Transport phenomena, biological systems

The osmosis phenomenon, stemming from biological systems with biological semipermeable membrane, initially represents a nature net transport of solvent molecules from a region of higher water chemical potential (e.g., dilute solution) to a region of lower water chemical potential (e.g., concentrate solution). The driving force is the pure chemical potential difference, i.e., osmotic pressure difference, across the membrane. 

A mixed-film phenomenon of particular interest in the biological and medical areas is that referred to as film penetration, in which a soluble surface-active material in the substrate enters into the surface film in sufficient quantity to alter its nature significantly, or to undergo some alternative physical or chemical process related to the surface (Fig. 8.20). Such penetration studies using films of biological materials have been used to mimic phenomena in biological systems (cell walls and membranes, for example) that cannot readily be studied directly. Of particular interest are such topics as cell surface reactions, catalysis, and transport across membranes. 

The solubilization phenomenon, which refers to the dissolution of normally insoluble or only slightly soluble compounds in water caused by the addition of surfactants, is one of the most striking effects encountered for surfactant systems. Solubilization is of considerable physico-chemical interst, such as in discussion of the structure and dynamics of micelles and of the mechanism of enzyme catalysis, and has numerous practical applications, such as in detergency, in pharmaceutical preparations and in micellar catalysis. In biology, solubilization phenomena are most significant, e.g., cholesterol solubilization in phospholipid bilayers and fat solubilization in fat digestion and transport. 

The phenomenological description of the excitability phenomenon given in Section 1.3 cannot claim to contain a final solution to the problem of the nature of transport systems of biological membranes responsible for nervous impuse generation. Where we stand, we can only conclude that the membrane as a whole is a nonlinear ion conductor whose properties are largely dependent upon the electrice field. For all that, the fact that the use of certain specific blocking compounds—tetrodotoxin and tetraethylammonium—allows the sodium and potassium ionic currents to be separated is alone sufficient to support the conception of selective transport systems located in the lipid matrix... 

The proton flux mediated electro-osmosis or in short proto-osmosis is the perimembrane and transfilament analog of Mitchell s (transmembrane) chemiosmotic theory and could be operating at the cellular and organismal levels in diverse dynamical processes (see Transport in Plants, Chapter 21 in this volume). If the phenomenon is experimentally verified in muscles and in other systems, the dynamic aspects of cell biology would become amenable to quantitative treatment using the principles of electrochemistry. 

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