Low [Mg(2+)](o) induces contraction and [Ca(2+)](i) rises in cerebral arteries: roles of ca(2+), PKC, and PI3.

Removal of extracellular Ca(2+) concentration ([Ca(2+)](o)) and pretreatment of canine basilar arterial rings with either an antagonist of voltage-gated Ca(2+) channels (verapamil), a selective antagonist of the sarcoplasmic reticulum Ca(2+) pump [thapsigargin (TSG)], caffeine plus a specific antagonist of ryanodine-sensitive Ca(2+) release (ryanodine), or a D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)]- mediated Ca(2+) release antagonist (heparin) markedly attenuates low extracellular Mg(2+) concentration ([Mg(2+)](o))-induced contractions. Low [Mg(2+)](o)-induced contractions are significantly inhibited by pretreatment of the vessels with Gö-6976 [a protein kinase C-alpha (PKC-alpha)- and PKC-betaI-selective antagonist], bisindolylmaleimide I (Bis, a specific antagonist of PKC), and wortmannin or LY-294002 [selective antagonists of phosphatidylinositol-3 kinases (PI3Ks)]. These antagonists were also found to relax arterial contractions induced by low [Mg(2+)](o) in a concentration-dependent manner. The absence of [Ca(2+)](o) and preincubation of the cells with verapamil, TSG, heparin, or caffeine plus ryanodine markedly attenuates the transient and sustained elevations in the intracellular Ca(2+) concentration ([Ca(2+)](i)) induced by low-[Mg(2+)](o) medium. Low [Mg(2+)](o)-produced increases in [Ca(2+)](i) are also suppressed markedly in the presence of Gö-6976, Bis, wortmannin, or LY-294002. The present study suggests that both Ca(2+) influx through voltage-gated Ca(2+) channels and Ca(2+) release from intracellular stores [both Ins(1,4,5)P(3) sensitive and ryanodine sensitive] play important roles in low-[Mg(2+)](o) medium-induced contractions of isolated canine basilar arteries. Such contractions are clearly associated with activation of PKC isoforms and PI3Ks.