Objective    To investigate the effect of calcium/calmodulin-dependent protein kinaseⅡ (CaMKⅡ) inhibitor

KN93 on calcium overloading of atrial muscle cells in neonatal rats and detect the expression of CaMKⅡ.     Methods    The atrial muscle cells from neonatal rats were primarily cultured for 96 h and then divided into 6 group

control

cal

cium overloading group

KN93 group (0.5 μmol/L)

low-

moderate- and high-dose of KN93+ calcium overloading group. A model of calcium overloading for atrial muscle cells was established by using calcium ionophore (ionomycin

1.0 μmol/L). For the later 3 groups

KN93 at doses of 0.25

0.5 and 1.0 μmol/L was added into the culture medium for 30 min followed by 1.0 μmol/L ionomycin treatment for another 30 min. The identification of α-actin was performed by immunofluorescence staining. In the present of Fluo-3/AM (an indicator of calcium)

intracellular calcium and the expression of CaMKⅡ were detected under the intervention of KN93 with laser cofocal microscopy and Western blotting respectively.     Results    More than 90% of cultured cells were positive to αactin antibody. Compared with the control group

the fluorescence intensity of intracellular Ca

2+

was increased significantly by ionomycin (660.16±108.47 vs 376.12±57.57

P0.01)

but KN93 alone had no effect on it (389.00±64.01

P0.05). In presence of KN93 pretreatment (0.25

0.5 and 1.0 μmol/L)

the fluorescence intensity of intracellular Ca

2+

induced by ionomycin was significantly decreased (558.00±102.56

499.58±64.99

494.25±78.77 vs 660.16±108.47

P0.01). The expression of CaMKⅡ was increased in calcium overloading group compared with control (P0.01) and KN93 alone had no effect on it. But KN93 pretreatment significantly reduced the expression of CaMKⅡ compared with in cells of calcium overloading group (P0.01).     Conclusion    KN93

an inhibitor of CaMKⅡ

can reduce the calcium loading of atrial muscle cells induced by ionomycin

and downregulate the expression of CaMKⅡ.