title: Dopamine-induced graded intracellular Ca2+ elevation via the Na+Ca2+ exchanger operating in the Ca2+-entry mode in cockroach salivary ducts.
abstract: Stimulation with the neurotransmitter dopamine causes an amplitude-modulated increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) in epithelial cells of the ducts of cockroach salivary glands. This is completely attributable to a Ca(2+) influx from the extracellular space. Additionally, dopamine induces a massive [Na(+)](i) elevation via the Na(+)K(+)2Cl(-) cotransporter (NKCC). We have reasoned that Ca(2+)-entry is mediated by the Na(+)Ca(2+) exchanger (NCE) operating in the Ca(2+)-entry mode. To test this hypothesis, [Ca(2+)](i) and [Na(+)](i) were measured by using the fluorescent dyes Fura-2, Fluo-3, and SBFI. Inhibition of Na(+)-entry from the extracellular space by removal of extracellular Na(+) or inhibition of the NKCC by 10 microM bumetanide did not influence resting [Ca(2+)](i) but completely abolished the dopamine-induced [Ca(2+)](i) elevation. Simultaneous recordings of [Ca(2+)](i) and [Na(+)](i) revealed that the dopamine-induced [Na(+)](i) elevation preceded the [Ca(2+)](i) elevation. During dopamine stimulation, the generation of an outward Na(+) concentration gradient by removal of extracellular Na(+) boosted the [Ca(2+)](i) elevation. Furthermore, prolonging the dopamine-induced [Na(+)](i) rise by blocking the Na(+)/K(+)-ATPase reduced the recovery from [Ca(2+)](i) elevation. These results indicate that dopamine induces a massive NKCC-mediated elevation in [Na(+)](i), which reverses the NCE activity into the reverse mode causing a graded [Ca(2+)](i) elevation in the duct cells.
authors.affiliation: Institute of Biochemistry and Biology, Department of Animal Physiology, University of Potsdam, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Hille
authors.forename: Bernd
authors.initials: B
authors.lastname: Walz
mesh_terms: D000818:Animals; D002034:Bumetanide / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D003058:Cockroaches; D004298:Dopamine / Q000494:pharmacology*; D005456:Fluorescent Dyes / Q000032:analysis; D016257:Fura-2 / Q000032:analysis; D066298:In Vitro Techniques; D010042:Ouabain / Q000494:pharmacology; D018987:Salivary Ducts / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000502:physiology*
chemical_list: D005456:Fluorescent Dyes; D019831:Sodium-Calcium Exchanger; D002034:Bumetanide; D010042:Ouabain; D012964:Sodium; D002118:Calcium; D016257:Fura-2; D004298:Dopamine