Selective modulation of PKC isozymes by inflammation in canine colonic circular muscle cells

Background & Aims: Protein kinase C (PKC) is a key signaling molecule in excitation-contraction coupling in several types of smooth muscle cells. We investigated whether the attenuated contraction in inflamed colon cells is caused by alterations in the expression, distribution, and activation of specific PKC isozymes. Methods: Kinase assays, immunofluorescence imaging, and Western immunoblotting were performed on single circular smooth muscle cells obtained from the normal dog colon as well as from colon with experimental colitis induced by mucosal exposure to ethanol and acetic acid, to determine the distribution, expression, and activation of PKC isozymes. Results: Classical (α, β, and γ), novel (δ and ε), and the atypical PKC (ι, λ, and ζ) isozymes were detected in colonic circular muscle cells. The expression of PKC α, β, and ε isozymes was down-regulated, whereas that of PKC ι and λ isozymes was up-regulated; other isozymes were not affected by inflammation. Acetylcholine (ACh) treatment translocated only the PKC α, β, and ε isozymes from the cytosol to the membrane in normal cells; this translocation was absent in inflamed colon cells. Immunofluorescence imaging confirmed the translocation of PKC α from the cytosol to the membrane in response to ACh in normal cells. PKC inhibitors, chelerythrine, and myristoylated peptides to α, β, and ε isozymes inhibited the contractile response to ACh in normal, but not in inflamed, cells. PKC ι and λ did not participate in the contractile response to ACh. Conclusions: ACh-induced contraction is mediated by PKC α, β, and ε isozymes in normal colonic circular muscle cells. Contractile dysfunction in inflamed colon cells is, in part, caused by decreased expression and impaired activation of specific PKC isozymes.