Water structure as a determinant of ion distribution in living tissue

Decoupling the Na+–K+–ATPase in vivo: A possible new role in the gills of freshwater fishes

The literature suggests that when Na(+)-K(+)-ATPase has reduced access to its glycosphingolipid cofactor sulfogalactosyl ceramide (SGC), it is converted to a Na(+) uniporter. We recently showed that such segregation can occur within a single membrane when Na(+)-K(+)-ATPase is excluded from membrane microdomains or 'lipid rafts' enriched in SGC (D. Lingwood, G. Harauz, J.S. Ballantyne, J. Biol. Chem. 280, 36545-36550). Specifically we demonstrated that Na(+)-K(+)-ATPase localizes to SGC-enriched rafts in the gill basolateral membrane (BLM) of rainbow trout exposed to seawater (SW) but not freshwater (FW). We therefore proposed that since the freshwater gill Na(+)-K(+)-ATPase was separated from BLM SGC it should also transport Na(+) only, suggesting a new role for the pump in this epithelium. In this paper we discuss the biochemical evidence for SGC-based modulation of transport stoichiometry and highlight how a unique asparagine-lysine substitution in the FW pump isoform and FW gill transport energetics gear the Na(+)-K(+)-ATPase to perform Na(+) uniport.

The Cytomatrix as a Cooperative System of Macromolecular and Water Networks

Water was called by Szent-Gyorgi "life's mater and matrix, mother and medium." This chapter considers both aspects of his statement. Many astrobiologists argue that some, if not all, of Earth's water arrived during cometary bombardments. Amorphous water ices of comets possibly facilitated organization of complex organic molecules, kick-starting prebiotic evolution. In Gaian theory, Earth retains its water as a consequence of biological activity. The cell cytomatrix is a proteinaceous matrix/lattice incorporating the cytoskeleton, a pervasive, holistic superstructural network that integrates metabolic pathways. Enzymes of metabolic pathways are ordered in supramolecular clusters (metabolons) associated with cytoskeleton and/or membranes. Metabolic intermediates are microchanneled through metabolons without entering a bulk aqueous phase. Rather than being free in solution, even major signaling ions are probably clustered in association with the cytomatrix. Chloroplasts and mitochondria, like bacteria and archaea, also contain a cytoskeletal lattice, metabolons, and channel metabolites. Eukaryotic metabolism is mathematically a scale-free or small-world network. Enzyme clusters of bacterial origin are incorporated at a pathway level that is architecturally archaean. The eucaryotic cell may be a product of serial endosymbiosis, a chimera. Cell cytoplasm is approximately 80% water. Water is indisputably a conserved structural element of proteins, essential to their folding, specificity, ligand binding, and to enzyme catalysis. The vast literature of organized cell water has long argued that the cytomatrix and cell water are an entire system, a continuum, or gestalt. Alternatives are offered to mainstream explanations of cell electric potentials, ion channel, enzyme, and motor protein function, in terms of high-order cooperative systems of ions, water, and macromolecules. This chapter describes some prominent concepts of organized cell water, including vicinal water network theory, the association-induction hypothesis, wave-cluster theory, phase-gel transition theories, and theories of low- and high-density water polymorphs.

The role of water structure in conformational changes of nucleic acids in ambient and high-pressure conditions

This review describes and summarizes data on the structure and properties of water under normal conditions, at high salt concentration and under high pressure. We correlate the observed conformational changes in nucleic acids with changes in water structure and activity, and suggest a mechanism of conformational transitions of nucleic acids which accounts for changes in the water structure. From the biophysical, biochemical and crystallographic data we conclude that the Z-DNA form can be induced only at low water activity produced by high salt concentrations or high pressure, and accompanied by the stabilizing conjugative effect of the cytidine O4' electrons of the CG base pairs.

