When you wish to have variables that have an scope (that means that are "visible") in all functions of the GUI, you should store them in handles. handles is an structure, so you should need something like this:
% Callback 1
% Retrieve GUI data (the handles structure)
handles = guidata(hObject)
% ...
handles.y = 1:10; % Load the data from the .mat file here
% ...
% Update handles structure
guidata(hObject, handles);
% Callback 2
% Retrieve GUI data (the handles structure)
handles = guidata(hObject);
% ...
handles.x = handles.y .* 3; % Do whatever you want with the "y" data here
% ...
% Update handles structure
guidata(hObject, handles);
The handles = guidata(hObject); and guidata(hObject, handles); lines are important because you need them to keep the GUI "updated".
Hope it helps ;-) .
