Starzak and Starzak (1978. IEEE Trans. Biomed. Eng. 25:201–204.) proposed that, in cyclic application of current and voltage-clamps, the fidelity of the match of the output current with the original stimulus could be used to measure the spatial uniformity of voltage in a membrane. However, they failed to find such a match in experiments on either squid axons or an electronic model of a membrane patch. Computer simulations of such experiments show that the failure to return the initial pattern may arise from shortcomings of the instruments or instability of membrane characteristics. Logical arguments show that such cyclic experiments are not able to provide information about spatial gradients of membrane voltage.
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