Ca2+-independent protein kinase C isoforms may modulate parietal cell HCl secretion

Am J Physiol. 1997 Feb;272(2 Pt 1):G246-56. doi: 10.1152/ajpgi.1997.272.2.G246.


Although activation of adenosine 3',5'-cyclic monophosphate by histamine and of Ca2+-dependent signaling pathways by cholinergic agonists is a generally recognized mechanism for increasing parietal cell HCl secretion, the role of protein kinase C (PKC) in this process is controversial. In this study, acid-secretory responses of gastric glands from rabbits [measured as accumulation of aminopyrine (AP)] were found to be relatively resistant to the PKC inhibitors calphostin C, chelerythrine chloride, staurosporine, and the bisindolylmaleimide-like inhibitors Ro 31-8220, Gö 6976, and bisindolylmaleimide I hydrochloride. Western analyses of the PKC isozyme profile in highly enriched parietal cells (98% purity) indicated that this cell type expresses abundant levels of the novel isoforms PKC-epsilon and PKC-mu and abundant levels of the atypical isoforms PKC-iota, PKC-lambda, and PKC-zeta. In contrast, there appeared to be low to undetectable expression of the classical isoforms PKC-alpha and PKC-beta1/beta2, respectively. Relatively high concentrations of Ro 31-8220 potentiated both carbachol- and histamine-stimulated AP accumulation (IC50 857 +/- 100 and 910 +/- 98 nM, respectively). There was a similar dose dependence for Ro 31-8220 inhibition of in situ phosphorylation of a parietal cell phosphoprotein, pp66 (IC50 750 +/- 120 nM). Similar concentrations of Ro 31-8220 also inhibited phosphorylation of the cytoskeletal, actin membrane cross-linking phosphoprotein ezrin, but not other phosphoproteins. Ezrin phosphorylation was increased by carbachol and 12-O-tetradecanoylphorbol 13-acetate (TPA). Because carbachol and TPA stimulate pp66 phosphorylation in a Ca2+-independent manner, our results suggest that one or more novel PKC isoforms may be involved in negative regulation of HCl secretion. In related experiments, PKC-epsilon, but not PKC-mu, was immunolocalized by confocal microscopy to a parietal cell compartment that bore a striking resemblance to that containing filamentous actin. Moreover, pp66 was enriched in a Triton X-100-insoluble parietal cell fraction, suggesting a potential cytoskeletal localization for this unknown protein. Given their location and sensitivity to Ro 31-8220, it is possible that pp66 and ezrin interact in a PKC-dependent manner to regulate the well-known morphological changes that occur in concert with agonist-dependent activation of parietal cell HCl secretion.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actins / metabolism
  • Aminopyrine / metabolism
  • Animals
  • Calcium / physiology*
  • Cytoskeletal Proteins
  • Cytoskeleton / metabolism
  • Enzyme Inhibitors / pharmacology
  • Fluorescent Antibody Technique
  • Hydrochloric Acid / metabolism*
  • Indoles / pharmacology
  • Isoenzymes / physiology*
  • Male
  • Parietal Cells, Gastric / metabolism*
  • Phosphoproteins / metabolism
  • Phosphorylation / drug effects
  • Protein Kinase C / antagonists & inhibitors
  • Protein Kinase C / physiology*
  • Rabbits
  • Subcellular Fractions / metabolism
  • Time Factors


  • Actins
  • Cytoskeletal Proteins
  • Enzyme Inhibitors
  • Indoles
  • Isoenzymes
  • Phosphoproteins
  • ezrin
  • Aminopyrine
  • Protein Kinase C
  • Hydrochloric Acid
  • Calcium
  • Ro 31-8220