110.

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		2.5.7— Ion Channel Kinetics: Physical Meaning of the Random and Deterministic Models

		1— Random: Driven by Heat

		The physical interpretation of the Markov model is that the ion channel protein is like a small molecule that is relentless kicked by thermal fluctuations from one state to another.

		It conserves energy and it is therefore in local thermodynamic equilibrium with its environment.

		It sits in a state, and sits in a state, until one time, by chance, not based on any physical antecedent, a bit of heat is added from the environment that suddenly provides enough energy for the channel to change its shape from one state to another state.

		2— Deterministic: Little Machines with Sticks and Springs

		The physical interpretation of the iterated map model is that the ion channel protein is large enough to behave partially as a true mechanical system.

		It is a nonlinear, mechanical oscillator composed of sticks and springs. The sticks are called atoms. The springs are called atomic, electrostatic, and hydrophobic forces. This mechanical device organizes nonperiodic thermal fluctuations in its structure into coherent motions. Small motions within the channel protein are amplified by its structure and forces into large, coherent motions that drive the shape of the protein from one state to another.

		It dissipates energy and it is therefore not in local thermodynamic equilibrium with its environment.

		It is like a miniature, mechanical machine. Its sticks and springs perform reproducible, functionally important motions when set into action by the binding of a ligand or a change in the voltage across the cell membrane.

 

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