Fig. 5. Mechanisms of action of leucokinin. Leucokinin belongs to the kinin family of insect diuretic peptides. Leucokinin increases the rates of both transepithelial NaCl and KCl secretion by increasing the paracellular Cl^- conductance via intra- and extracellular Ca²⁺. Septate junctional proteins (claudins, neurexins) are hypothesized to form channel-like extracellular structures with permselectivity and variable conductance (Beyenbach, 2003). Table 3 documents the non-selective stimulation of transepithelial NaCl and KCl secretion. G, heterotrimeric G-protein; PLC, phospholipase C; IP₃, inositol (1,4,5)-trisphosphate. Data from Yu and Beyenbach, 2002.