OBJECTIVETo observe the alteration of cardiac myocyte nuclear inositol 1,3,4,5-tetrakisphosphate receptor (IP(4)R) binding properties in rat subjected to myocardial ischemic reperfusion in order to further make it clear whether this change is involved in the molecule mechanism of cell apoptosis of rat with myocardial ischemic reperfusion.

METHODSExtracting of cardiac myocyte nucleus was accomplished by saccharose density gradient centrifugation method, the binding properties of nuclear IP(4)R in different conditions were detected by radioligand binding assay. Apoptosis index of myocardial cell was determined by using TUNEL assay.

RESULTS(1) Myocardial cell apoptosis index in rat heart underwent 30 min regional ischemia and 3 h reperfusion increased distinctly compared with that in control group (P < 0.01). (2) There were two IP(4) binding sites located to the nuclear envelope. (3) In ischemic reperfusion injury (IRI) group, Bmax from high affinity binding site of nuclear IP(4)R significantly increased compared with that in sham-operated group, whereas Bmax from low affinity binding site didn't change. Kd values of both sites were all significantly decreased by 63% and 55%, respectively. (4) Phosphorylation of nuclear IP(4)R by PKC increased markedly its binding ability both in IRI and control group (P < 0.05), which was more apparent in IRI group. (5) In sham-operated group, the binding ability of nuclear IP(4)R increased with increasing free calcium concentrations in cytoplasm, and the binding properties of IP(4)R in IRI group were also increased in the condition of calcium overloading.

CONCLUSIONThe increasing of binding properties of nuclear IP(4)R from ischemic reperfusion heart may be one of important mechanism involved in myocardial cell apoptosis, furthermore resulting in myocardial IRI.