title: Vasopressin-induced activation of human blood platelets: prominent role of Mg2+.
abstract: Arginine-vasopressin (AVP) caused a marked shape change reaction and rise in [Ca2+]i in human blood platelets only when the extracellular buffer contained Mg2+ or Ca2+. At physiological concentrations of the cations the potency of AVP was higher in the presence of Mg2+ than of Ca2+. The amplitude of the shape change reaction was also greater with Mg2+ than with Ca2+, although the [Ca2+]i-rise was slightly more marked with extracellular Ca2+. The concentration of Mg2+ at which AVP showed half of its maximal effects was below the physiological plasma level of the cation, whereas the corresponding value for Ca2+ was higher. Addition of Ca2+ to the Mg2+ containing medium did not further enhance the action of AVP on platelet shape. In platelet-rich plasma the potency and efficacy of AVP in causing a shape change were similar in the presence and absence of EGTA, whereas with EDTA in the medium AVP had no effect. In conclusion, Mg2+ has an essential physiological role in AVP-induced platelet activation, which is brought about partly by release of intracellular calcium and partly by some other intracellular mechanism.
authors.forename: P
authors.initials: P
authors.lastname: Erne
authors.forename: A
authors.initials: A
authors.lastname: Pletscher
mesh_terms: D001127:Arginine Vasopressin / Q000494:pharmacology*; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000097:blood; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D008274:Magnesium / Q000097:blood / Q000502:physiology*; D011945:Receptors, Angiotensin / Q000502:physiology; D017483:Receptors, Vasopressin
chemical_list: D011945:Receptors, Angiotensin; D017483:Receptors, Vasopressin; D001127:Arginine Vasopressin; D004492:Edetic Acid; D008274:Magnesium; D002118:Calcium