Chemical and histological space determinations in rabbit heart

¹ Department of Physiology, University of Minnesota Medical School, Minneapolis, Minnesota

The extracellular space of perfused rabbit heart ventricles was estimated by chemical and histological techniques. Sucrose and thiocyanate were used for the chemical space estimations. The method proposed by Chalkley following fixation by freeze substitution was used for the histological extracellular space determination. The extracellular space fraction was altered by using perfusing solutions of different osmotic activity to shrink or swell the cells. The magnitude of the tissue water loss or gain was determined by weighing the heart. Using the assumption that the cells alone changed in volume during an osmotically induced weight change, an alteration in the fractional extracellular space was predicted from the original chemical or histological space determination and the magnitude of the weight change. This predicted change when compared to the observed change in the histological and chemical spaces always agreed in direction with the measured values of both the histological and chemical spaces but was in better quantitative agreement with the values from the chemical technique.