Cytosolic free magnesium concentration in human platelets.

Although the magnesium ion (Mg2+) is considered to play an important role in cell activation, information is limited by the lack of suitable methods for measuring cytosolic free Mg2+ concentration ([Mg2+]i). We measured [Mg2+]i in resting and activated human platelets using a new fluorescent Mg(2+)-indicator, mag-fura-2. [Mg2+]i was 0.54 +/- 0.14 mM in resting platelets from 15 healthy volunteers. [Mg2+]i was elevated to 1.33 +/- 0.44 mM and 0.92 +/- 0.37 mM in platelets stimulated with thrombin and collagen, respectively. Increased Mg2+ was considered to be derived chiefly from intracellular Mg2+ mobilization. These results suggest that platelet activation is associated with the increase in [Mg2+]i. The estimation of [Mg2+]i using this method is useful for the investigation of mechanism for various cell activation.