An Introduction to Vascular Biology
Second edition
Vascular biology is an exciting and rapidly advancing area of medical research, with many new
and emerging pathophysiological links to an increasing number of diseases. This updated and
expanded new edition takes full account of these developments and conveys the basic science
underlying a wide range of clinical conditions, including atherosclerosis, hypertension, diabetes
and pregnancy. As with the Wrst edition, the publication provides an introductory account of
vascular biology before leading on to explain mechanisms involved in disease processes. Other
emerging topics include the role of nitric oxide and apoptosis in vascular biology. The breadth
and range of subjects covered in this new edition do full justice to this increasingly important
area of clinical research and medicine. This multidisciplinary approach will suit the needs of all
those who are new to the Weld or working in one small area, with a need to get the wider picture,
and also for those seeking to refresh their knowledge with the very latest advances from basic
science through to clinical practice.
Features of the new edition
∑ All chapters fully updated and expanded, including up-to-date references
∑ Includes several new clinical chapters
∑ Covers new and emerging areas of research
∑ Integrates basic science and clinical practice
Reviews of the Wrst edition
‘I recommend this book to those seeking an introductory overview into this exciting and rapidly
burgeoning area. The authors provide an up-to-date interpretation of vascular biology and how
this might relate to disease; the Wgures are excellent; and the references oVer access to further
sources of information.’ journal of the royal society of medicine
‘. . . it makes excellent reading . . . for readers who are interested in gaining fundamental
understanding of this critical area. I believe the book oVers an excellent pathway towards this
goal.’ british journal of surgery
‘It is well written, with the correct balance of Wgures, tables and text, and also well referenced . . .
I warmly recommend it.’ biomedical sciences
MMMM
An Introduction to

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Contents
List of contributors vii
Preface xiii
Part I
Basic science 1
1 Vascular tone 3
Alun D. Hughes
2 Vascular compliance 33
Brenda A. Kelly and Philip Chowienczyk
3 Flow-mediated responses in the circulation 49
Lucilla Poston
4 Neurohumoral regulation of vascular tone 70
Kirsty M. McCulloch and John C. McGrath
5 Angiogenesis: basic concepts and the application of gene therapy 93
John W. Quarmby and Alison W. Halliday
6 The regulation of vascular smooth muscle cell apoptosis 114
Nicola J. McCarthy and Martin R. Bennett
7 Wound healing: laboratory investigation and modulating agents 129
Nick L. Occleston, Julie T. Daniels and Peng T. Khaw
Part II Pathophysiology: mechanisms and imaging 167
8 Genes for hypertension 169
Mark Caulfield, Joanne Knight, Suzanne O’Shea, Gerard Gardner and Patricia Munroe
9 The endothelium in health and disease 186

Level 6, Box 110
Addenbrooke’s Hospital
Hills Road, Cambridge CB2 2QQ

Mark CaulWeld MD FRCP
The Cardiovascular Genetics Group
Department of Clinical Pharmacology
St Bartholomew’s and The Royal London
School of Medicine and Dentistry
Charterhouse Square
London EC1M 6BQ

Norman Chan MB ChB MRCP DCH
Centre for Clinical Pharmacology
The Rayne Institute
University College London
5 University Street
London
WC1E 6JJ

Philip Chowienczyk
Department of Clinical Pharmacology
Ground Floor
St Thomas’ Hospital
London SE1 7EH

Julie T. Daniels
Wound Healing Research Unit
Department of Pathology
Institute of Ophthalmology and

University of Birmingham
Birmingham B15 2TT

Tim Higenbottam MA MD DSc FRCP
Clinical Sciences
AstraZeneca R&D Charnwood
Bakewell Road
Loughborough
Leicestershire LE11 5RH

Alun D. Hughes
Clinical Pharmacology
NHLI, Imperial College
St Mary’s Hospital
London W2 1NY

Beverley J. Hunt MD FRCP FRCPath
Departments of Haematology and
Rheumatology
Guy’s and St Thomas’ Trust
Lambeth Palace Road
London SE1 7EH

Karen M. Jurd BSc (Hons) PhD
Principal Scientist, Protection and
Performance Department Centre for
Human Sciences
DERA Alverstoke
Gosport
Brenda A. Kelly

Floor F, Medical School
University of SheYeld
Beech Hill Road
SheYeld S10 2RX

viii List of contributors
Nicola J. McCarthy
Unit of Cardiovascular Medicine
Addenbrooke’s Centre for Clinical
Investigation
Level 6, Box 110
Addenbrooke’s Hospital
Hills Road, Cambridge CB2 2QQ

Kirsty M. McCulloch
Department of Pharmacology
Quintiles Ltd
Research Avenue South
Heriot-Watt University Research Park
Riccarton, Edinburgh
EH14 4AP

John C. McGrath
Head of Division of Neurosciences and
Biomedical Systems
Institute of Biomedical and Life Sciences
University of Glasgow
West Medical Building
Glasgow G12 8QQ


Guy’s, King’s and St Thomas’ School of
Medicine, and Centre for Cardiovascular
Biology and Medicine
St Thomas’ Hospital
London SE1 7EH

