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Combined recordings of membrane potential and calcium currents

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In a typical ‘voltage-clamp’ experiment, membrane channels are studied by artificial rapid steps of voltage and the resulting transmembrane current is thus unnatural. This is a clear limitation in studying the physiological function of native calcium channels.

In a recent issue of The Journal of Physiology, two researchers of the LIPhy offer a solution to this technical limitation for calcium channels . They record membrane potential waveform with voltage-sensitive dye and calcium current waveform with a calcium-sensitive dye. To extract the waveform of the dendritic voltage-gated calcium current, Jaafari and Canepari combine three strategies : (i) low affinity calcium indicator dye OGB5N (Kd = 20 μM), (ii) fast optical recording at 20 kHz frame rate, and (iii) mathematical transformation (derivative of the fluorescence change). The resulting optical waveforms match the calcium current waveforms (Jaafari et al. 2014). In the near future we expect this type of optical measurement to be applied to thin dendritic branches of many neuronal types across the central nervous system. This will remarkably impact of knowledge on the physiology of calcium channels.