Effects of metabolic inhibition on phosphorylation levels of PKC isoforms in the guinea pig taenia caeci

Abstract

We investigated which isoform of protein kinase C (PKC) is responsible to metabolic inhibition in the guinea pig taenia caeci with respect to their phosphorylation levels. By Western blot analysis using isoform-specific antibodies, at least four isoforms of PKC, α, β2, ε and ζ were identified in the taenia. Prolonged metabolic inhibition of hypoxia, hypoxia+glucose depletion, and addition of cyanide (all in the presence of high K⁺) for more than 60 min, but not glucose-depletion only, elicited dephosphorylation of PKCs, α, β2 and ε, except ζ. Ca²⁺ depletion from the medium prevented the dephosphorylation of PKCs induced by hypoxia, and apparently inhibited the dephosphorylation induced by hypoxia+glucose depletion. Acute treatment with hypoxia for 10-30 min elicited a gradual dephosphorylation of PKCβ2, but not of other tested PKC isoforms. Considering the ATP level under various metabolic conditions reported previously, PKCβ2 is suggested to be primarily responsible to hypoxia, and its dephosphorylation is closely associated with the alteration of adenylate compounds in the cell. Re-oxygenation after prolonged hypoxia did not restore the phosphoryation level of any tested PKCs, suggesting that the dephosphorylation of PKCs is associated with the irreversible damage of the cell under hypoxia. Presumably, the dephosphorylaton of PKCs, particularly PKCβ2, plays a role in the signal transduction pathway under metabolic inhibition of the taenia, as reported in proliferative and pathophysiological processes in many other cells.