Dynamic regulation of intracellular potassium is a key feature of astrocytes, as it will determine their capability to regulate extracellular potassium homeostasis during physiology and pathology. However, the study of intracellular potassium dynamics is hindered by the lack of adequate techniques. This chapter outlines a method for calculating astrocytic potassium concentration using the Goldman–Hodgkin–Katz equation. The method integrates experimental measurements of astroglial sodium concentration and membrane potential, along with extracellular potassium and sodium concentrations. We will show how this empirical-theoretical method reveals an initial loss of intracellular potassium and a subsequent transient potassium overshoot upon a protocol that mimics metabolic ischemic stress in acute brain slices.