Principles of Cell Volume Regulation

Abstract

Cell volume is determined by the content of osmotically active solute (cell osmoles) and the osmolarity of the extracellular fluid. Cell osmoles consist of non-diffusible and diffusible solutes. A large fraction of the diffusible cation content balances negative charges on the non-diffusible solutes. The content of diffusible solutes is determined by the electrochemical gradients driving them across the plasma membrane and the availability and activity of transport pathways in the membrane. The classical view that the sodium pump offsets passive leaks must be modified to accomodate the contributions of a number of secondary active transport processes, as well as to allow for changes in cell nondiffusible osmoles and in their net negative charge. The behaviour of cells in anisosmotic media is often different from that predicted for a perfect osmometer. In many cases this is a consequence of changes in cell osmole content. However, caution is required in extrapolating from in vitro responses of isolated cells to large, acutely induced changes in medium osmolality to the responses of tissues in vivo to more subtle changes in extracellular osmolality.

Cell shrinkage and apoptosis: a role for potassium and sodium ion efflux

“…Several studies have demonstrated that alterations in the activity of the Na + , K + -ATPase pump are associated with adverse effects on intracellular sodium concentration gradients and cell volume. In the absence of pump activity, the transmembrane sodium gradient dissipates and the cell eventually swells due to the presence of non-diffusible intracellular macromolecules (Macknight, 1988) while [Na + ] i decrease and cell volume decreases in response to elevated pump activity. As determined by flow cytometry, we demonstrate that following UV-irradiation, apoptosis associated cell shrinkage is accompanied by a parallel decrease in [Na + ] i ( Figure 6).…”

Rate of neurite outgrowth in sympathetic neurons is highly resistant to suppression of protein synthesis: Role of protein degradation/synthesis coupling

“…A major cause of cellular atrophy in all cells is loss of total cellular protein [13]. Therefore, sustained suppression of protein synthesis would cause a net loss of cellular protein and a decrease in cell size if degradation were not also suppressed.…”

COX2 Activity Promotes Organic Osmolyte Accumulation and Adaptation of Renal Medullary Interstitial Cells to Hypertonic Stress

“…Changes in extracellular tonicity typically result in corresponding changes in intracellular solute concentration that allow cells to regain their normal size (1). In renomedullary cells, osmotic equilibrium with elevated extracellular NaCl concentrations is achieved primarily by intracellular accumulation of small organic solutes ("organic osmolytes") (2,3).…”

“…1 Although prostanoid synthesis occurs in all cells and tissues, the kidney is a particularly rich source for prostanoids. Cyclo-oxygenase is a key enzyme regulating the formation of prostaglandins from arachidonic acid, and two isoforms of COX have been identified, a constitutively expressed isoform (COX1) and an inducible isoform (COX2) (6 -8).…”