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Anal Biochem. 1996 May 1;236(2):327-30.

Neutral carrier-based "Ca(2+)-selective" microelectrodes for the measurement of tetraphenylphosphonium.

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Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.


Ca(2+)-selective microelectrodes with Simon's neutral carrier ETH 1001 are commercially available and have been widely used for the measurement of both extra- and intracellular calcium. The electrodes demonstrate high selectivity against other cations such as magnesium, sodium, and potassium. We report, however, that the ETH 1001-based microelectrode is a superior tetraphenylphosphonium (TPP+)-sensitive electrode. The electrode exhibits a Nernstian response for [Ca2+] > 10(-5) M but for [TTP+] > 10(-7) M. Using two different methods, we found that log kTTPCa (selectivity coefficient for TPP+ with respect to Ca2+) is in the range of -3.0 to -5.3. We argue that the ETH 1001 microelectrode can be used as a commercially available TPP+ electrode. We illustrate this application by making membrane potential recordings in respiring mitochondria. The results are identical to those obtained using conventional ion-exchange TPP+ electrodes.

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