The effects of phenothiazines and other calmodulin antagonists on the sarcoplasmic and endoplasmic reticulum Ca(2+) pumps.
The effects of a number of phenothiazines and other calmodulin antagonists on the Ca(2+)-ATPase activity of sarcoplasmic reticulum (SR) and endoplasmic reticulum (ER) were investigated. The drugs used in this study were trifluoperazine, calmidazolium, fluphenazine, chlorpromazine, W-7, and calmodulin-binding peptide. Our results showed that calmidazolium and calmodulin-binding peptide were the most potent inhibitors of skeletal muscle SR Ca(2+)-ATPase activity (isoform SERCA 1) (IC(50) values of 0.5 and 7 microM, respectively), while W-7 was the least potent inhibitor (IC(50), 125 microM). All of the antagonists had little effect on the cerebellar ER Ca(2+)-ATPase activity (isoform SERCA 2b), except for trifluoperazine, which had a biphasic effect, causing stimulation at low concentrations and inhibition at higher concentrations. Our results suggest that the effects of these calmodulin antagonists are independent of calmodulin and that they inhibit the Ca(2+)-ATPase in an isoform-specific manner. It was found that these antagonists inhibit the skeletal muscle isoform of the Ca(2+) pump by altering the Ca(2+) affinity and the associated Ca(2+)-binding steps, as well as possibly stabilising the E1 conformational state of the enzyme.
Khan
S Z
SZ
School of Biosciences, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK.
Longland
C L
CL
Michelangeli
F
F
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D000252:Calcium-Transporting ATPases / Q000187:drug effects* / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D005476:Fluphenazine / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D010640:Phenothiazines / Q000494:pharmacology*; D010766:Phosphorylation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D013552:Swine
D002147:Calmodulin; D007093:Imidazoles; D010640:Phenothiazines; C031938:calmidazolium; D000251:Adenosine Triphosphatases; D000252:Calcium-Transporting ATPases; D005476:Fluphenazine