Mechanism For BKs And BKi Channels Regulating Action Potential In Rat Chromaffin Cells

BK channel is a kind of large conductance calcium and voltage activated potassium channel that is found in all excitable and unexcitable channels except heart myocytes. It plays the key role in physiological process, such as regulating the membrane potential. However, traditional Hodgkin-Huxley ( H-H ) model can not describe its kinetic features very well because of the complexity of its kinetic mechanism. So, we can't use H-H theory to find out its function during action potential (AP) firing. In our studying, we use the MWC allosteric kinetic method to set up a BK model, instead of using the simple H-H-like expressions. And then, we use this model to simulate the BK channel's contribution during AP in rat chromaffin cells (RCC) .In the thesis, we take BK channel as the research object, and analysis the experiment data thoroughly, and clearly demonstrate the channel activation, deactivation, inactivation and recovery process. Based on these analyses, we build up the BK channel's allosteric model, and give a series of methods to get the model parameters.During analyzing the tail current traces of BKi inactivation, we deduce the traditional conductance calculation method and adjusted the ion channel conductance expression in H-H model according with the current rectifying.Based on inducing the protein allosteric model theory, we got some further knowledge about the channel states transition, from both biophysical and chemical kinetics view. We consider the model's states transition as a Markov process, and set up a series of ordinary differential equations to describe these process.For this, we develop a simulation program named CeL in the past several years. With the Runge-Kutta algorithm, this program gives time-based integral solutions of ordinary differential equations according with the channel states, and finally simulates the ion channels' currents.According to the relationship among total transmembrane current, membrane capacitance and membrane potential, we composed different channel models as a cell model and succeed simulating the action potential.Based on the data from simulation and experiments, we have proved that BK channel can modify the repolarization, hyper-polarization and after-hyper-polarization of action potential (AP) , and the inactivating BK channel (BKi) can accelerate the repetitive firing of AP while the non-inactivating BK channel (BKs) can stop it. Meanwhile, we have found during the firing period, the BKi currents recover to a stable level after a rise, by contract, the BKs currents have an infinite rise. As well as, there is only one AP firing when Ca²⁺ is removed from extracellular saline. We found that the key aspect of BK channels that supports repetitive firing in these cells is not the beta2 subunit induced inactivation of BK channels, but the more negatively shifted range of activation produced by the beta2 subunit.Due to its easily-acquiring and flexibility, the new method would be more exactitude and convenience as a probe for ion channels, and even has a widly application in research on cell excretion.