8 - X-Ray Microprobe Analysis of Voltage-Clamped Single Heart Ventricular Myocytes

Publisher Summary This chapter presents X-ray microprobe analysis of voltage-clamped single heart ventricular myocytes. Voltage-clamp experiments, when performed with patch electrodes, are thought to go along with cell-dialysis—that is, the electrolytes filling the patch electrode are expected to diffuse into the myoplasm. In such a way, it is possible to modify the myoplasmic [Na + ] and, thereby, the Ca 2+ influx through the Na + /Ca 2+ exchanger. This chapter describes a method that allows electron probe microanalysis (EPMA) of voltage-clamped single heart ventricular cells. The chapter presents two examples that illustrate the usefulness of this method. The first example deals with Ca-depleted myocytes. Reloading with Ca is done with five Ca 2+ currents. The effects of Ca 2+ influx on the concentration is monitored by Indo-1 fluorescence. EPMA applied at the moment of defined global cellular Ca load provides the information about how much of this Ca is bound or stored in compartments. The second example applies EPMA to myocytes that were voltage clamped with paired pulses to bring their cellular Ca load to a high steady state.