POWRE: Analysis of Space-clamp Errors in Voltage-clamp Experiments on an Extended Neuron

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The goal of this research project is to better understand a serious type of error that can arise when an important measurement procedure (the "voltage clamp") is used in experimental neurophysiology and biophysics. Voltage-clamp methods are widely used to characterize quantitatively properties of ionic channels in neurons. An intrinsic defect in the procedure gives rise to what are termed "space-clamp errors" when the voltage clamp is applied to certain cells. In order for the voltage clamp to yield an accurate measurement of ionic conductance across a cell membrane, the current must be measured across a patch of membrane with no spatial variation in the voltage. However, in many research applications there is no practical way of achieving spatial uniformity of potential. In neurophysiology, for example, axons and dendrites attached to a nerve-cell body (i.e., long or "extended" neurons) are a common source of spatial voltage variation. It is sometimes possible to modify the experimental procedure in order to reduce space-clamp errors; however, the results are not always satisfactory, and the scope of such modification is limited. An alternative is post-experimental analysis and correction based on mathematical models and computer simulation. This project will carry out such an analysis. In particular: (1) computer simulations will be carried out for space-clamp errors arising from voltage clamp of a simplified model of an extended neuron; and (2) mathematical models of a neuron with active ionic channels will be developed based on modifications of the "cable equations," which were originally developed for membranes with no active channels. The results of the simulations, and the fitted mathematical models, will then be subjected to analysis in order that the nature and magnitude of space-clamp errors can be assessed, and that criteria for recognition of, and correction for, these errors can be developed.This POWRE project will enable Dr. Castelfranco to return to a research program in mathematical neurophysiology consistent with her training and scientific interests, following an involuntary hiatus of several years. Moreover, it will transform her official status within her home institution to one that will increase her access to resources and raise the visibility of her research.