Two parts of this problem lay in the disciplines of inorganic aquatic chemistry and lipid membrane biochemistry. I have heard that water contained intracellularly is NOT liquid. Also, it is well regulated to maintain the correct cell volume (aquaporin, Na+, K+ and Cl- pumps). Nature won't give up her secrets about the oxirane preferences therein. Not until we completely understand lipid biochemistry will we be able to encompass a definition of cytosol (cf. sol-gel). It was the advantage of early 70's genetics that opened the door to intracellular activity of hormone responses by receptor activation. Receptors are housed in the membrane lipid bilayer completely, partially in or partially out. This was found by mutating amino acids of receptors and looking at effects, after. This opened the door to inside cells! Pharmacology was at a standstill until this point. Most of what we now know has since grown geometrically. Another highlight was the discovery of the "G" protein and then its manifold 'subtypes' which constitute a dominant majority of receptors. The decades of the brain, genome and the like still wait their turn, or pale in comparison. These ALL work together, so it's like an Escher jigsaw puzzle wherein there are only two shapes of white colored pieces. The many have come and gone while Nature, in the form of Man, is beginning to understand itself.

Thanks Steve.  Some good points to ponder.  (your comment, they all work together equates to systems type view which I fully embrace) Questioning the fluidity of the cytosol also taps into an aspect we had been looking at.   My recent efforts have tried to step further upstream to better understand the elemental profiles of the cells.  

The apparent central role of cellular cytosol hasn't been defined. Why? The cell is a water-in-oil emulsion. Perhaps that's why it's called cytosol. Some of the rules from different disciplines apply. Critical micelle concentration; Ionic aquation layers and their reaction constants for hydration or dimerization unto crystallization or polymerization; hydrophilic-hydrophobic interactions; Take Calcium: when allowed inside neurons it wreaks havoc causing a multiciplicity of reactions, that's why it's so tightly controlled. It gets inside by shedding its waters of hydration energetically and in water it can freely have 12 or more waters of hydration. It can bridge-(hydrogen)-bond several other hydrogen bonded nitrogen, oxygen, sulfur or metallic ions. How do you think a functional structure can be sustained? Water is still not that well understood. It can form many cyclic, chained combinations of hydrogen bonded which can, by breaking and making H-bonds rapidly to transfer charges, buffer, redistribute alkalinity & acidity, as well as passing current (von Grotthuss, 1805). There is a lot of organized compartmentalization and routes efficient for flow and bio-reactions. I'm reminded of the Krebbs cycle wherein the proximity of one product exits very near to the next reaction center, like four or five times. It's highly efficient and developed and refined over millenia. I believe that if you could determine the absolute water content of nuclear, lysosomal, mitochondrial and other compartmentalized subcellular structure water contents, and then subtract that sum from the total known average and min. and max. it would define the working volume optimal range limits. Then you could model that volume to work for all of the other typical cell type functions. I would like to see liver (with its manifold mitochondria) and brain cell types or blood cells, fat storage cells, and so forth.