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RECEPTORS AND SIGNAL TRANSDUCTION

Role of protein kinase C- in the age-dependent secretagogue action of bile acids in mammalian colon

¹Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand; and ²Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois

Submitted 14 May 2007 ; accepted in final form 24 September 2007

The role of specific PKC isoforms in the regulation of epithelial Cl^– secretion by Ca²⁺-dependent secretagogues remains controversial. In the developing rabbit distal colon, the bile acid taurodeoxycholate (TDC) acts via intracellular calcium to stimulate Cl^– transport in adult, but not in young, animals, whereas the PKC activator phorbol dibutyrate (PDB) stimulates Cl^– transport at all ages. We tested the hypothesis that specific PKC isoforms account for the age-specific effects of TDC. The effects of conventional (cPKC) and novel (nPKC) PKC-specific inhibitors on TDC- and PDB-stimulated Cl^– transport in adult and weanling colonocytes were assessed by using 6-methoxy-quinolyl acetoethyl ester. In adult colonocytes, the cPKC inhibitor Gö-6976 inhibited PDB action but not TDC action, whereas the cPKC and nPKC inhibitor Gö-6850 blocked both TDC and PDB actions. Additionally, rottlerin and the PKC--specific inhibitor peptide (V1-1) inhibited TDC- and PDB-stimulated Cl^– transport in adult colonocytes. Rottlerin also decreased TDC-stimulated short-circuit current in intact colonic epithelia. Only Gö-6976, but neither rottlerin nor V1-1, inhibited PDB-stimulated transport in weanling colonocytes. Colonic lysates express PKC-, -, and - protein equally at all ages, but they do not express PKC- or - at any age. Expression of PKC-β and PKC- protein was newborn>adult>weanling, whereas PKC- was expressed in adult but not in weanling or newborn colonocytes. TDC (1.6-fold) and PDB (2.0-fold) stimulated PKC- enzymatic activity in adult colonocytes but failed to do so in weanling colonocytes. PKC- mRNA expression showed age dependence. Thus PKC- appears critical for the action of TDC in the adult colon, and its low expression in young animals may account for their inability to secrete in response to bile acids.

epithelial chloride transport; taurodeoxycholate; signal transduction