Protein kinase C and simulated ischemia possible aberrations of signal transduction during ischemia

ATP depletion is always associated with prolonged ischemia. It was found that ATP affected calcium- and phospholipid-dependent activation of protein kinase C without hydrolysis of the nucleotide when the activation was monitored by an assay for [3H] 4-beta-phorbol-12, 13-dibutyrate binding activity in a reconstitution system having physiological concentrations of free calcium. When the ATP level was low, an increase in the free calcium concentration could not activate the enzyme. A decrease in pH exacerbated the depressed activation. The concentration of magnesium also affected the activation. On the other hand, free fatty acids, which increase during ischemia, were able to activate the enzyme at a low concentration of ATP in the absence of phorbol ester and phosphatidylserine. These results suggest that calcium- and phospholipid-dependent activation of protein kinase C is suppressed during ischemia, and that fatty acids in turn activate the enzyme. It is possible that ischemia interferes with normal signal transduction via the protein kinase C pathway and causes unusual protein phosphorylation.