A Microperfusion Study of Bicarbonate Accumulation in the Proximal Tubule of the Rat Kidney

In order to determine whether HCO₃^- gains access to the proximal tubular lumen from a source other than the glomerular filtrate, we carried out microperfusion experiments on isolated segments of rat proximal tubules in vivo. The perfusion fluid was essentially free of HCO₃^- and of a composition that prevented net absorption of sodium and water.