Renal tubule transport of organic cations

Transcellular active tubular transport of organic cations occurs in the proximal renal tubule in the direction of excretion. These organic cations may be primary, secondary, tertiary, or quaternary amines. Endogenous neurohumors such as choline and catecholamines and drugs such as morphine and tetraethylammonium are representative transportable organic cations. Competitive inhibition for transport is found among organic cations. Organic anions, however, do not compete for this transport. Organic cations used as drugs may interact with the transport of endogenous organic cations to alter the excretion patterns of both. Bidirectional active tubule transport can be demonstrated for choline and is accompanied by simultaneous renal metabolism of choline. Studies using vesicles prepared from luminal and antiluminal membranes of renal cortex suggest that organic cation transport occurs in both vesicle preparations. However, only the luminal vesicles showed the characteristics of carrier-mediated uphill transport.

Amiloride-resistant Madin-Darby canine kidney (MDCK) cells exhibit decreased cation transport

Cation transport systems were investigated in mutant Madin-Darby Canine Kidney (MDCK) cells resistant to the diuretic drug amiloride. The mutants were isolated previously as clones resistant to the cytotoxic effects of 3 X 10(-4) M amiloride. Decreased amiloride transport by the Na+ channel was implicated as the basis of the resistance (Taub, '78). Consistent with this hypothesis, Na+ accumulation was lower in amiloride-resistant cells than in normal sensitive MDCK cells. Kinetic studies indicated that Na+ uptake in MDCK cells occurs by a single ATP independent transport system--the Na+ channel. In several amiloride-resistant clones, including clone Amr2, the decreased Na+ uptake was associated with a decrease in both the Km and Vmax for Na+ uptake by the Na+ channel. In Amr2 cells no significant alteration in the inhibitory effect of amiloride on Na+ uptake was observed. As the Na+ channel may actually be a general uptake system for monovalent cations (a number of cations inhibit Na+ uptake), the uptake of these inhibitory cations was examined in Amr2 cells. Both Ca++ and ouabain-insensitive Rb+ uptake occurred at decreased rates in Amr2 cells as compared with normal MDCK cells. However, further uptake studies suggested that Na+, Ca++ and ouabain-insensitive Rb+ uptake all occur by different systems. Thus several transport systems may be defective in Amr2 cells. Amr2 cells were also resistant to the inhibitory effects of amiloride on CO2 evolution from pyruvate. These observations indicate that alterations at a number of molecular sites may be associated with defective Na+ transport via the Na+ channel in amiloride-resistant cells. Thus the amiloride-resistant cells are potentially valuable in examining the interrelationships between Na+ transport and other cellular functions.

Effect of arachidonic acid and the chemotactic factor F-Met-Leu-Phe on cation transport in rabbit neutrophils

A detailed examination of the effects of exogenous arachidonate on cation metabolism in rabbit neutrophils was undertaken. Arachidonic acid stimulates the movement of 45Ca into and out of the neutrophils with a net result, in the presence of extracellular calcium, of increasing the steady-state level of 45Ca. Arachidonate also increases the uptake of 22Na. These effects of arachidonate are specific to these cations, concentration-dependent, and sensitive to lipoxygenase inhibitors. At the concentrations used in this study arachidonate does not influence the permeability of human erythrocytes to 45Ca. Furthermore, both arachidonic acid and F-Met-Leu-Phe release calcium from a previously unexchangeable intracellular pool and the effect of the two stimuli are not additive. Arachidonic acid-dependent, but not F-Met-Leu-Phe-dependent, calcium release is sensitive to lipoxygenase inhibitors. These two stimuli thus appear to release calcium from the same pool(s) by separate mechanisms. The results summarized above are consistent with the hypothesis that one or more arachidonate metabolites are involved in the mechanism underlying the chemotactic factor induced permeability changes in rabbit neutrophils.

