A potassium gradient in smooth muscle segment of the opossum esophagus.

Sodium and potassium content were determined in the smooth muscle segment of the opossum esophagus. Extracellular space measurements were also made using inulin and mannitol as markers. The muscle also made using inulin and mannitol as markers. The muscle was sampled at five sites spaced equally along the esophageal segment. On site in the stomach was also examined. The mean tissue sodium content was 36.6 +/- 10.7 meg/kg, and the mean tissue sodium content was 83.5 +/- 2.9 meg/kg wet wt. The mean inulin space was 184 +/- 34 ml/kg, and the mean mannitol space was 249 +/- 20 ml wet wt. The tissue potassium content was found to decline from 48.4 /- 10.1 meg/kg at the proximal site to 23.6 +/- 8.0 meg k/g at the distal site. The slope of electrolyte values from sites 1 through 5 was significant for both potassium and sodium. Extracellular space volume did not differ significantly from one end of the smooth muscle segment to the other.