A Mechanistic View of the Non‐ideal Osmotic and Motional Behavior of Intracellular Water

Abstract

It is commonly assumed that essentially all of the water in cells has the same ideal motional and colligative properties as does water in bulk liquid state. This assumption is used in studies of volume regulation, transmembrane movement of solutes and electrical potentials, solute and solution motion, solute solubility and other phenomena. To get at the extent and the source of non-ideally behaved water (an operational term dependent on the measurement method), we studied the motional and colligative properties of water in cells, in solutions of amino acids and glycine peptides whose surface characteristics are known, and in solution of bovine serum albumin, hemoglobin and some synthetic polypeptides. Solutions of individual amino acids with progressively larger hydrophobic side chains showed one perturbed water molecule (structured-slowed in motion) per nine square angstroms of hydrophobic surface area. Water molecules adjacent to hydrophobic surfaces form pentagonal structural arrays, as shown by X-ray diffraction studies, that are reported to be disrupted by heat, electric field, hydrostatic pressure and phosphorylation state. Hydrophilic amino acids demonstrated water destructuring (increased motion) that was attributed to dielectric realignment of dipolar water molecules in the electric field between charge groups. In solutions of proteins, several methods indicate the equivalent of 2-8 layers of structured water molecules extending beyond the protein surface, and we have recently demonstrated that induced protein conformational change modifies the extent of non-ideally behaved water. Water self-diffusion rate as measured in three different cell types was about half that of bulk water, indicating that most of the water in these cells was slower in motion than bulk water. In different cell types the extent of osmotically perturbed water ranged from less that half to almost all of the intracellular water. The assumption that essentially all intracellular water has ideal osmotic and motional behavior is not supported by the experimental findings. The non-ideally of cell water is an operational term. Therefore, the amount of non-ideally behaving water is dependent on the characteristics of water targeted, i.e. the measurement method, and a large fraction of it is explainable in mechanistic terms at a molecular level based on solute-solvent interactions.

Monitoring cytotoxic tumour treatment response by diffusion magnetic resonance imaging and proton spectroscopy

“…45 Cytoplasm is highly organized and it is permeated by a dense network of protein filaments, the cytoskeleton. High protein concentration, 46 fibrillary structures and membranous organelles hinder and constrain molecular diffusion. Viscosity of the cytoplasm as determined with electron spin resonance 47 or fluorescence recovery 48 techniques ranges from 2 to 5 cP.…”

“…Prolongation of tumour T 1 and T 2 suggests a parallel gain of water which inevitably will increase water diffusivity. 46 A BT4C glioma line has been extensively used for testing of viral delivery methods for therapeutic genes in our Institute. 12,60,61 This gliosarcoma expands relatively rapidly without microscopic cysts, maintaining adequate perfusion until it occupies a large part of the hemispheric volume.…”

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“…The extent of OUR water in cells has been reported in five vertebrate cell types (Cameron et al 1997, Fullerton et al 2006b, Cameron and Fullerton 2014 and ranges from 1.1 to 2.2 g water per g dry mass. Data in a report by Maric et al (2001) When a known globular protein is dissolved in bulk water the colligative properties of the resulting bulk water solution changes its osmotic pressure, freezing point, boiling point and vapor pressure.…”

Characterization of water of hydration fractions in rabbit skeletal muscle with age and time of post‐mortem by centrifugal dehydration force and rehydration methods

“…This common assumption, either expressed or just tacitly assumed, is that all water above that of this ''bound water'' value has the physical properties of liquid water in bulk. Evidence is mounting to refute this common assumption about the extent of water of hydration on proteins and in cells (Ling, 2001(Ling, , 2004Pollack, 2003;Cameron et al, 1997Cameron et al, , 2007Fullerton and Cameron, 2007).…”