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We applied a periodic magnetic field of frequency 16 Hz and amplitude 16 nTto a human I_Ks channel, expressed in a Xenopus oocyte and varied the membranedepolarization between -100 mV and +100 mV. We observed a maximal increase ofabout 9% in the potassium current at membrane depolarization between 0 mV and 8mV (see Figure 3). A similar measurement of the potassium current in the KCNQ1channel, expressed in an oocyte, gave a maximal increase of 16% at the sameapplied magnetic field and membrane depolarization between -14 mV and -7 mV(see Figure 4). We attribute this resonant behavior to stochastic resonancebetween the thermal activations of the configuration of interacting ions in theI_Ks channel over a low potential barrier inside the closed state of thechannel and the periodic electromotive force induced across the membrane by theperiodic magnetic field. The partial synchronization of the random jumps withthe periodic force changes the relative times spent on either side of thebarrier, thereby changing the open probability of the spontaneously gating openchannel. This, in turn, changes the conductance of the channel at theparticular depolarization level and frequency and is expressed in theHodgkin-Huxley equations as a bump at the given voltage in theconductance-voltage relation. We integrate the modified Hodgkin-Huxleyequations for the current into the Luo-Rudy model of a Guinea pig ventricularcardiac myocyte and obtain increased conductance during the plateau of theaction potential in the cell. This shortens both the action potential and thecytosolic calcium concentration spike durations, lowers its amplitude,increases cytosolic sodium, and lowers cytosolic potassium concentrations. Theshortening of the ventricular calcium signal shortens the QT period of the ECG.

Stochastic resonance of ELF-EMF in voltage-gated channels: the case of the cardiac I_Ks potassium channel