Tissue water and electrolytes in an isolated perfused rat's heart preparation.

An apparatus and technique for perfusion of rats' hearts is described. At 27°C hearts beat spontaneously, and the preparation is stable for periods in excess of 12 hours as judged by heart rate, EKG configuration, force of contraction, pH of perfusion medium and intracellular potassium. Carbon-14 labeled sucrose has been compared with chloride as a measure of tissue extracellular space and has been found unsatisfactory because volume of distribution for carbon-14 is larger than for chloride in most experiments. Carbon-14 labeled inulin-carboxylic acid (ICA), in contrast, appears to be a satisfactory marker for extracellular space. Distribution of ICA is complete in 1 hour. Values for intracellular electrolytes and water, derived assuming extracellularity of ICA, are: water, 2.56 α 0.14 gm/gm dry tissue; Na+ 24.36 α 14.12 mEq/kg cell water or 6.18 α 3.53 mEq/100 gm dry tissue; Cl- 23.16 α 6.70 mEq/kg cell water or 5.96 α 1.93 mEq/100 gm dry tissue; and K+ 144.69 α 7.31 mEq/kg cell water or 36.99 α 1.55 mEq/100 gm dry tissue. Chloride is not a satisfactory measure of extracellular space in the isolated perfused rat heart. Submitted on July 20, 1960