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First published online February 1, 2008
Journal of Experimental Biology 211, 568-576 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.010207

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Characterisation of neurotransmitter-induced electrolyte transport in cockroach salivary glands by intracellular Ca²⁺, Na⁺ and pH measurements in duct cells

Carsten Hille^* and Bernd Walz

University of Potsdam, Institute of Biochemistry and Biology, Department of Animal Physiology, 14476 Potsdam-Golm, Germany

^* Author for correspondence at present address: University of Potsdam, Institute of Chemistry, Department of Physical Chemistry, 14476 Potsdam-Golm, Germany (e-mail: hille{at}uni-potsdam.de)

Accepted 10 December 2007

Ion-transporting acinar peripheral cells in cockroach salivary glands are innervated by dopaminergic and serotonergic fibres, but saliva-modifying duct cells are innervated only by dopaminergic fibres. We used microfluorometry to record intracellular Na⁺, Ca²⁺ and H⁺ concentrations ([Na⁺]_i, [Ca²⁺]_i and pH_i) in duct cells of two types of preparation, viz `lobes' consisting of acini with their duct system and `isolated ducts' without acini, in order to obtain information about the transporters involved in saliva secretion and/or modification. Our results indicate that (1) stimulation of lobes by dopamine (DA) causes a strong drop of pH_i and increases in [Na⁺]_i and [Ca²⁺]_i in duct cells; (2) in contrast, DA stimulation of isolated ducts produces only a small pH_i drop and no changes in [Na⁺]_i and [Ca²⁺]_i; (3) pH_i and [Ca²⁺]_i changes are also induced in duct cells by serotonin (5-HT) stimulation of lobes, but not isolated ducts; (4) in the absence of CO₂/HCO₃^–, the DA-induced pH_i drop is strongly reduced by removal of extracellular Cl^– or inhibition of the Na⁺–K⁺–2Cl^– cotransporter (NKCC); (5) in the presence of CO₂/HCO₃^–, the DA-induced pH_i drop is not reduced by NKCC inhibition, but rather by inhibition of the Cl^–/HCO₃^– exchanger (AE), Na⁺/H⁺ exchanger (NHE) or carbonic anhydrase. We suggest that DA and 5-HT act predominantly on acinar peripheral cells. Their activity (secretion of primary saliva) seems to cause changes in ion concentrations in duct cells. NKCC and/or AE/NHE activities are necessary for pH_i changes in duct cells; we consider that these transporters are involved in the secretion of the NaCl-rich primary saliva.

Key words: dopamine, serotonin, insect, salivary glands, ion transport, intracellular pH, sodium–potassium–chloride cotransporter, sodium–proton exchanger, anion exchanger