Fig. 6. Spontaneous oscillations of the basolateral membrane voltage (V_bl) in an isolated Malpighian tubule of Aedes aegypti. Three principal cells were impaled with conventional microelectrodes. The remaining epithelial cells (more than 120) are not shown in the tubule diagram. Note that cell 2 separates cell 1 (red trace) from cells 3 (blue trace) and 4 (green trace) from which voltages are recorded.