Salinity and Animal Cells

Summary

Biological cells exist in a saline environment which differs in ionic composition from the intracellular solution. Potassium is more concentrated inside, whereas sodium is more concentrated outside, cells. In the resting state, cell membranes are much more permeable to potassium than to sodium ions and this results in an electrical potential across the membrane, negative inside. The transmission of electrical signals, communication between cells, and the conversion of environmental energy to electrical signals, all depend on an inflow of sodium ions into cells as a result of an increase in the sodium permeability of the cell membrane. The intracellular concentrations of sodium and potassium ions are regulated by metabolically ‘fuelled’ ionic pumps. Because membrane potentials are essentially ionic diffusion potentials, the concentration gradients of sodium and potassium ions are of fundamental importance in the generation of electrical signals which are hence very sensitive to the concentration of these ions in the extracellular saline.