Endothelin-3, Ca2+ mobilization and cyclic GMP content in human platelets

Area of Science:

• Biochemistry
• Cell Biology
• Pharmacology

Background:

• Platelet activation involves complex calcium (Ca2+) signaling pathways.
• Endothelin-3 is known to affect platelet function, but its precise mechanism is debated.
• Cyclic GMP (cGMP) plays a crucial role in regulating intracellular calcium levels in various cell types.

Purpose of the Study:

• To investigate the role of cyclic GMP (cGMP) in mediating the effects of endothelin-3 on platelet calcium mobilization.
• To determine if endothelin-3-induced changes in platelet Ca2+ are linked to alterations in cGMP levels and Ca2+ pump activity.

Main Methods:

• Platelet aggregation assays measuring Ca2+ mobilization in response to thrombin.
• Measurement of cGMP accumulation in platelets treated with endothelin-3 and phosphodiesterase inhibitors (M&B-22948).
• Assessment of ATP-dependent 45Ca2+ uptake in platelet membrane vesicles to evaluate Ca2+ accumulating pump activity.

Main Results:

• cGMP-elevating agents, including sodium nitroprusside and M&B-22948, reduced thrombin-induced Ca2+ mobilization.
• Endothelin-3 induced a dose-dependent accumulation of cGMP when phosphodiesterases were inhibited.
• cGMP significantly decreased the rate and plateau of ATP-dependent 45Ca2+ uptake, indicating inhibition of Ca2+ accumulating pumps.
• Combined treatment with endothelin-3 and cGMP-elevating agents further reduced thrombin-evoked Ca2+ release.

Conclusions:

• Endothelin-3's effect on platelet calcium release may be mediated, in part, by an increase in intracellular cGMP levels.
• Elevated cGMP content likely contributes to the observed decrease in Ca2+ accumulating pump activity.
• These findings suggest a novel mechanism involving cGMP in endothelin-3-induced platelet calcium store depletion.