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| - Pore Formation by 6-Ketocholestanol in PhospholipidMonolayers and Its Interpretation by a GeneralNucleation-and-Growth Model Accounting for the SigmoidalShape of Voltage-Clamp Curves of Ion Channels
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| - 6-Ketocholestanol (KC), a steroid that differs from cholesterol mainly by the presence of a carbonylgroup, forms pores inside a dioleoylphosphatidylcholine monolayer self-assembled on mercury by amechanism similar to that of channel-forming peptides and proteins. The potential steps responsible forpore formation by KC molecules give rise to potentiostatic charge vs time curves whose sigmoidal shapeand potential dependence can be quantitatively interpreted on the basis of a mechanism of nucleation andgrowth of KC clusters. Pore formation by KC allows the penetration of thallous ions across the otherwiseimpermeable phosphatidylcholine monolayer, while pore disruption taking place at more negative potentialscauses a drop in thallous ion permeation. Pore disruption is also accounted for by a mechanism of nucleationand growth of holes inside the KC clusters. The kinetic model of nucleation and growth is general, andaccounts quantitatively for the sigmoidal shape and potential dependence of the classical Hodgkin-Huxleyvoltage-clamp curves of potassium channels in squid giant axon, using a minimum number of freeparameters.
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