  This paper applies the isotopic field-charge spin theory (Darvas, IJTP 2011)
to the electromagnetic interaction. First there is derived a modified Dirac
equation in the presence of a velocity dependent gauge field and isotopic field
charges (namely Coulomb and Lorentz type electric charges, as well as
gravitational and inertial masses). This equation is compared with the
classical Dirac equation. There is shown that, since the presence of isotopic
field-charges would distort the Lorentz invariance of the equation, there is a
transformation, which together with the Lorenz transformation restores the
invariance of the equation, in accordance with the conservation of the isotopic
field-charge spin (Darvas, 2009). The paper discusses the conclusions derived
from the extensions of the Dirac equation. It is shown that in semi-classical
approximation the model provides the original Dirac equation, and at
significantly relativistic velocities it approaches to the Schr\"odinger
equation. Among other conclusions, the clue gives physical meaning to the
electric moment. The closing section summarises a few further conclusions and
shows a few developments to be discussed in detail in a next paper (Darvas,
2013).
