In this study, a new concept is introduced - gravitational cells. The body of a black hole consists of a huge number of such cells. Based on this hypothesis, using string theory, the Schwarzschild radius formula and the Coulomb formula, a formula for the gravitational constant was obtained. The new formula was used to determine the value of the gravitational constant in the region of black holes, and also confirmed the value of the usual gravitational constant. Also in this work, a new physical constant was obtained - the mass of the gravitational cell of a black hole. The results obtained made it possible to draw conclusions regarding the gravitational mass of the proton and the electron. In this study, the gravity cell hypothesis was organically integrated into string theory. As a result, it was possible to apply the Planck formula to the gravitational interaction. Thus, the formula for the vibration frequency of gravitational strings (the frequency of gravitational waves) was obtained, and their frequency was determined. The formula for the mass of an electron was obtained. The electron mass calculated by the formula coincided with the experimental value.