Calmodulin Stimulation of Plasmalemmal Ca2+-Pump of Canine Aortic Smooth Muscle
作者:
C.Y. Kwan,
P. Kostka,
A.K. Grover,
J.S. Law,
E.E. Daniel,
期刊:
Journal of Vascular Research
(Karger Available online 1986)
卷期:
Volume 23,
issue 1
页码: 22-33
ISSN:1018-1172
年代: 1986
DOI:10.1159/000158622
出版商: S. Karger AG
关键词: Vascular smooth muscle;Plasma membranes;Calcium transport;Ca2+-ATPase;Calmodulin
数据来源: Karger
摘要:
Plasma-membrane-enriched fractions of canine aortic smooth muscle possess an ATP-supported Ca2+ accumulation which has an absolute requirement for Mg2+ and a high affinity for Ca2+ (Km ∼ 0.5 µM). The rate of ATP-supported Ca2+ transport is not affected by several calmodulin antagonists, but is stimulated by exogenously added calmodulin. The maximal effect of calmodulin on the rate of ATP-dependent Ca2+ transport (at 5.0 µM Ca2+) occurs at 10 µg/ml calmodulin and represents an approximately 3-fold stimulation. This calmodulin stimulation of Ca2+ transport does not require pretreatment of the membranes by EGTA and is an intrinsic property of the plasma membranes. A high-affinity Ca2+-ATPase (Km for Ca2+ ∼0.5 µM) is also present in the aortic smooth muscle plasma membrane. This high-affinity Ca2+-ATPase does not require Mg2+ for catalytic activity, but is in fact inhibited by increasing Mg2+ concentrations. Calmodulin at concentrations effective for the stimulation of the ATP-dependent Ca2+ transport has no effect on the high-affinity Ca2+-ATPase activity or on the basal ATPase activity stimulated by 5 mM Mg2+ or Ca2+. Our results indicate that isolated plasma membranes of canine aortic smooth muscle contain no endogenous calmodulin. The ability of exogenously added calmodulin to stimulate the rate of ATP-dependent Ca2+ transport by vascular smooth muscle plasma membranes suggests that calmodulin may play a role in lowering the cytoplasmic concentration of ionized calcium during vasodilatation. An Mg2+-independent, but not an Mg2+-dependent high-affinity Ca2+-ATPase, was identified in the plasma membranes. This may be separate from the plasmalemmal Ca2+
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