How did the soviets respond when french britain and united states combined their german zones of occupation into one nation?

The Soviets responded by blockading Berlin, preventing all traffic (military, passenger, shipping) by the Allies (US, France, Britain).

When the British, French and American authorities combined their zones of control into a unified West Germany and West Berlin, the Soviets established what has become known as the Berlin Blockade.  The western Allies responded with the Berlin Airlift, dropping supplies into Berlin via cargo planes to maintain the western portion of the city as separate from Soviet control.