Characterisation of neurotransmitter-induced electrolyte transport in cockroach salivary glands by intracellular Ca2+, Na+ and pH measurements in duct cells.
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 pHi) 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 pHi and increases in [Na+]i and [Ca2+]i in duct cells; (2) in contrast, DA stimulation of isolated ducts produces only a small pHi drop and no changes in [Na+]i and [Ca2+]i; (3) pHi 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 pHi 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 pHi changes in duct cells; we consider that these transporters are involved in the secretion of the NaCl-rich primary saliva.
Hille
Carsten
C
University of Potsdam, Institute of Biochemistry and Biology, Department of Animal Physiology, 14476 Potsdam-Golm, Germany. hille@uni-potsdam.de
Walz
Bernd
B
D000251:Adenosine Triphosphatases / Q000737:chemistry; D000818:Animals; D027321:Anion Transport Proteins / Q000737:chemistry; D001692:Biological Transport / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide / Q000737:chemistry; D003058:Cockroaches / Q000378:metabolism*; D004573:Electrolytes / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D018377:Neurotransmitter Agents / Q000378:metabolism*; D012469:Salivary Glands / Q000166:cytology / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000737:chemistry; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism
D027321:Anion Transport Proteins; D004573:Electrolytes; D018377:Neurotransmitter Agents; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D002245:Carbon Dioxide; D012965:Sodium Chloride; D012964:Sodium; D000251:Adenosine Triphosphatases; C031652:anion-sensitive ATPases; D002118:Calcium