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We study the mechanism of nuclear spin relaxation in quantum dots due to the electron exchange with 2D gas. We show that the nuclear spin relaxation rate T1−1 is dramatically affected by the Coulomb blockade (CB) and can be controlled by gate voltage. In the case of strong spin–orbit (SO) coupling the relaxation rate is maximal in the CB valleys whereas for the weak SO coupling the maximum of 1/T1 is near the CB peaks. The physical mechanism of nuclear spin relaxation rate at strong SO coupling is identified as Debye–Mandelstam–Leontovich–Pollak–Geballe relaxational mechanism.