Gas turbine with a cooled turbine stage and method for cooling the turbine stage

The turbine (1) has a cooling medium feed device for feeding cooling medium i.e. air, into the interior of a guide vane (11) of a turbine stage (8) for cooling the guide vane. A rear edge (16) of the guide vane at a pressure side (18) is provided with a cooling medium outlet opening (25) for discharging the cooling medium out of the guide vane into a main flow. The feed device has a mass flow control device (20) i.e. throttle valve, for increasing the mass flow through the outlet opening during a partial-load operation of the turbine compared to that during a full load operation. An independent claim is also included for a method for cooling a turbine stage of a gas turbine.