Dopamine stimulates salivary duct cells in the cockroach Periplaneta americana

This study examines whether the salivary duct cells of the cockroach Peripl aneta americana can be stimulated by the neurotransmitters dopamine and ser otonin, We have carried out digital Ca2+-imaging experiments using the Ca2-sensitive dye fura-2 and conventional intracellular recordings from isolat ed salivary glands. Dopamine evokes a slow, almost tonic, and reversible do se-dependent elevation in [Ca2+](i) in the duct cells. Upon stimulation wit h 10(-6) mol l(-1) dopamine, [Ca2+](i) rises from 48+/-4 nmol l(-1) to 311/-43 nmol l(-1) (mean +/- S.E.M., N=18) within 200-300s. The dopamine-induc ed elevation in [Ca2+](i) is absent in Ca2+-free saline and is blocked by 1 0(-4)mol l(-1) La3+, indicating that dopamine induces an influx of Ca2+ acr oss the basolateral membrane of the duct cells. Stimulation with 10(-6)mol l(-1) dopamine causes the basolateral membrane to depolarize from -67+/-1 t o -41+2/- mV (N=10), This depolarization is also blocked by La3+ and is abo lished when Na+ in the bath solution is reduced to 10mmol l(-1). Serotonin affects neither [Ca2+](i) nor the basolateral membrane potential of the duc t cells. These data indicate that the neurotransmitter dopamine, which has previously been shown to stimulate fluid secretion from the glands, also st imulates the salivary duct cells. suggesting that dopamine controls their m ost probable function, the modification of primary saliva.