Structure and reactivity of water at biomaterial surfaces

Molecular self association in liquids is a physical process that can dominate cohesion (interfacial tension) and miscibility. In water, self association is a powerful organizational force leading to a three-dimensional hydrogen-bonded network (water structure). Localized perturbations in the chemical potential of water as by, for example, contact with a solid surface, induces compensating changes in water structure that can be sensed tens of nanometers from the point of origin using the surface force apparatus (SFA) and ancillary techniques. These instruments reveal attractive or repulsive forces between opposing surfaces immersed in water, over and above that anticipated by continuum theory (DLVO), that are attributed to a variable density (partial molar volume) of a more-or-less ordered water structure, depending on the water wettability (surface energy) of the water-contacting surfaces. Water structure at surfaces is thus found to be a manifestation of hydrophobicity and, while mechanistic/theoretical interpretation of experimental results remain the subject of some debate in the literature, convergence of experimental observations permit, for the first time, quantitative definition of the relative terms 'hydrophobic' and 'hydrophilic'. In particular, long-range attractive forces are detected only between surfaces exhibiting a water contact angle theta > 65 degrees (herein defined as hydrophobic surfaces with pure water adhesion tension tau O = gamma O cos theta < 30 dyn/cm where gamma O is water interfacial tension = 72.8 dyn/cm). Repulsive forces are detected between surfaces exhibiting theta < 65 degrees (hydrophilic surfaces, tau O > 30 dyn/cm). These findings suggest at least two distinct kinds of water structure and reactivity: a relatively less-dense water region against hydrophobic surfaces with an open hydrogen-bonded network and a relatively more-dense water region against hydrophilic surfaces with a collapsed hydrogen-bonded network. Importantly, membrane and SFA studies reveal a discrimination between biologically-important ions that preferentially solubilizes divalent ions in more-dense water regions relative to less-dense water regions in which monovalent ions are enriched. Thus, the compelling conclusion to be drawn from the collective scientific evidence gleaned from over a century of experimental and theoretical investigation is that solvent properties of water within the interphase separating a solid surface from bulk water solution vary with contacting surface chemistry. This interphase can extend tens of nanometers from a water-contacting surface due to a propagation of differences in self association between vicinal water and bulk-phase water. Physicochemical properties of interfacial water profoundly influence the biological response to materials in a surprisingly straightforward manner when key measures of biological activity sensitive to interfacial phenomena are scaled against water adhesion tension tau O of contacting surfaces. As examples, hydrophobic surfaces (tau O < 30 dyn/cm) support adsorption of various surfactants and proteins from water because expulsion of solute from solution into the interphase between bulk solid and solution phases is energetically favorable. Adsorption to hydrophobic surfaces is driven by the reduction of interfacial energetics concomitant with replacement of water molecules at the surface by adsorbed solute (surface dehydration). Hydrophilic surfaces (tau O > 30 dyn/cm) do not support adsorption because this mechanism is energetically unfavorable. Protein-adsorbing hydrophobic surfaces are inefficient contact activators of the blood coagulation cascade whereas protein-repellent hydrophilic surfaces are efficient activators of blood coagulation. Mammalian cell attachment is a process distinct from protein adsorption that occurs efficiently to hydrophilic surfaces but inefficiently to hydrophobic surfaces. (ABSTRACT TRUNCATED)

Effects of stimulation frequency on potassium activity and cell volume in cardiac tissue

We examined the effects of increases in stimulation frequency on the intracellular potassium activity and cell volume of feline and canine Purkinje fibers and feline ventricular fibers. Intracellular potassium activity was measured with potassium liquid ion exchanger microelectrodes in single- and double-barrel configuration. Cell volume was measured with an electrophysiologic technique. From single-barrel electrode recordings, intracellular potassium activities (means +/- SE) in feline Purkinje fiber, feline papillary muscle, and canine Purkinje fiber are 117.1 +/- 5.4, 87.3 +/- 3.1, and 112.4 +/- 4.4 mM, respectively, with [K]o (external potassium concentration) of 5.4 mM. Thus direct evidence for a 30-mM gradient in intracellular potassium activity from Purkinje fiber to ventricular muscle is presented. Intracellular potassium activity did not change in any tissue studied during or after 3 min of 4 Hz stimulation. The lack of change is partially explained by a reversible 2% decrease in cell volume induced by the stimulation protocol. Net losses greater than 2% seen in earlier studies probably reflect either differences between perfused vs. superfused preparations or functional sequestration of cellular potassium involved in transfers during frequency changes.

A study of binding-solubilization of some glycolytic enzymes in striated muscle in situ

