Fig. 5. (A–C) Location of carbonic anhydrase (CA) in cryostat sections of salivary gland tubules. The dark reaction product indicating CA activity is localized at the basal pole of the secretory cells as shown in a cross section (B) and a longitudinal section (C). Formation of the reaction product is completely inhibited by 10^–5 mol l^–1 of the CA inhibitor acetazolamide (A). Scale bars, 20 µm.