Ion Channel Markov Modeling And Analysis

Electrical behaviors in live cells, which based on the Physical activity of ion channels,are one of essential characters of life. Many important physiological processes arecorrelate with ion channel, such as cell excitability, cell volume, stable intracellularenvironment, the generation and conduction of nerve signals, cell division, reproductivedevelopment, muscle movement, hormone and neurotransmitter secretion, etc. Thereforeboth in theory and practice, it’s greatly significant to find the mechanism of ion channel incell activities.BK（Large-conductance calcium-activated potassium） channel is one type of ionchannels, which is widely expressed in excitable and non-excitable cells, and functions inmany important physiological process, such as: the formation of action potential andmuscle movement, etc. Its calcium sensitivity and β1subunit is critical to the transmit ofneural signal and vascular tone, with a high research value and significance.In the methods of ion channel working mechanism study, ion channel Markov modelis a mathematical model which can reflect dynamic relationship of transitions between thestates of channel in specific physiological and environmental conditions. The significanceof building the Markov model is to characterize the working mechanism of the ionchannel quantitatively, to explain the structure and physiological function of ion channelprotein and to reveal the pathogenic mechanism of ion channel-related diseases. However,during Markov modeling process, there are several difficulties: too complex modelstructure, too many model parameters, too many data used in modeling and so on, whichcan not be easily solved by traditional methods. Except Markov modeling, in BK calciumsensitivity measurement and β1subunit function analysis, complex inverse problemsolving is involved, which can not be solved by existed method.Evolutionary computation, which based on natural evolution, specializes in solvingglobal optimization problems with the probabilistic search technology. Its search processdoes not depend on the initial value, gradient information or other auxiliary knowledge.It’s adptive for the kind of issue, therefore it’s usful in ion channel modeling and inverseproblem solving. In this dissertation, electrophysiological techniques combined with computersimulation method are used. First, we built Markov models for many ion channels usingevolutionary computation method. Then the calcium sensitivity and β1functions in BKchannels are analyzed quantitatively:First, a software CeL was developed, based on an evolutionary computation methodwe designed, PSO-GSS. To make the modeling process more efficient and faster, weproposed a method of estimating the initial values of the model parameters frommacroscopic currents, which can be applied in parameters optimization of each model, anda better result can be gotten. Compare with the software with similar functions,CeL wasmuch better in the modeling performance and have reached the international advancedlevel. Additionally, using CeL, we analyzed a mass of electrophysiological data fromexperiments and built many Markov models of different channels: BK, KV, Ca, NaVandso on.Second, by means of laser flash photolysis techniques, several unusual properties ofBK currents were found: biphasic activation and voltage-dependent constant Rf. Using ESand BK flash current as a sensor, we accurately calculated the intracellular local calciumconcentration change process firstly in the world. Additionally, a method was proposed toestimate the binding rate constant of [Ca²⁺] in the article and the [Ca²⁺] binding rateconstant of four BK mutant were determined. Considering Ca²⁺’s function of secondmessenger in BK channel, this work was greatly significant for the study of themechanism of generation and conduction of nerve signals.Finally, BK（mSloα） and BK（mSloα+β1） currents were analyzed, and using which therelative50-states BK models were built. The built model was the first one in the world.Using the built50-states BK model, we successfully built the SM cell model and simulatetheir action potential. This study concluded that β1subunit enhanced hyperpolarization ofcells and reduced intracellular calcium concentration, which lead to the relaxation ofarteries. The work had laid a basis for underlying the vasoregulation mechanism.Additionally, because the changes in intracellular Ca²⁺were consistent to the changes indiameters of arteries, the β1subunit gene should be a candidate genetic locus for humanhypertension. In summary, our study demonstrates the the calcium sensitivities and the function ofβ1subunit in BK channels and their mutants, which can be future used in the mechanismresearch of vasoregulation and nerve activities. Meanwhile, as an innovation research way,CeL and its derivative methods expand the technique of biophysical study and greatlyimproves the efficiency of researches.