A plug-in minielectrode for measurements in stirred photometric cuvettes

A device is described to perform potentiometric measurements with ion-sensitive electrodes in stirred photometric cuvettes. Its design allows to make additions to the reaction medium with microliter syringes during measurements. Originally, this plug-in electrode was designed to register the free Ca2+ concentrations in the incubation medium of mitochondrial suspensions during measurements of the free matrix Ca2+ concentration with a permeant fluorescent Ca2+ indicator. However, numerous other applications can be easily realized, such as the combination of mitochondrial light-scattering measurements and ion-transport measurements, the combination of the permeabilized cell technique with fluorescence measurements of intracellular organelles or simply the calibration of the fluorescence of Ca2+ indicators with a Ca2+ ion-sensitive minielectrode. Compared with the use of a second fluorescent indicator the use of an electrode has the advantage that the signal can be transformed into ion concentrations already during the measurements.