Effects of 5 alpha-dihydrotestosterone and methandrostenolone in male guinea pigs

Young adult guinea pigs were studied 6 and 9 weeks after silastic capsules containing 5 alpha-hydrotestosterone (5 alpha-DHT) and methandrostenolone (Dianabol) were implanted. DHT was more effective in causing testicular atrophy and was apparently more androgenically potent in sustaining the size of the seminal vesicles. Both steroids led to hypertrophy of the masseter muscle and increase in gastrocnemius protein concentration. Cardiac tissue was sensitive to the effects of these steroids, particularly to the larger amounts of absorbed Dianabol, in terms of increases in DNA concentration and transient loss of tissue sodium, potassium, and calcium. All alterations in muscle composition occurred in the total absence of change in tissue water. Hypernatremia and hyperkalemia was present in steroid-treated animals with significant loss of urinary potassium in DHT-treated guinea pigs. Adrenal atrophy and the lowering of circulating cortisol was further indicative of effects upon adrenocortical function and the regulation of electrolyte balance.

Role of cations in the regulation of baker's yeast AMP deaminase

The effect of polyamines and divalent cations including alkaline earth metals and transition metals on the AMP deaminase (AMP aminohydrolase EC 3.5.4.6) purified from baker's yeast was investigated. (1) Polyamines and alkaline earth metals activated the enzyme in the absence of ATP: these cations largely enhanced the maximal velocity without alteration of S0.5 and nH (Hill coefficient) values. However, transition metals acted as potent inhibitors, which decreased the maximal velocity of the enzyme in the absence of ATP. (2) All of the divalent cations showed an activation of the enzyme in the presence of ATP, followed by a progressive decrease in activity as the concentrations of transition metals increased. (3) The increase in the concentrations of polyamines or alkaline earth metals showed no more activating effect when the enzyme was fully activated by the addition of excess alkali metals in the absence of ATP, but divalent cation-activation was observed in the presence of ATP even if alkali metals were saturating. These results suggest the presence of two types of binding sites for cations: 1, the sites for free cations and 2, those for ATP-metal complexes. The former sites include the activating sites for alkali metals, polyamines and free alkaline earth metals, and the inhibitory sites for free transition metals. The latter sites are the activating sites for ATP-metal complexes, which are suggested to be commonly occupied by alkaline earth metals and transition metals and to form an ATP bridge (E-ATP-M) complex.

Ultrahistochemical and autoradiographic evidence of epithelial transport in the uterus of the ovoviviparous salamander, Salamandra salamandra (L.) (Amphibia, Urodela)

The uterine epithelium of pregnant females of the terrestrial ovoviviparous Salamandra salamandra is characterized by a considerable enlargement of its basolateral surface. Chloride and cations (among others sodium), preferentially within the intercellular spaces, can be demonstrated ultrahistochemically. There is indirect evidence of Na+ --K+ -ATPase activity along the basolateral plasma membranes of the epithelial cells using the Sr-technique for demonstration of a K+ -NPPase and 3H-ouabain autoradiography. Preliminary measurements reveal a potential difference across the uterine wall of 15--25 mV, the lumenal (mucosal) surface being negative with respect to the coelomic (serosal) surface, and a short circuit current of 200--300 microA. The possible electrogenic ion transport is ouabain-sensitive. The results are in agreement with the model of a "forward" transporting, i.e. absorptive epithelium. An active transport of solute out of the uterine lumen across the epithelium to the subjacent connective tissue and the blood vessels may be involved in the regulation of an intrauterine milieu appropriate for the development of the offspring.

Modification of adrenochrome-induced cardiac contractile failure and cell damage by changes in cation concentrations

Adrenochrome has been shown to produce cardiac necrosis as well as failure in the isolated rat hearts. These effects of adrenochrome were influenced by alterations in the Ca2+, Na+, K+, and Mg2+ concentrations of the perfusion medium. Increasing the Ca2+ or K+ concentration or decreasing the Na+ concentration of the adrenochrome-containing perfusion medium partially maintained contractile force but increased the severity of ultrastructural damage. Reducing the K+ concentration of the medium did not alter the failure of contractile force development but increased the severity of ultrastructural damage due to adrenochrome. Reducing the Ca2+ or increasing the Mg2+ concentration of the perfusion medium completely prevented myocardial necrosis due to adrenochrome. Omission of Mg2+ from the perfusion medium neither altered the time course of contractile failure nor effected the severity of necrosis due to adrenochrome. These results for the most part parallel the influence of similar ionic interventions on the severity of necrosis produced by excessive amount of catecholamines.

