Effect of extracellular Mg2+ concentration on agonist-induced cytosolic free Ca2+ transients

The modulating effects of extracellular Mg2+ concentration ([Mg2+]o) on vascular contraction are well known. In the present study it was tested how the changes in cytosolic free Ca2+ concentration ([Ca2+]i) induced by various agonists are modified by changes in [Mg2+]o. Extracellular Mg2+ deprivation increased the [Ca2+]i response to arginine vasopressin, to angiotensin II and to thapsigargin, but not to 5-hydroxytryptamine and noradrenaline. Withdrawal of extracellular Ca2+ revealed that extracellular Mg2+ deprivation increased Ca2+ influx, but not Ca2+ release from cellular stores. The findings demonstrate that different responses of [Ca2+]i to agonists may underlie the modulating effect of [Mg2+]o on vascular contraction.