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Departments of 1 Physiology and Pharmacology, 2 Anesthesiology, and 3 Medicine, and 4 Center for Cardiovascular and Muscle Research, Health Science Center at Brooklyn, State University of New York, Brooklyn, New York 11203
Removal of extracellular
Ca2+ concentration ([Ca2+]o) and
pretreatment of canine basilar arterial rings with either an antagonist of voltage-gated Ca2+ channels (verapamil), a selective
antagonist of the sarcoplasmic reticulum Ca2+ pump
[thapsigargin (TSG)], caffeine plus a specific antagonist of
ryanodine-sensitive Ca2+ release (ryanodine), or a
D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]- mediated
Ca2+ release antagonist (heparin) markedly attenuates low
extracellular Mg2+ concentration
([Mg2+]o)-induced contractions. Low
[Mg2+]o-induced contractions are
significantly inhibited by pretreatment of the vessels with
Gö-6976 [a protein kinase C-
(PKC-
)- and PKC-
I-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 [Mg2+]o in a concentration-dependent manner.
The absence of [Ca2+]o and preincubation of
the cells with verapamil, TSG, heparin, or caffeine plus ryanodine
markedly attenuates the transient and sustained elevations in the
intracellular Ca2+ concentration
([Ca2+]i) induced by
low-[Mg2+]o medium. Low
[Mg2+]o-produced increases in
[Ca2+]i are also suppressed markedly in the
presence of Gö-6976, Bis, wortmannin, or LY-294002. The present
study suggests that both Ca2+ influx through voltage-gated
Ca2+ channels and Ca2+ release from
intracellular stores [both Ins(1,4,5)P3
sensitive and ryanodine sensitive] play important roles in
low-[Mg2+]o medium-induced contractions of
isolated canine basilar arteries. Such contractions are clearly
associated with activation of PKC isoforms and PI3Ks.
canine basilar arteries; extracellular magnesium concentration deficiency; calcium influx; intracellular calcium release; protein kinase C; phosphatidylinositol-3 kinase
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