The solubilization of lactate dehydrogenase (LDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and alpha-glycerophosphate dehydrogenase (GAPDH) was studied in pressed muscle as a function of ionic strength and NADH concentration. The results indicate that these factors affect the binding-solubilization of LDH and GAPDH in a similar way to their effect in dilute homogenized tissue. Alpha-glycerophosphate dehydrogenase was included as a typical soluble enzyme, since we have been unable to demonstrate its binding to subcellular fractions under any conditions. As with homogenized tissue, LDH was less susceptible to solubilization by ionic strength than GAPDH. It was demonstrated that LDH isozymes richer in heart-type subunits were more easily removed from muscle by centrifugation-imbibition than isozymes richer in the muscle-type subunits. This was interpreted as indicating that binding of the enzyme to subcellular structures was a major factor in the restricted removal of these enzymes from muscle, since only the muscle-type subunit is capable of binding to subcellular particles. It was further demonstrated that LDH could be taken up into muscle tissue, depleted in the enzyme, against an apparent concentration gradient. This was also interpreted as binding of the enzyme to the particulate structure of the muscle. Furthermore, this uptake of LDH occurred under conditions of ionic strength (0.25) and pH (7.5) that would prevent binding of the enzyme to the particulate fraction of a dilute suspension of homogenized muscle tissue. Thus, physiological conditions of pH and ionic strength do not necessarily induce solubilization of chicken breast muscle LDH in situ. Data obtained with dilute tissue homogenates, therefore, may not necessarily be easily and safely extrapolated to conditions in situ.

[Influence of environmental salinity on the diffusion fluxes of water in the Isopod Sphaeroma serratum (Frabricius)]

1.--In Sphaeroma serratum, the diffusion fluxes of water are 3 or 4 times more important in sea water (SW) than in diluted (50%) sea water. In 100% and in 50% SW influx equals the outflux. 2.--When the animal is quickly transferred from 100% SW to 50% SW, and from 50% SW to 100% SW, the outflux is instantaneously and entirely reset. 3.--The main factor of the instantaneous resettlement of the outflux seems to be the variation of the concentration of Na+ or Cl- or both together in the external medium; the Ca2+ and Mg2+ concentrations do not seem to have any effect on the diffusion flux. 4.--The validity of our results is discussed (theory of unstirred layers, blood-circulation, oxygen interchange, ultrastructure). Our results are compared with those obtained in other Crustaceans and in Fishes.

Cation diffusion selectivity in a pore model. The phosphatidylcholine/water lamellar phase

The diffusion coefficients D (cm2/s), of four monovalent cations K+, Na+, Rb+ and Cs+ and of Ca2+ have been measured in phosphatidylcholine/water lamellar phase as a function of phase hydration and temperature and in the presence of divalent cations. Diffusion rates vary strongly with phase hydration, between 10(-7) and 10(-6) cm2/s for monovalent and 10(-8) and 10(-7) for Ca2+. The activation energies obtained are relatively small (5--10 kcal/mol). As the phase water content increases, a series of diffusion sequences is obtained, corresponding to the sequences predicted by Eisenman's theory of alkali ion equilibrium selectivity. This diffusional selectivity, which depends exclusively upon non-equilibrium parameters (mobility) within the hydrophilic path is discussed in respect to current theories of pore selectivity.

A simple universal mechanism of use and conservation of energy: its application to movements of ions and other materials across cell, mitochondrial and other membranes and to oxidative phosphorylation

A single simple mechanism by which all cells might both use energy to drive active transport to all solutes and also conserve energy in the form of adenosinetriphosphate (ATP) is descirbed. The basic assumption is that injection of energy results in a conformational change of the membrane which both generates transient highly-ordered water structures on its inside surface and changes membrane permeability. Ordered water is propagated through the cell by means of cooperative interactions with proteins, so that during the ordered period intracellular water is incompatible with small cations which require strong primary hydration, but has enhanced affinity for water-structure-breaking solutes. In animal cells cytoplasmic water is ordered by the activity of the plasma-membrane-bound transport ATPases. In mitochondria and bacteria the state of ordered water is identified with the energised state, which can be generated either by passage of electrons down the electron chain, or by ATPase activity. The mechanism is shown to be consistent with the observed transport activities of mitochondria and bacteria, and also provides a simple direct explanation of oxidative phosphorylation.

Ionic partition between surface and bulk water in a silica gel. A biological model

Distribution of the biologically important ions between two aqueous phases of different structure has been used as a model for ionic distribution in living tissue. When other sources of specificity had been eliminated or corrected for, surface-oriented water in a silica gel was found to have increased solvent power for water-structure-breaking ions and decreased solvent power for water-structure-making ions; and the relative solubility of an ion in the phase of enhanced structure increased regularly with the water-structure-breaking powers of the ion. The ionic selectivity was decreased in the presence of urea. The selectivity of the gel water for potassium relative to sodium increased to a maximum when the gel surface was partially ionized so that distribution of cations was not linked to distribution of anions, and then decreased as the surface changed from a hydrogen bonding to an ionic surface. It is pointed out that the distribution of ions across most living cell membranes is qualitatively the same as that found in this silica gel, and it is suggested that the membrane separates two aqueous phases of different structure, and that the enhanced structure of cell water contributes to the observed ionic distributions.