Do something like...

Code:
onItemDisclosure: true,
listeners : {
  itemtap : function(record,index,item,e) {
    if (e.getTarget('.x-list-disclosure')) {
      // do something with the disclosure tap
    } else {
      var currentRecord = record.store.getAt(index);
      App.SomePanel.update(currentRecord.data);
    }
  }
}