title: Interference of calmidazolium with measurement of mitochondrial membrane potential using the tetraphenylphosphonium electrode or the fluorescent probe rhodamine 123.
abstract: Calmidazolium (CMZ) is a positively charged, hydrophobic compound used as a calmodulin antagonist. It may cause unspecific effects in mitochondria, e.g., a decrease in membrane potential (deltapsi), swelling, and uncoupling. Several groups have advised against use of CMZ in studying signal transduction in mitochondria. We report here that it interferes with measurement of deltapsi in rat liver mitochondria (RLM) when using the tetraphenyl phosphonium (TPP+) electrode. We also found that CMZ reduces the signal, indicating an apparent drop in deltapsi. CMZ itself gave a signal with the TPP+ electrode in the absence of RLM. At high concentrations, > 10 microM, it also reduced the fluorescence quenching of the probe rhodamine 123. This may be due to an interference with mitochondrial uptake and binding of this positively charged probe or to an uncoupling effect. It is concluded that CMZ and similar positively charged calmodulin antagonists such as trifluoperazine may be used in mitochondria if these interferences are controlled and calibration is carried out under the experimental conditions used.
authors.affiliation: Department of Applied Chemistry and Microbiology, Viikki Biocenter I, P.O.Box 56, University of Helsinki, FIN-00014 Helsinki, Finland. nils-erik.saris@helsinki.fi
authors.forename: Nils-Erik L
authors.initials: NE
authors.lastname: Saris
authors.forename: Vera V
authors.initials: VV
authors.lastname: Teplova
authors.forename: Irina V
authors.initials: IV
authors.lastname: Odinokova
authors.forename: Tamara S
authors.initials: TS
authors.lastname: Azarashvily
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002138:Calibration; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry / Q000379:methods*; D004566:Electrodes; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D007093:Imidazoles / Q000378:metabolism / Q000494:pharmacology*; D007202:Indicators and Reagents; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000502:physiology; D009861:Onium Compounds / Q000737:chemistry / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D020112:Rhodamine 123; D015398:Signal Transduction / Q000502:physiology; D013997:Time Factors; D014268:Trifluoperazine / Q000737:chemistry / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007093:Imidazoles; D007202:Indicators and Reagents; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D020112:Rhodamine 123; D014268:Trifluoperazine; C031938:calmidazolium; D002118:Calcium; C013289:tetraphenylphosphonium