Having equal tension or tonicity
Isotonic is a descriptive word relating to isotonicity. In cellular level, isotonicity may pertain to a property of a solution in which its solute concentration is the same as the solute concentration of another solution with which it is compared. Thus, a solution is described as isotonic when the other solution being compared with have the same (or equal) osmotic pressure and same water potential since the two solutions have an equal concentration of water molecules. It may also pertain to a condition or property of a solution that has the same tonicity as the other solution with which it is compared. For example, blood serum is isotonic to a physiologic salt solution. Solutions that have same tonicity will result in no net flow of water across the cell membrane
In tissue level, isotonicity is defined as a condition in which the muscle remains to be in a relatively constant tension while its length changes. In particular, the term isotonic muscle pertains to a muscular contraction in which the muscle remains to be in a relatively constant tension while its length changes.
Word origin: iso– + Greek tonos (“tension”) + –ic