Simultaneous multicompartment intracellular Ca²⁺ measurements in the perfused heart using ¹⁹F NMR spectroscopy

Although Ca²⁺ transport regulation at subcellular organelles is of great interest, only limited methodology has been available for measuring organellar [Ca²⁺] levels. The present study employs the ¹⁹F NMR resonance frequency of 4F-BAPTA to measure free [Ca²⁺]. In 4F-BAPTA loaded perfused rabbit hearts, two ¹⁹F NMR resonances were clearly observed. The frequency of one was consistent with cytosolic [Ca²⁺] levels. Responses to agents that alter sarcoplasmic reticulum function identified the other resonance as originating from that organelle. The experiments demonstrate the utility of NMR shift indicator methodology in obtaining simultaneous multicompartment intracellular [Ca²⁺] measurements and in enabling organellar [Ca²⁺] measurements to be made from within intact living tissue.