Evaluating the impact of acetazolamide

The data in table 1 was obtained from the same individual when they had taken acetazolomide (ACTZ), a carbonic anhydrase (CA) inhibitor. CA plays an important role in the reabsorption of HCO^–₃ in the renal proximal tubule. It catalyses the reaction between water and carbon dioxide (Purkerson and Schwartz, 2007^[1]), meaning HCO^–₃ is removed from the filtrate.  Figure 1 shows the cell model.  Filtered HCO^–₃ combines with H⁺, which is lost from the cell in exchange for Na⁺.  This forms carbonic acid, which dissociates into carbon dioxide and water, under the influence of membrane bound CA.  The carbon dioxide diffuses across the apical membrane as it is lipid soluble, while the water enters the cell via aquaporin 1 water channels.  Inside the cell, CA then catalyses the conversion to carbonic acid, which then dissociates into HCO^–₃ and H⁺. The H⁺ recycles across the apical membrane, while the HCO^–₃ moves across the basolateral membrane via the Na⁺-HCO^–₃ cotransporter.  There is therefore reabsorption of both Na⁺ and HCO^–_3, and water as this follows the ions.

Figure 1: a model of HCO^–₃ reabsorption in the renal proximal tubule. NHE3 = Na⁺ and H⁺ exchanger number 3.

Table 1 ACTZ data

Use these data to complete the following questions.  Give all answers to 1 decimal place, and don’t forget to also put the units. Answers should be presented as ml/min, µmole/min or as %, as appropriate.

If you struggled with these questions, go back and review the earlier chapters.