Abstract
Intra-and extracellular sodium in guinea pig erythrocytes was evaluated with sodium-23 nuclear magnetic resonance (23Na-NMR) by the use of a shift reagent, Dy (TTHA) 3-or Dy (PPPi)27-. The test medium contained erythrocytes at 40% hematocrit level and NMR buffer (145 mM NaCl, 10 mM Dy (T-THA) 3-, 10% D2O, adjusted to pH 7. 4 with tris, at 35°C). NMR spectra were obtained with a JEOL GSX 400 spectrometer operating at the Fourier transform mode of resonance signals, and the accumulated signals provoked by radio-frequency pulses of 90° were recorded on paper. Quantitative Na determination was performed by measuring the area under the peak of intracellular sodium (Nai) NMR signals. Ouabain (Oua : 0.3 mM) and asebotoxin-III (ATX-III : 0.3 mM) produced an increase in NaiNMR signals to a level of 188. 1% and 138. 1% of the control, respectively. Combined use of Oua (0.15 mM) and ATX-III (0.15 mM) produced an elevation of Nai concentration to a high level of 219.0% of the control in a superadditive manner. Mechanisms of the Nai elevation with Oua and ATX-III can be interpreted by assuming two different actions : ATX-III increases net Na+-influx via Na+ channels, while Oua inhibits the pumping out of Na+from the cell.
