Electron probe analysis of sodium and other elements in hypertrophied and sodium-loaded smooth muscle

The composition of normal, hypertrophied, or sodium-loaded rabbit portal anterior mesenteric vein and of normal and sodium-loaded guinea pig taenia coli smooth muscle was measured in cryosections with electron probe analysis, and the effects of wash with cold sodium-free (Lithium) solutions were determined. There was no significant difference in the cytoplasmic, nuclear, or mitochondrial concentrations of any of the measured elements (sodium, potassium, chloride, magnesium, calcium, phosphorus, sulfur) between hypertrophied, sham-operated, or control veins. The cytoplasmic potassium:sodium:chloride ratio in rabbit portal anterior mesenteric vein was 1:0.26:0.46, and the average sodium concentration (198 mmol/kg dry cytoplasmic weight) was nearly twice as high as estimated from ion flux measurements. The cytoplasmic sodium concentration of normal guinea pig taenia coli was 61 mmol/kg dry weight. The existence of a rapidly exchanging, relatively low affinity, and temperature-insensitive component of cytoplasmic sodium efflux was indicated by the reduction in cytoplasmic sodium after washout in cold, sodium-free (lithium or Tris-substituted) solutions. This reduction, by 62% in normal, 71% in sodium-loaded portal anterior mesenteric vein, and 36% in sodium-loaded guinea pig taenia coli smooth muscle, suggests that the lithium wash method can underestimate cell sodium. In sodium-loaded guinea pig taenia coli and portal anterior mesenteric vein smooth muscles, the cytoplasmic sodium analyzed in individual cells showed a bimodal distribution; in cryosections, the cells having the highest sodium and lowest potassium and phosphorus content also had a more electronlucent (light cell) appearance.