Fluorescence signals in ANS-stained squid giant axons during voltage-clamp

SummaryAn analysis is presented of the changes in fluorescence intensity, associated with nerve stimulation, of 1-anilinonaphthalene-8-sulfonate (ANS) injected in squid axons. A preliminary and qualitative account of the physiological modifications produced by the ANS injection is also given. The time course of the fluorescence intensity during the first 300 μsec following the onset of voltage-clamp is shown to be exponential with a time constant of about 35 ηmsec, fairly independent of the amplitude and sign of the applied voltage, the intensity increasing during hyperpolarizations and decreasing during depolarizations. Data are presented on the relationship between the amplitude of the changes in fluorescence intensity and the voltage applied, the amplitude of the changes associated with depolarizations being measured at the time of occurence of the peak inward current. The interpretation of the changes in fluorescence intensity in terms of electrophoretic effects or as being due to a direct effect of the electric field upon the quantum yield of ANS fluorescence, is hardly compatible with the results of our present analysis.

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