Extracellular Na+ electrode for monitoring net Na+ flux in cell suspensions.
A computer-linked extracellular sodium-sensitive electrode system is described that is suitable for the routine measurement of net Na+ transport in cell suspensions. The commercially available Na+ electrode exhibited high selectivity for Na+ over other cations and a rapid response time (less than 3 s). This system resolved changes of 0.4 mM in the presence of 147 mM extracellular Na+. Measurements of Na+ transport in suspensions of rabbit proximal tubules showed that ouabain caused a dose-dependent net Na+ influx with an inhibitor constant (Ki) of 2.5 +/- 0.2 microM and a maximal velocity (Vmax) of 229 +/- 7 nmol Na+.min-1.mg protein-1. This compared favorably with the ouabain-induced K+ efflux (Ki = 2.4 microM; Vmax = 160 +/- 3.3 nmol K+.min-1.mg protein-1) and the ouabain-induced inhibition of respiration (Ki = 3.3 microM; Vmax = 11.8 nmol O2.min-1.mg protein-1). In addition, Ba2+, a K+ channel blocker known to depolarize the cell, caused a net Na+ efflux, whereas glucose, a Na+-cotransported solute, promoted a net Na+ influx. This system should be a powerful tool for continuous monitoring of net Na+ fluxes in cell suspensions.
Brady
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HR
Renal Division, Brigham and Women's Hospital, Boston, Massachusetts 02115.
Kone
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BC
Gullans
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D000818:Animals; D001692:Biological Transport; D004566:Electrodes; D005260:Female; D008991:Monitoring, Physiologic; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D013535:Suspensions
D013535:Suspensions; D012964:Sodium; D011188:Potassium