Evidence for the involvement of CaMKII in ischaemic injury

Llwyd, Osian , Prof. Baxter, Gary. Cardiff University Welsh School of Pharmacy, King Edward VII Av, Cardiff, CF103NB, Great Britain.

Cellular stresses such as ischaemia and subsequent reperfusion displace the normal physiological oscillations of Ca2+ to an escalating concentration which consequently damages the cell. Therefore, CaMKII a second messenger to Ca2+ has been implicated as an injury signal during such cellular conditions. However, its inhibition during preconditioning (PC) can abrogate the protective affect. This study investigated CaMKII inhibition either at the onset of reperfusion or before ischaemia in relation to the protective mechanism of PC.

Rat hearts were Langendorff perfused for 20 min before being subjected to 35 min of regional ischaemia, followed by 120 min of reperfusion. A CaMKII inhibitor, KN-93 (2 µM), was administered pre-ischaemia in the presence or absence of a PC stimulus of three, 3 min cycles of ischaemia-reperfusion. Another group received the inhibitor for 5 min at the end of ischaemia and the first 10 min of reperfusion, with and without the PC stimulus. Infarct size (% of risk zone) was determined by vital staining.

Data are mean ± SEM. Under control conditions, infarct size was 41.9±4.6%. PC markedly limited infarct size to 18.8±3.7% (P<0.001 vs control). KN-93 administered prior to ischaemia without PC gave significant protection (17.6±2.9%, P<0.01) and appeared to enhance the protective effect of PC (KN-93 + PC, 10.5±2.5%, P<0.001). When administered only during early reperfusion KN-93 had no effect on infarct size (46.6±4.9%) and did not attenuate the protective affect of PC (22.0±4.2%, P<0.01).

Inhibition of CaMKII with KN-93 before the onset of ischaemia protects against infarct size, suggesting that CaMKII promotes cellular injury during ischaemia as its inhibition during early reperfusion alone was not sufficient to limit injury. However, CaMKII activation is not a pre-requisite for protection with PC. An additive protective effect of CaMKII inhibition and PC is possible.