title: Specific inhibition of cardiac and skeletal muscle sarcoplasmic reticulum Ca2+ pumps by H-89.
abstract: The isoquinolinesulfonamide H-89, an inhibitor of cyclic AMP-dependent protein kinases (EC 2.7.1.37, cAPrK), inhibited the Ca2+-ATPase activity of cardiac and skeletal muscle sarcoplasmic reticulum (SR) with concentrations giving half-maximal inhibition of 8.1 +/- 1.3 and 7.2 +/- 0.9 micromol/L, respectively. The effect of H-89 on cardiac SR Ca2+-ATPase (EC 3.6.1.38) was the same irrespective of the presence or absence of inhibitors of cAPrK and furthermore, was not affected by a neutralising monoclonal antibody raised against phospholamban. Thus, the action of H-89 in inhibiting SR Ca2+-ATPase would not appear to be mediated by inhibition of cAPrK to reduce the phosphorylation state of phospholamban. In both cardiac and skeletal muscle SR, the inhibition by H-89 was noncompetitive with respect to ATP at a low concentration of ATP (<1 mmol/L) and of a mixed pattern at high concentrations of ATP. H-89 produced a decrease in affinity of the SR Ca2+ pump to Ca2+ with an increase in the Km for Ca from 0.52 +/- 0.01 to 0.94 +/- 0.03 micromol/L (P < 0.05) in cardiac SR and from 0.39 +/- 0.01 to 0.79 +/- 0.02 micromol/L (P < 0.05) in skeletal muscle SR. These results suggest that H-89 inhibits SR Ca2+-ATPase by a direct action on the SR Ca2+ pump to decrease its affinity to Ca2+. Such an action may contribute to the pharmacological effect of H-89.
authors.affiliation: SmithKline Beecham Laboratoires Pharmaceutiques, Sainte-Grégoire, France.
authors.forename: P
authors.initials: P
authors.lastname: Lahouratate
authors.forename: J
authors.initials: J
authors.lastname: Guibert
authors.forename: J C
authors.initials: JC
authors.lastname: Camelin
authors.forename: I
authors.initials: I
authors.lastname: Bertrand
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002135:Calcium-Binding Proteins / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007546:Isoquinolines / Q000494:pharmacology*; D018482:Muscle, Skeletal / Q000201:enzymology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013449:Sulfonamides; D000099211:Phospholamban
chemical_list: D000255:Adenosine Triphosphate; D000911:Antibodies, Monoclonal; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D017868:Cyclic AMP-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D013449:Sulfonamides; D000099211:Phospholamban; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide