STEADY-STATE MAINTENANCE OF ELECTROLYTES IN THE SPINAL-CORD OF THE FROG

Isolated frog [Rana pipiens] spinal cords equilibrated from 3-24 h in Ringer''s solution maintained steady state conditions with regard to electrolyte composition. Total Na and Cl- contents measured on the same spinal cords were nearly equivalent (Na = 46.6 .+-. 1.4 .mu.mol/g wet wt vs. Cl- = 46.2 .+-. 1.2 .mu.mol/g wet wt). Ca and Mg contents were 3.0 .+-. 0.5 and 4.8 .+-. 0.2 .mu.mol/g wet wt, respectively, for fresh spinal cords and 2.1 .+-. 0.4 and 5.5 .+-. 0.9 .mu.mol/g wet wt, respectively, for spinal cords equilibrated for 24 h. Zn content was 0.26 .+-. 0.01 .mu.mol/g wet wt. Insulin space was smaller than sucrose space (0.24 ml/g vs. 0.37 ml/g). Na and Cl- spaces were slightly higher than sucrose space. Na and Cl- in the non-sucrose space was 4.8 and 9.5 .mu.mol/g wet wt. Residual radioactive Na, or Na content of spinal cords washed out for 180 min in non-radioactive Ringer''s solution or in choline or Li Ringer''s solution was 4.2 .+-. 0.4 .mu.mol/g wet wt (n = 9). The agreement between residual Na content and Na in the non-sucrose space suggests that the mean intracellular Na content of the spinal cord neurons is low.