A vacuolar-type H+-ATPase and a Na+/H+ exchanger contribute to intracellular pH regulation in cockroach salivary ducts.
Cells of the dopaminergically innervated salivary ducts in the cockroach Periplaneta americana have a vacuolar-type H(+)-ATPase (V-ATPase) of unknown function in their apical membrane. We have studied whether dopamine affects intracellular pH (pH(i)) in duct cells and whether and to what extent the apical V-ATPase contributes to pH(i) regulation. pH(i) measurements with double-barrelled pH-sensitive microelectrodes and the fluorescent dye BCECF have revealed: (1) the steady-state pH(i) is 7.3+/-0.1; (2) dopamine induces a dose-dependent acidification up to pH 6.9+/-0.1 at 1 micromol l(-1) dopamine, EC(50) at 30 nmol l(-1) dopamine; (3) V-ATPase inhibition with concanamycin A or Na(+)-free physiological saline (PS) does not affect the steady-state pH(i); (4) concanamycin A, Na(+) -free PS and Na(+)/H(+) exchange inhibition with 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) each reduce the rate of pH(i) recovery from a dopamine-induced acidification or an acidification induced by an NH(4)Cl pulse; (5) pH(i) recovery after NH(4)Cl-induced acidification is almost completely blocked by concanamycin A in Na(+)-free PS or by concanamycin A applied together with EIPA; (6) pH(i) recovery after dopamine-induced acidification is also completely blocked by concanamycin A in Na(+)-free PS but only partially blocked by concanamycin A applied together with EIPA. We therefore conclude that the apical V-ATPase and a basolateral Na(+)/H(+) exchange play a minor role in steady-state pH(i) regulation but contribute both to H(+) extrusion after an acute dopamine- or NH(4)Cl-induced acid load.
Hille
Carsten
C
University of Potsdam, Institute of Biochemistry and Biology, Department of Animal Physiology, Karl-Liebknecht-Strasse 24-25, 14476 Potsdam-Golm, Germany.
Walz
Bernd
B
D000136:Acid-Base Equilibrium / Q000187:drug effects*; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000643:Ammonium Chloride; D000704:Analysis of Variance; D000818:Animals; D003592:Cytophotometry; D004298:Dopamine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000737:chemistry*; D018942:Macrolides / Q000494:pharmacology; D008839:Microelectrodes; D010526:Periplaneta / Q000201:enzymology*; D018987:Salivary Ducts / Q000201:enzymology*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D018942:Macrolides; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; D000584:Amiloride; C036978:concanamycin A; D025262:Vacuolar Proton-Translocating ATPases; D004298:Dopamine; C039614:ethylisopropylamiloride