title: A calmodulin antagonist inhibits histamine-stimulated acid production by isolated rat parietal cells.
abstract: The role of calmodulin in the regulation of histamine-stimulated parietal cell function was studied in isolated rat parietal cells using [14C]aminopyrine uptake as a quantitative index of acid production. In enriched (77-87%) intact parietal cells the calmodulin antagonist naphthalene sulfonamide W 7 dose-dependently inhibited the response to 10(-4) M histamine (IC50: 2 X 10(-6) M). The mechanism of this inhibition was examined further with two other stimuli of H+-production: forskolin which directly activates the parietal cell adenylate cyclase without interacting at the histamine H2-receptor and dbcAMP which mimics the biological action of cAMP without preceding activation of adenylate cyclase. W 7 effectively inhibited the responses to 10(-4) M forskolin (IC50: 6 X 10(-7) M), 10(-3) M dbcAMP (IC50: 10(-6) M) and to 10(-2) M K+ (IC50: 3 X 10(-6) M). The action of W 7 followed non-competitive kinetics since the antagonist reduced the entire range of the concentration-response curves without shifting them rightwards towards higher concentrations of the respective stimulants. The effect of W 7 was reversed by washing the cells. ATP-induced [14C]aminopyrine uptake into digitonin-permeabilized oligomycin-inhibited parietal cells reflects H+-production independent of oxidative phosphorylation and was also inhibited by W 7 (IC50: 10(-5) M). Inhibition of K+-stimulated H+/K+-ATPase activity required even higher W 7-concentrations (IC50: 1.4 X 10(-4) M). Our data suggest that calmodulin might be involved in the intracellular mediation of the response to histamine. Between histamine-induced cAMP-generation and the H+-secreting tubulovesicular system W 7 seems to inhibit an intracellular step that finally activates the H+/K+-ATPase. Yet, direct inhibition of the ATPase requires W 7 concentrations of questionable specificity and is unlikely to be the mechanism behind the action of W 7 on the parietal cell response to histamine.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000632:Aminopyrine / Q000378:metabolism; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D005576:Colforsin / Q000494:pharmacology; D005744:Gastric Acid / Q000378:metabolism*; D017506:H(+)-K(+)-Exchanging ATPase; D006632:Histamine / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D009840:Oligomycins / Q000494:pharmacology; D010295:Parietal Cells, Gastric / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011970:Receptors, Histamine H2 / Q000502:physiology; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D009840:Oligomycins; D011970:Receptors, Histamine H2; D013449:Sulfonamides; D000632:Aminopyrine; D005576:Colforsin; D003994:Bucladesine; C017967:W 7; D006632:Histamine; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium