Ion and water transport by isolated cockroach salivary glands

Summary When the isolated salivary glands of the cockroachNauphoeta cinerea Olivier are stimulated by dopamine, the putative neurotransmitter, they secrete a fluid containing (mm): Na, 121; K, 47; Cl, 143. Stimulation of glands by 5-hydroxytryptamine or the neurotransmitter evokes a secretion identical in Na composition to this. Dopamine-evoked secretion is abolished in the absence of extracellular Na. The relationship between the rates of fluid secretion and Na transport is linear. However, at very low rates of secretion the Na concentration falls. Calcium, K and Cl ions can be removed from the bathing solution without abolishing fluid secretion. Our evidence suggests that (i) the primary secretion is formed by active transport of Na in the acini, and (ii) the ionic composition of this secretion is modified by re-absorption of Na and an independent secretion of K in the ducts.