Mechanisms of organic cation transport in kidney plasma membrane vesicles: 1. Countertransport studies

Transport for organic cations has been described in both luminal and antiluminal membranes. The two transport systems difer from one another on the basis of kinetic parameters and countertransport. By using N1-[3H]methylnicotinamide as the indication cation, a series of organic cations (which were known to be secreted) were tested for their capacity to stimulate countertransport. The phenomenon of countertransport was symmetrical in that it was observed for both influx and efflux in both membranes. However, under appropriate conditions, certain organic cations were effective in producing "uphill" transport of N1-[3H]methylnicotinamide in the luminal membrane and the effect was limited to that membrane exclusively. Detailed analysis of countertransport in the luminal membrane showed quantitative differences in the maximal stimulation produced by the various cations: giving rise to the relationship that the concentration of organic cation which gave one-half maximal N1-[3H]methylnicotinamide countertransport approximated its affinity constant. The data were interpreted to suggest that all the members of the organic cation series tested are translocated across the luminal membrane by the same carrier but that they are moved at different rates.

Negative hydrophobic ions as transport-mediators for positive ions: evidence for a carrier mechanism

The permeability of hydrophobic cations, such as tetraphenylarsonium across biological membranes and artificial lipid membranes is strongly increased in the presence of trace amounts of hydrophobic anions like tetraphenylborate (Liberman, Y.A. and Topaly, V.P. (1969) Biofizika 14, 452--461). Voltage-jump relaxation experiments performed on thin lipid membranes support the idea that the anions, A-, act as carriers for the cations, B+, by the formation of neutral ion pairs, A-B+. Their permeability is not affected by the electric dipole potential, which hinders the movement of free cations, B+.

Chemical basis for selectivity of metal ions by the Bacillus subtilis cell wall

The use of equilibrium dialysis techniques established that isolated cell walls of Bacillus subtilis possess selective affinities for several cations. The binding of these cations to the cell wall was influenced by the presence of various functional groups in the peptidoglycan matrix. Selective chemical modification of the free carboxyl and amino groups showed that when amino groups were replaced by neutral, bulky, or negatively charged groups, the sites available for cation complexing generally increased. Introduction of positive charges into the wall resulted in a marked decrease in the numbers of metal binding sites and usually a decrease in the apparent association constants. Both teichoic acid and peptidoglycan contribute to the sites available for interaction with metals. Hill plots of equilibrium dialysis data suggest that metal binding to cell walls involves negative cooperativity. Competition between various metals for binding sites suggested that the cations complex with identical sites on the cell walls. When the hydrogen ion concentration was increased, the affinity of the walls for metals decreased, but the numbers of metal binding sites remained constant, suggesting that cations and protons also compete for the same sites.

Liver pyridoxal kinase-interaction with metal ions

The binding of some mono- and divalent cations to liver pyridoxal kinase induces spectral changes. These changes in the UV absorption spectrum are consistent with our reported specificities of essential activation with K+ and NH+4 ions and low concentration of Zn2+ and much higher concentration of Mn2+.

Characteristics of 5-hydroxytryptamine transport in pancreatic islets

1 Transmembrane transport of 3H-labelled 5-hydroxytryptamine (5-HT) by isolated pancreatic islets of non-inbred ob/ob mice was studied. 2 5-HT was vigorously accumulated in a temperature-dependent way by the islet cells. 3 Studies of the concentration-dependence of [3H]-5-HT uptake revealed complex kinetics with one component being saturated at 1 to 3 microM 5-HT (apparent association constant 0.6 x 10(6) M(-1) and the other non-saturated up to 1 mM 5-HT. 4 The saturable uptake was inhibited by Na+-deficiency and metabolic poisoning with 2,4-dinitrophenol and antimycin A, whereas the non-saturable component was not affected. 5 Omission of K+, Ca2+ or Mg2+ did not affect the uptake rate. 6 It is concluded that 5-HT is taken up by pancreatic beta-cells by mechanisms very similar to those observed in thrombocytes and neurones.

