A Synthetic Fluorescent Mitochondria-Targeted Sensor for Ratiometric Imaging of Calcium in Live Cells

Ca2+handlingby mitochondria is crucialfor cell lifeand the directmeasureof mitochondrialCa2+concentrationinlivingcellsis of pivotalinterest.Genetically-encodedindicatorsgreatlyfacilitatedthis task,howevertheyrequiredemandingdeliveryprocedures.Onthe otherhand,existingmitochondria-targetedsyntheticCa2+indicatorsare plaguedby severaldrawbacks,for example,non-specificlocalization,leakage,toxicity.Here we reportthe synthesisand characterizationofanew fluorescentCa2+sensor,namedmt-fura-2,obtainedbycouplingtwo triphenylphosphoniumcationsto the molecularbackboneof the ratiometricCa2+indicatorfura-2.Mt-fura-2bindsCa2+withadissociationconstantof1.5mmin vitro.Whenloadedin differentcell typesas acetoxymethylester,theprobeshowspropermitochondriallocalizationand accuratelymeasuresmatrix[Ca2+]variations,provingits superiorityoveravailabledyes.Wedescribethe synthesis,characterizationandapplicationof mt-fura-2to cell typeswherethe deliveryofgenetically-encodedindicatorsis troublesome.