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J Appl Physiol 60: 646-652, 1986;
8750-7587/86 $5.00
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Journal of Applied Physiology, Vol 60, Issue 2 646-652, Copyright © 1986 by American Physiological Society

ARTICLES

Carbonic anhydrase: inhibition results in decreased urea production by hepatocytes

S. J. Dodgson and R. E. Forster 2nd

The amount of urea produced in 60 min, [urea]t = 60, from intact guinea pig hepatocytes incubated in NH4Cl, oleate, lactate, NaHCO3, and ornithine at 37 degrees C at pH 7.1 is decreased by ethoxzolamide (EZ): Ki,EZ [urea]t = 60 +/- SD at 37 degrees C, pH 7.1 is 0.14 +/- 0.11 mM (10 Dixon plots). This value is in the same range as Ki,EZ for carbonic anhydrase (CA) activity of disrupted hepatocytes at 37 degrees C: 0.08 +/- 0.06 mM (2). [Urea]t = 60 is pH dependent whether external CO2 is supplied (25 mM HCO-3, 95% O2-5% CO2 and 5 mM HCO-3, 99% O2-1% CO2) or not [20 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), 100% O2]. Ki,EZ [urea]t = 60 is independent of both external pH and external total CO2. Ki,EZ (CA) of disrupted mitochondria at 37 degrees C is 0.033 +/- 0.013 microM (2). This value was approximately 3,000-fold lower than the Ki,EZ [urea]t = 60 for intact hepatocytes or Ki,EZ (CA) for disrupted hepatocytes. These results support the general hypothesis that mitochondrial CA is involved in urea synthesis by intact hepatocytes and that cytosolic components raise the experimentally determined Ki,EZ [urea]t = 60. We also conclude that the value of Ki,EZ [urea]t = 60 is independent of the availability of the substrate HCO-3 from external sources.


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C. Geers and G. Gros
Carbon Dioxide Transport and Carbonic Anhydrase in Blood and Muscle
Physiol Rev, April 1, 2000; 80(2): 681 - 715.
[Abstract] [Full Text] [PDF]


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