Insulin receptors in rabbit erythrocyte

The existence of insulin receptors in rabbit erythrocytes was studied by evaluating the specific binding of 125I-insulin to erythrocyte membranes. The binding of 125I-insulin was pH, time and temperature dependent. Maximal binding was achieved by incubation for 20 hr at 0 degrees C. The optimum pH was 7.4. Treatment with cations and enzymes enhanced the specific binding except for with trypsin, the treatment which greatly reduced the binding. Unlabeled insulin over a wide range of concentrations competitively inhibited the binding of 125I-insulin, while the binding was little affected by structurally unrelated hormones. Scatchard plot was represented as a concave curve. Binding sites of relatively high affinity (K1 = 0.9 X 10(9) M-1) and low capacity (8.0 X 10(13)/g protein) could be distinguished from those of lower affinity (K2 = 0.8 X 10(7) M-1) and higher capacity (1.8 X 10(15)/g protein). Hill's analysis and dissociation of 125I-insulin from membranes demonstrated the characteristics of negative cooperation between receptor sites. Both incorporation of H3(32)PO4 to erythrocyte membranes and uptake of 45Ca were significantly reduced by the addition of unlabeled insulin. Unlabeled insulin produced no effect on uptake of 45Ca into trypsin-treated erythrocytes. On the basis of these results, it was suggested that rabbit erythrocytes might possess biologically significant insulin receptors located on the cell membranes.

Accumulation of drugs by resting or beating cardiac tissue

The rate and degree of accumulation of 12 neutral, anionic and cationic drugs were studied in resting and 2 Hz-stimulated isolated left auricles of the guinea pig. The uptake process was accelerated in muscles driven electrically. The time needed to reach equilibrium was related to the extent of accumulation which in turn corresponded with the lipophilicity of the drug. The frequency-induced changes in the kinetics of the accumulation disappeared under reduced mechanical activity of the muscle. It is suggested that the increased mechanical activity enhances drug disposition within the extracellular space, so that more drug is available for transmembrane penetration.

Quantitating ruminal turnover

Basic principles of in vivo kinetics are reviewed as they apply to the digestive process in ruminants. Emphasis is on application and limitations of techniques for measuring ruminal turnover of undigested feed residues. This turnover can best be measured by using feed particles whose organic constituent(s) contain uniform concentrations of an isotope. Alternatively, rare earths remain attached to feed residues throughout the digestive tract and can also be used. Appropriate application of mathematical methods must consider ingestaflow as a multicompartment process.

Inhibition of anion permeability of sarcoplasmic reticulum vesicles by 4-acetoamido-4'-isothiocyanostilbene-2,2'-disulfonate

The permeabilities of sarcoplasmic reticulum vesicle membrane for various ions and neutral molecules were measured by following the change in light scattering intensity due to the osmotic volume change of the vesicles. 4-Acetoamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS), which is a potent inhibitor for the anion permeability of red blood cells membrane, inhibited the permeability of sarcoplasmic reticulum for anions such as Cl-, Pi and methanesulfonate, while it slightly increased that for cations and neutral molecules such as Na+, K+, choline and glycerol. Binding of 5 mumol SITS/g protein was necessary for the inhibition of anion permeability. These results suggest the existence of a similar anion transport system in sarcoplasmic reticulum membrane as revealed in red blood cell membrane.

Comparison of ionic selectivity of batrachotoxin-activated channels with different tetrodotoxin dissociation constants

The purpose of these experiments is to test whether the differences between normal and tetrodotoxin-resistant Na+ channels reside in the selectivity filter. To do this, we have compared the selectivity of batrachotoxin-activated channels for alkali cations, organic cations, and nonelectrolytes in two neuroblastoma clonal cell lines: N18, which has normal tetrodotoxin (TTX) sensitivity, and C9, which is relatively TTX-resistant. We have also studied the effect of H+ on Na+ permeability and on the interaction between TTX and its receptor site in both cell lines. There is no qualitative difference between the two cell lines in any of these properties. In both cell lines the batrachotoxin-activated Na+ channels have a selectivity sequence of Tl+ greater than Na+ greater than K+, guanidinium greater than Rb+ greater than Cs+, methylamine. Also, in both cell lines H+ blocks Na+ channels with a pKa of 5.5 and inhibits the action of TTX with the same pKa. These observations indicate that the selectivity filters of the Na+ channels in C9 and N18 do not differ significantly despite the 100-fold difference in TTX-affinity. Our selectivity studies of batrachotoxin-activated Na+ channels for both cell lines suggest that these toxin-activated Na+ channels have a limiting pore size of 3.8 x 6.0 A, as compared to a pore size of 3.0 x 5.0 A for potential-activated Na+ channels.

