Effects of Experimental Ischemia on Expression of Protein Kinase C Isozyme in Rat Neocortex

ABSTRACT

Ischemia leads to a complex sequence of events culmination in the loss of functional integrity of the nervous system and, ultimately, in neuronal cell death. Intracellular accumulation of calcium ions following ischemia may alter protein kinase C(PKC) activity. But nature of change of the PKC activity depending on duration and degree of ischemia is not well understood. To understand the effect of the experimental focal ischemia on expression of PKC isozyme, we investigated the expression of PKC gamma, beta, alpha immunocytochemically and activities of cytochrome oxidase(CO) histochemically in focal ischemic brain of the rat. Two groups of focal ischemic infarction were produced in two groups of Sprague Dawley rats(200-300 gm) Group I, Clip compression of left middle cerebral artery(MCA) for 10min and releases and sacrificed 48 hr later ; Group II, Electric coagulation of left MCA and killed 2-24 hr later. In the group I, CO activity and immunoreactivity(IR) for PKC gamma and beta were decreased generally in the left MCA territory, especially in layers II through IV of ischemic cortex. In the group II, decrease of CO activities and marked increase of three PKC isozyme IRs were noted in the layers I through IV. The isozymes displayed different localization in the control cortex, but the IRs of three isozymes markedly increased in the ischmic region, so that the difference among IR patterns disappeared. Although vacuolation and decrease of number of IR neuron were noted, there were remaining IR pyramidal neurons arounf vacuole in layers IV/V showing dense immuostaining in the cell body and apical dendrite. These results indicate that 10min acute ischemia inhibits activity of PKC gamma and beta and that prolonged ischemia longer than 2hr induces the expression of three PKC isozymes. Inhibition and possible induction of PKC are proposed to represent a critical step during ischemic neuronal injury.