Change android camera's iso value after startPreview()

Question

1. Camera.open();
2. Get parameters of camera and set iso value 100 (default value was "auto")
3. set parameters to camera
4. camera.startPreview();
5. camera's iso value is 100 at this time. It works fine.
6. change the iso value to 400, and iso value is shown well as I expected. ("iso = 400")

7. but preview image has not changed at all.. <---- image must be brighten! but nothing has been changed..

Is there a way to change iso value after start preview?

autoWhitebalanceLock = true, autoExposureLock = true, exposureCompenstation value was fixed to 0..