Mechanism of action of sarcoplasmic reticulum calcium-uptake activators--discrimination between sarco(endo)plasmic reticulum Ca2+ ATPase and phospholamban interaction.
The Ca2+ uptake by the sarcoplasmic reticulum (SR) can be affected by direct modulation of the Ca2+ pump or by removing the inhibitory effect of dephosphorylated phospholamban. The effect of these mechanisms was assessed using ellagic acid and 1-(3,4-dimethoxyphenyl)-3-dodecanone. Both compounds (30 micromol/l) enhanced SR-Ca2+ uptake in rabbit cardiomyocytes by 65.3 +/- 13% and 44.3 +/- 6.7% for 1-(3,4-dimethoxyphenyl)-3-dodecanone and ellagic acid, respectively (at pCa 6.2). A similar effect was observed in cardiac SR microsomes (59.5 +/- 7.4% and 45.1 +/- 6.7) with 30 micromol/l 1-(3,4-dimethodoxyphenyl)-3-dodecanone and ellagic acid, respectively. 1-(3,4-Dimethoxyphenyl)-3-dodecanone increased Ca2+ storage by cardiac SR microsomes mainly at high [Ca2+] with a 57% increase of Vmax, whereas ellagic acid increased Vmax to a smaller extent (22%) and stimulated Ca2+ uptake at lower [Ca2+] with a leftward-shift of the pCa/ATPase relationship by pCa 0.24. Ellagic acid also differed from 1-(3,4-dimethoxylphenyl)-3-dodecanone in that it produced a Ca2+ sensitizing effect only in cardiac SR microsomes (by pCa 0.3) whereas 1-(3,4-dimethoxyphenyl)-3-dodecanone stimulated the ATPase, at saturating Ca2+, in both cardiac and skeletal muscle SR vesicles. It is suggested that 1-(3,4-dimethoxyphenyl)-3-dodecanone stimulates directly the Ca2+-ATPase activity, in contrast to ellagic acid which enhances the cardiac SR-Ca2+ uptake by interacting with phospholamban, as confirmed by the lack of additive effect between ellagic acid and monoclonal antibodies raised against phospholamban. 1-(3,4-dimethoxyphenyl)-3-dodecanone and ellagic acid constitute attractive pharmacological tools to investigate the functional consequences of enhancing SR Ca2+, uptake by affecting different mechanisms.
Berrebi-Bertrand
I
I
SmithKline Beecham Laboratoires Pharmaceutiques, Saint-Grégoire, France.
Lahouratate
P
P
Lahouratate
V
V
Camelin
J C
JC
Guibert
J
J
Bril
A
A
D000818:Animals; D000840:Anisoles / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004285:Dogs; D004610:Ellagic Acid / Q000494:pharmacology*; D066298:In Vitro Techniques; D007659:Ketones / Q000494:pharmacology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D000099211:Phospholamban
D000840:Anisoles; D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D004610:Ellagic Acid; D007659:Ketones; D000099211:Phospholamban; C108161:1-(3,4-dimethoxyphenyl)-3-dodecanone