6 mM-external K+ and was completely blocked when K+ was raised above 10 mM. These results show that ionic movements through light-sensitive channels are controlled by Ca2+ and Mg2+ and possibly also be the intracellular level of cyclic nucleotides. Moreover, the movement of ions through the light-sensitive channel, does not obey the independence principle.

Effect of experimental acute renal failure on intrinsic renal tubular secretory clearance of organic cations in rats

Effect of experimental acute renal failure (EARF) on the intrinsic renal tubular secretory clearance (CLscnint) of tetraethylammonium bromide (TEA) and N1-methylnicotinamide (NMN) was examined in rats treated with glycerol, folate, salicylate, uranium and gentamicin. The values of CLscnint was calculated by an equation incorporating the determinants of the renal clearance (CLr), i.e., renal tubular secretory clearance (CLscnr), glomerular filtration rate (GFR), renal plasma flow (RPF), free fraction of the drug in plasma (fp) and fraction (Freabs) of the drug reabsorbed after filtration and secretion in the urine. In the EARF-rats, the values of CLscnint of NMN and TEA were decreased by 0.017-0.575 times and by 0.005-0.737 times as compared to those of the normal rats, respectively. It was suggested that the decreases in CLscnr of both NMN and TEA were due not to the decrease in RPF, but to that in CLscnint.