Saliva secretion and ionic composition of saliva in the cockroach Periplaneta americana after serotonin and dopamine stimulation, and effects of ouabain and bumetamide

Isolated salivary glands of Periplaneta americana were used to measure secretion rates and, by quantitative capillary electrophoresis, Na+, K+, and Cl− concentrations in saliva collected during dopamine (1 μM) and serotonin (1 μM) stimulation in the absence and presence of ouabain (100 μM) or bumetanide (10 μM). Dopamine stimulated secretion of a NaCl-rich hyposmotic saliva containing (mM): Na+ 95 ± 2; K+ 38 ± 1; Cl- 145 ± 3. Saliva collected during serotonin stimulation had a similar composition. Bumetanide decreased secretion rates induced by dopamine and serotonin; secreted saliva had lower Na+, K+ and Cl− concentrations and osmolarity. Ouabain caused increased secretion rates on a serotonin background. Saliva secreted during dopamine but not serotonin stimulation in the presence of ouabain had lower K+ and higher Na+ and Cl− concentrations, and was isosmotic. We concluded: The Na+-K+-2Cl− cotransporter is of cardinal importance for electrolyte and fluid secretion. The Na+/K+-ATPase contributes to apical Na+ outward transport and Na+ and K+ cycling across the basolateral membrane in acinar P-cells. The salivary ducts modify the primary saliva by Na+ reabsorption and K+ secretion, whereby Na+ reabsorption is energized by the basolateral Na+/K+-ATPase which imports also some of the K+ needed for apical K+ extrusion.