Regional differences in the histochemical localization of carbonic anhydrase in the midgut of tobacco hornworm (Manduca sexta)

✍ Scribed by Ridgway, Richard L. ;Moffett, David F.

• Publisher: John Wiley and Sons
• Year: 1986
• Tongue: English
• Weight: 673 KB
• Volume: 237
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402370313

✦ Synopsis

Carbonic anhydrase (CAI activity was assayed by a histochemical method in mounted cryostat sections of larval midgut of Munducu sextu (Insecta: Sphingidae). In anterior and middle midgut most CA activity was associated with apical microvilli of goblet cells; with occasional patchy staining of the columnar cell brush border in anterior midgut. In contrast, in the posterior midgut, the apical microvilli of goblet cells showed no CA activity, but intense staining was associated with the brush border of columnar cells. Staining of mitochondria and nuclei was seen in all midgut regions. In addition, midguts from late fifth instar larvae showed intense staining of spherites (mineral concretions). Acetazolamide (10-5M) completely inhibited staining at all sites except nuclei and spherites. Thiocyanate (100 mM) completely inhibited staining at all sites except anterior and middle goblet cell microvilli, which remained partially reactive. These results suggest that the anteriormiddle and posterior regions play different roles in generating and managing the alkalinization of midgut contents characteristic of lepidopteran midgut. The different sensitivities of CA activity in anterior-middle and posterior midgut to thiocyanate raises the possibility that more than one form of the enzyme may be involved.

The midgut of lepidopteran larvae maintains substantial gradients of K + and pH across its single layer of epithelial cells. The pH gradient is roughly 4.5 pH units (Dow, '841, while the K+ gradient may approach ten-fold for leaf-fed animals and two-fold for artificial diet-fed animals (Jungreis et al., '73). Two main cell types, goblet and columnar cells, comprise the midgut epithelium (Anderson and Harvey, '66). Basal regenerative cells are also present in some species. Much evidence (reviewed by Harvey et al., '83) suggests that oblet cells possess an api-