  We consider a charged Brownian particle in an asymmetric bistable
electrostatic potential biased by an externally applied or induced time
periodic electric field. While the amplitude of the applied field is
independent of frequency, that of the one induced by a magnetic field is.
Borrowing from protein channel terminology, we define the open probability as
the relative time the Brownian particle spends on a prescribed side of the
potential barrier. We show that while there is no peak in the open probability
as the frequency of the applied field and the bias (depolarization) of the
potential are varied, there is a narrow range of low frequencies of the induced
field and a narrow range of the low bias of the potential where the open
probability peaks. This manifestation of stochastic resonance is consistent
with experimental results on the voltage gated Iks and KCNQ1 potassium channels
of biological membranes and on cardiac myocytes.
