The handler function for an item can be used to write the mouseclick event logic.
columns: [
{
xtype:'actioncolumn',
header: "Action",
width:55,
items: [{
icon:'{!$Resource.Images}/Image.png',
tooltip: 'Configure Kit',
id:'ImageId',
style: {
marginLeft: '5px'
},
handler: function(grid, rowIndex, colIndex) {
var rec = grid.getStore().getAt(rowIndex);
// Do the click event logic here
}
}]
]