The effect of spironolactone on the arterial water, cation, and norepinephrine contents of control and 'one-kidney-one-clip' hypertensive dogs

Spironolactone at 10 mg per kilogram per day was given to control and 'one-kidney-one-clip' hypertensive dogs for 6--7 weeks. Compared with untreated animals the treated animals had a lower arterial water content, a higher arterial, myocardial, and skeletal muscle sodium content, and variable changes in tissue potassium concentrations.

Effect of primycin on monovalent cation transport of erythrocyte membrane and lipid bilayer

The effects of primycin were investigated on the alkali-cation transport of human erythrocytes and on the electric conduction of bimolecular lipid membranes. In the concentration range of 3.10(-6) approximately 10(-5) M primycin increased the permeability of erythrocytes to alkali-cations according to the sequences Cs+ greater than Rb+ approximately K+ greater than Na+, while the conductance of the negatively charged phosphatidylserine bimolecular lipid membrane increased by 2 approximately 3 orders of magnitude. The resistance-lowering effect of primycin strongly depended on the cationic species applied and a selectivity order Na+ greater than K+ greater than Rb+ greater than Cs+ was found. A possible mechanism of the primycin-membrane interaction is suggested on the basis of experimental data.

The Feldberg Lecture 1976. Solute transport across epithelia: what can we learn from micropuncture studies in kidney tubules?

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Determinants of the renal handling of 2, 4-dichlorophenoxyacetic acid by winter flounder

The factors determining the renal handling of 2,4-dichlorophenoxyacetic acid (2,4-D) were examined in winter flounder, Pseudopleuronectes americanus, using isolated tubules and clearance techniques. In vitro, extensive energy-dependent uptake was seen with tissue/medium ratios of 30-fold at 1 micronM 2,4-D. The velocity of uptake was concentration-dependent with apparent Km and Vmax v,lues of 70 micronM and 3.6 micronmol/g of tubules per hr, respectively. Uptake was inhibited by other organic acids and 2,4-D competitively inhibited p-aminohippurate uptake. 2,4-D did not inhibit organic cation transport by the tubules. In vivo, 2,4-D was actively secreted with clearances of nearly 500 times the glomerular filtration rate at 1 micronM 2,4-D in plasma. At higher plasma concentrations (10-60 micronM) a transport maximum of 0.85 micronmol/g of kidney per hr was observed. Secretion was inhibited by other organic acids. 2,4-D also inhibited p-aminohippurate secretion in vivo. Little metabolism was noted; approximately 10% was excreted as the taurine conjugate. Plasma binding was 70%. Examination of the effects of added proteins on in vitro uptake showed that protein binding could limit 2,4-D transport but that flounder plasma (low in albumin) was far less effective than bovine serum albumin in binding and inhibition of transport. The roles of plasma binding, intracellular binding and metabolism in determining the rate of 2,4-D elimination by the kidney are discussed.

In vivo reversibility of the jejunal glucose and cation transport alteration caused by intraluminal surfactants in the rat

Tied jejunal loops in anaesthetized rats were under standardized conditions pre-exposed for 30 min. with Tyrode solution containing surfactants. 5, 20 or 150 min. after wash out of bulk surfactant, the loops were re-instilled with Tyrode containing glucose at 5--15 mmol/l. Net glucose, sodium and potassium transport were studied for 15 min. by changes in intraluminal amounts, and compared with results obtained in control rats. The surfactants (mmol/l) tested were the anionics dioctylsulphosuccinate (5.6) and dodecylsulphate (8.5--17), the cationics cetrimonium bromide (2.1--4.1) and benzalkonium chloride (2.1), the nonionics Triton X100 (0.25%) and Lubrol WX (0.25--0.5%) plus cholic acid (4.9) and desoxycholic acid (1.3--2.5). In most cases, the glucose transport was normal or fairly normal after 150 min., most of the restoration taking place shortly after surfactant removal. However, Lubrol in particular caused more irreversible effects. Generally, the changes in net cation transport tended to be less easily reversible than the alteration in glucose transport. In so far as a normal or near to normal glucose transport is unlikely to occur unless both functional and structural integrity of the epithelium is preserved, the results indicate that in most cases there is but insignificant epithelial damage under the experimental conditions. Since, furthermore, these surfactants can interact with glucose transport in the same technique even at lower concentration and shorter incubation time than used here, it is concluded that the interaction of surfactants with intestinal transport is not neccessarily linked to gross histo-pathological changes.