title: Neutral carrier-based "Ca(2+)-selective" microelectrodes for the measurement of tetraphenylphosphonium.
abstract: 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.
authors.affiliation: Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: V K
authors.initials: VK
authors.lastname: Mootha
authors.forename: S
authors.initials: S
authors.lastname: French
authors.forename: R S
authors.initials: RS
authors.lastname: Balaban
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis*; D003959:Diamines; D008297:Male; D008564:Membrane Potentials; D008839:Microelectrodes; D015335:Molecular Probes; D009861:Onium Compounds / Q000032:analysis*; D009943:Organophosphorus Compounds / Q000032:analysis*; D010101:Oxygen Consumption / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity
chemical_list: D003959:Diamines; D015335:Molecular Probes; D009861:Onium Compounds; D009943:Organophosphorus Compounds; C045768:ETH 1001; D002118:Calcium; C013289:tetraphenylphosphonium