OpdK protein is an 8 A-wide diameter, kidney shaped pore located in the outer membrane of the Gram-negative bacteria. We reconstituted this protein into the planar lipid bilayers and measured the single-channel ionic current. We observed that the OpdK protein pore undergoes a three-state, discrete kinetics, whose current sub-states feature different probabilities of occupancy, rate constants and conductances. We have developed a simple kinetic model to account for the dynamics of spontaneous gating in the OpdK protein pore. Here, we discuss the nature of the gating dynamics of these three current sub-states, which is dependent on the concentration of the KCl in the chamber and applied transmembrane voltage. We propose that these well-defined current sub-states are due to fluctuations of short and long extracellular loops located near to the pore constriction.Acknowledgments: This work was supported by the US NSF grants (DMR-0706517 and DMR-1006332) and by the NIH grants (R01 GM088403 and R01 GM085785).