Endothelin-3 decreases Ca2+ uptake in platelet membrane vesicles.
To analyze the mechanisms by which endothelin-3 (ET-3) attenuates agonist-mediated Ca2+ mobilization from an internal pool, we investigated ET-3 effects on 45Ca2+ uptake in platelet membrane vesicles. They were compared to those of thapsigargin (Tg), a specific inhibitor of the dense tubule Ca2+ pumps. In the absence of ATP, ET-3 up to 1 microM did not affect the amount of Ca2+ bound to membrane sites. In the presence of ATP, ET-3 dose-dependently reduced the initial rate and the extent of Ca2+ uptake (p < 0.001). In comparison, Tg dose-dependently inhibited both the ATP-independent Ca2+ binding (p < 0.001) and the ATP-dependent Ca2+ accumulation (p < 0.001), with half-maximal effects at 7 nM. Pretreatment with 1 microM ET-3 decreased the inhibitory effect of 10 nM Tg, but only on the initial rate of ATP-dependent Ca2+ uptake (p = 0.04; n = 6). These results indicate that ET-3 is functionally coupled to Ca(2+)-ATPases of the dense tubules. Its inhibitory effects are probably due to inhibition of the catalytic cycle of the Ca2+ pumps. Such inhibition could lead to a depletion of Ca2+ stores and therefore to reduced Ca2+ release in response to agonists.
Pernollet
M G
MG
Department of Pharmacology, CNRS URA 1482, René Descartes University, Necker Medical School, Paris, France.
Astarie-Dequeker
C
C
Le Breton
G
G
Devynck
M A
MA
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D016232:Endothelins / Q000494:pharmacology*; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D016232:Endothelins; D013729:Terpenes; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D002118:Calcium