The 'Indirect Sodium-Water Coupling' Hypothesis of Cell Volume Regulation in Cardiac Muscle

摘要

Sodium ion has been traditionally conceived to be the main effector of changes in cellular volumes. Active extrusion of sodium by the Na/K pumps is considered to counterbalance the oncotic pressure of intracellular macromolecules. Development of NMR techniques for non-invasive measurement of cellular sodium and water contents has yielded new insights into cell volume regulation. The "indirect sodium-water coupling" hypothesis postulates that sodium correlates closely to changes in intracellular volume due to its extensive coupling with the transport of osmotically-active ions and molecules. Intracellular sodium and water contents change in parallel, however the coefficients that relate their trans-membranal fluxes in cardiac muscle vary widely. In limited cases, sodium-water uncoupling was observed upon attenuation of intracellular calcium and energy metabolism. This hypothesis offers an alternative mechanistic explanation that underlines the importance of additional volume-regulatory mechanisms bwsides sodium homeostasis.