Bicarbonate reabsorption in the papillary collecting duct: Effect of acetazolamide

The present study was designed to characterize bicarbonate (total CO₂) reabsorption in the papillary collecting duct of the kidney of the Munich-Wistar rat when total CO₂ delivery to this segment was increased by the systemic infusion of a bicarbonate-rich solution. Additional studies examined the effect of the systemic administration of acetazolamide, a carbonic anhydrase inhibitor, on total CO₂ reabsorption. Employing free-flow micropuncture techniques, tubular fluid samples were obtained from the base and tip of the exposed papilla and subsequently analyzed for total CO₂ and inulin. Total CO₂ reabsorption increased in a linear fashion, approximately 34% of that delivered to the base, as total CO₂ delivery increased from 3 to 20% of the filtered load. When examined at comparable absolute rates of total CO₂ delivery (μmol/min) to the papillary collecting duct, acetazolamide administration resulted in marked inhibition of total CO₂ reabsorption. The results of these studies suggest that the papillary collecting duct of the rat kidney possesses a significant capacity for reabsorption of total CO₂ and that this reabsorption is diminished by the administration of acetazolamide.