Low [Mg2+](o) induces contraction of cerebral arteries: roles of tyrosine and mitogen-activated protein kinases

The present study was designed to investigate the mechanism of action of lo w extracellular magnesium ion concentration ([Mg2+](o)) on isolated canine basilar arteries and single cerebral vascular smooth muscle cells from thes e arteries. Low-[Mg2+](o)medium (0-0.6 mM) produces endothelium-independent contractions in isolated canine basilar arteries in a concentration-depend ent manner; the lower the concentration of [Mg2+](o), the stronger the cont ractions. The low-[Mg2+](o) medium-induced contractions are significantly a ttenuated by pretreatment of the arteries with low concentrations of either SB-203580, U-0126, PD-98059, genistein, or an Src homology 2 (SH2) domain inhibitor peptide. IC50 levels obtained for these five antagonists are cons istent with reported inhibitor constant (K-i) values for these tyrosine kin ase and mitogen-activated protein kinase (MAPK) antagonists. Low-[Mg2+](o) medium (0-0.6 mM) produces transient intracellular calcium ion concentratio n ([Ca2+](i)) peaks followed by a slow, sustained, and elevated plateau of [Ca2+](i) in primary single smooth muscle cells from canine basilar arterie s. Low-[Mg2+](o) medium induces rapid and stable increases in [Ca2+](i); th ese increases are inhibited markedly in the presence of either SB-203580, U -0126, PD-98059, genistein or a SH2 domain inhibitor peptide. Several speci fic antagonists of known endogenously formed vasoconstrictors do not inhibi t or attenuate either the low-[Mg2+](o)-induced contractions or the elevati on of [Ca2+](i). The present study suggests that activation of several cell ular signaling pathways, such as protein tyrosine kinases (including the Sr c family) and MAPK, appears to play important roles in low[ Mg2+](o)-induce d contractions and the elevation of [Ca2+](i) in smooth muscle cells from c anine basilar arteries.