Short Communication
Genetic Ablation of L-Type Ca
2
Channels Abolishes
Depolarization-Induced Ca
2
Release in Arterial
Smooth Muscle
Miguel Ferna ´ndez-Tenorio,* Patricia Gonza ´lez-Rodríguez,* Cristina Porras, Antonio Castellano,
Sven Moosmang, Franz Hofmann, Juan Uren ˜a, Jose ´ Lo ´pez-Barneo
Rationale: In arterial myocytes, membrane depolarization-induced Ca
2
release (DICR) from the sarcoplasmic
reticulum (SR) occurs through a metabotropic pathway that leads to inositol trisphosphate synthesis indepen-
dently of extracellular Ca
2
influx. Despite the fundamental functional relevance of DICR, its molecular bases
are not well known.
Objective: Biophysical and pharmacological data have suggested that L-type Ca
2
channels could be the sensors
coupling membrane depolarization to SR Ca
2
release. This hypothesis was tested using smooth muscle–selective
conditional Ca
v
1.2 knockout mice.
Methods and Results: In aortic myocytes, the decrease of Ca
2
channel density was paralleled by the disappearance
of SR Ca
2
release induced by either depolarization or Ca
2
channel agonists. Ca
v
1.2 channel deficiency resulted
in almost abolition of arterial ring contraction evoked by DICR. Ca
2
channel–null cells showed unaltered
caffeine-induced Ca
2
release and contraction.
Conclusion: These data suggest that Ca
v
1.2 channels are indeed voltage sensors coupled to the metabolic
cascade, leading to SR Ca
2
release. These findings support a novel, ion-independent, functional role of
L-type Ca
2
channels linked to intracellular signaling pathways in vascular myocytes. (Circ Res. 2010;106:
1285-1289.)
Key Words: membrane depolarization
Ca
2+
release
Ca
v
1.2 channel knockout
arterial smooth muscle
voltage sensors
T
he rise of cytosolic Ca
2+
concentration required for
vascular smooth muscle (VSM) contraction is classi-
cally considered to be attributable to either transmembrane
Ca
2+
influx through voltage- and/or receptor-operated
channels or to Ca
2+
release from the sarcoplasmic reticu-
lum (SR). However, in recent years a new SR Ca
2+
release
mechanism, depolarization-induced Ca
2+
release (DICR),
has been observed.
1–4
DICR refers to Ca
2+
release from
the SR in the absence of any transmembrane Ca
2+
influx
and takes place by means of a metabotropic pathway that
involves G protein/phospholipase C activation and subse-
quent synthesis of inositol 1,4,5-trisphosphate.
5–7
Despite the fundamental biological and pathophysiolog-
ical implications of DICR,
7–10
its underlying molecular
mechanisms are poorly known. Some G protein– coupled
receptors (GPCRs) have been proposed to have intrinsic
voltage sensitivity and act as “voltage sensors” for
DICR.
7,11
However the intrinsic voltage-sensitivity of
GPCRs cannot fully account for DICR because it is
observed in the absence of GPCR ligands and is inhibited
by organic Ca
2+
channel blockers.
3
Moreover, Ca
2+
re-
lease can be triggered by Ca
2+
channel agonists in the
absence of membrane potential changes, thus suggesting
that sensitivity of the GPCR or the phosphatidylinositol
cascade to depolarization is not the primary cause of
DICR.
3,8
We have proposed that voltage-gated Ca
2+
chan-
nels are the sensors for DICR and coined the term “calcium
channel–induced Ca
2+
release” (CCICR) for this novel
form of plasma membrane-SR interaction in VSM.
3,12
A critical experimental test necessary for establishing
the actual involvement of Ca
2+
channels in coupling
membrane potential to SR Ca
2+
release requires the study
Original received November 28, 2009; revision received March 3, 2010; accepted March 4, 2010.
From the Instituto de Biomedicina de Sevilla (M.F.-T., P.G.-R., C.P., A.C., J.U., J.L.-B.). Hospital Universitario Virgen del Rocío/CSIC/Universidad
de Sevilla, Spain; and FOR 293 and Institut fu ¨r Pharmakologie und Toxikologie (S.M., F.H.), Technische Universita ¨t Mu ¨nchen, Germany.
*Both authors have contributed equally to this work.
Correspondence to Dr Jose ´ Lo ´pez-Barneo, Instituto de Biomedicina de Sevilla, Edificio de Laboratorios, 2 planta, Hospital Universitario Virgen del
Rocío, Avenida Manuel Siurot s/n, 41013 Sevilla, Spain. E-mail lbarneo@us.es
© 2010 American Heart Association, Inc.
Circulation Research is available at http://circres.ahajournals.org DOI: 10.1161/CIRCRESAHA.109.213967
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