var RegionsStore = new Ext.data.JsonStore({
                              url:'/mypath/blabla',
                              fields:['Value','Text']
                   });
Ext.onReady(function() {
    Ext.getCmp('ext-Area').on('select', function(sender, item) {
        var target = Ext.getCmp('ext-Regions');
        target.setDisabled(true);
        target.setValue('');
        target.store.removeAll();
        target.displayField = 'Text';
        target.valueField = 'Value';
        target.store = RegionsStore;
        target.store.reload({
               params: {
                  data: 'regions',
                  discriminator: 'area',
                  value: sender.getValue()
               }
        });
        target.setDisabled(false);
    });
});