Specialized function of carbonic anhydrase-rich and granular cells of turtle bladder

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Abstract
The mucosal surface of the turtle bladder consists of two major cell types, carbonic anhydrase-rich (CA) and granular (G) cells. These cells types may have specific transport functions. To separate and study these cells, they were removed from the bladder by collagenase digestion and then separated into two distant subpopulations by Ficoll discontinuous density-gradient centrifugation. By morphological criteria the lighter subpopulation (band II) consists primarily of CA cells and the denser population (band III) G cells. The distribution of two enzymes important for H+ transport, CA and glucose-6-phosphate dehydrogenase (G-6-PD), and the effect of specific transport inhibitors, acetazolamide and ouabain, on O2 consumption of these cells was examined. The CA activity of band II cells was 4.5 times greater than that of band III cells. The G-6-PD activity of band II cells was 2.2 times greater than that of band III cells. The rate of O2 consumption of band II cells, 4.73 microliters.mg protein-1.h-1, was reduced 40% by 5 X 10(-5) M acetazolamide but not by ouabain. Band III O2 consumption, 3.43 microliters.mg protein-1.h-1, was reduced 30% by 10(-4) M ouabain but not by acetazolamide. On the basis of the distribution of CA and G-6-PD and the effect of acetazolamide and ouabain on O2 consumption, we propose that CA cells are primarily responsible for H+ transport and G cells for Na+ transport.