plpgsql (postgresql 8.3 but I can upgrade)

I can open a cursor with a dynamic query (table / column variable) :
-open cursor for execute '...' ;
But if I want do updates...
- execute 'update ...' where current of cursor ??
Mmm I don't find the way.

Another approach :

-execute 'declare cursor ...' +with hold -for update :(
-execute 'update ... where current of cursor'...