Janet T. Powell PhD MD
Professor of Vascular Biology
Department of Vascular Surgery
Imperial College School of Medicine
Charing Cross Hospital
Fulham Palace Road
London W6 8RF

ix List of contributors
John W. Quarmby
Department of Vascular Surgery
St George’s Hospital
Blackshaw Road
London SW17 0RE
Marlene L. Rose
Professor of Transplant Immunology
National Heart and Lung Institute
Imperial College School of Medicine
Heart Science Centre
HareWeld Hospital
HareWeld, Middlesex UB9 6JH

James H.F. Rudd MRCP
Division of Cardiovascular Medicine


John E. Tooke
Department of Vascular Medicine
Postgraduate Medical School
Barrack Road
Exeter EX2 5AW

Patrick Vallance MRCP MD FRCP
FmedSci
Centre for Clinical Pharmacology
The Rayne Institute
University College London
5 University Street
London WC1E 6JJ

Peter L. Weissberg MD FRCP FMedSci
FESC
Division of Cardiovascular Medicine
Addenbrooke’s Centre for Clinical
Investigation
Addenbrooke’s NHS Trust
Hills Road
Cambridge CB2 2QQ

x List of contributors
David Williams MRCP
Department of Obstetrics and
Gynaecology
Imperial College School of Medicine
Chelsea and Westminster Hospital

Clinical Pharmacology, NHLI, Imperial College, St Mary’s Hospital, London
Introduction
This chapter provides an overview of how vascular smooth muscle cells produce
force and how this process is regulated. An overview inevitably involves generaliz-
ations and this tends to obscure the considerable diversity that exists in vascular
smooth muscle. Such diversity is unsurprising if one recalls the variety of func-
tions performed by blood vessels. Large arteries act as elastic conduits, smaller
arteries regulate the distribution of blood Xow, the microvasculature largely
determines vascular resistance and Xuid exchange, while the venous system under-
takes a capacitive role and governs venous return to the heart. When these
diVerences are compounded with the diVerences in behaviour required from
blood vessels supplying diVerent tissues, one can see that smooth muscle diversity
is a positive asset that allows appropriate responses in a particular circumstance.
Owing to space constraints I have not attempted to provide comprehensive
source references in this chapter. Instead, recent reviews have been cited and these
should be referred to for more detailed information regarding a particular topic
and original sources.
Types of stimulus for contraction and relaxation
Under physiological circumstances the primary role of diVerentiated (as opposed
to ‘synthetic’) smooth muscle is to generate force. Normally, the vascular smooth
muscle that makes up the bulk of the blood vessel wall is in a state of continual
activation. The amount of force generated by smooth muscle is Wnely regulated by
a variety of extracellular and intrinsic factors. The types of stimuli that act on
vascular smooth muscle can be grouped into Wve categories:
1. Agents acting at G protein-coupled receptors
2. Pressure/tension
3. Agents acting directly on ion channels or signalling systems
4 A. D. Hughes
4. Extracellular matrix components, cell adhesion molecules and integrins
5. Growth factors

interactions (Lefkowitz, 1998). Secondly, regulators of G-protein signalling (RGS)
proteins act to enhance the GTPase activity of  subunits (Dohlman and Thorner,
1997). A number of isoforms of both  and  subunits exist and preferential
coupling of the receptor to a speciWc  combination probably accounts for the
diversity of intracellular events generated by this signalling complex (Hildebrandt,
1997).
Pressure/tension
The ability of vascular smooth muscle to respond to increased transmural pressure
by increased tone was Wrst recognized by Bayliss in 1902. The current view is that
wall tension or stress, rather than pressure per se is the stimulus for contraction.
The balance between myogenic tone and endothelium-dependent vasodilatation
may coordinate the behaviour of arterial networks (GriYth et al., 1987). While the
myogenic response is a very important determinant of tone, perhaps particularly
in the microvasculature, the biochemical mechanisms underlying its transduction
are still poorly understood; stretch-induced production of vasoconstrictors or
Figure 1.1 Receptor (R
7
G) and associated heterotrimeric G protein. Example shown is of an
angiotensin II type 1 (AT
1
) receptor and a G protein heterotrimer. The image is based on a
model constructed by Paiva, A.C.M. Costa-Neto, C.M. & Oliveira, L. Molecular modeling and
mutagenesis studies of angiotensin II/AT
1
interaction and signal transduction. On-line
Proceedings of the 5th Internet World Congress on Biomedical Sciences ’98 at McMaster
University, Canada (available from
URL: />).
5 Vascular tone
6 A. D. Hughes

transmembranous receptors which are intrinsic tyrosine kinases. Dimerization
results in transautophosphorylation of tyrosine residues in the intracellular do-
main of the receptor and leads to recruitment and activation of a range of
signalling molecules (Hughes et al., 1996). Increasing evidence suggests an im-
portant role for tyrosine kinases in the regulation of smooth muscle tone, even in
response to classical vasoconstrictors (Hughes and Wijetunge, 1998).
Regulation of [Ca
2+
]
i
in vascular smooth muscle
The pivotal role of Ca
2+
in muscle contraction has been recognized for many years.
[Ca
2+
]
i
can rise as a consequence of an increase in inXux of extracellular Ca
2+
,
alteration in the amount of intracellularly sequestered Ca
2+
or a decrease in eZux
7 Vascular tone
of cellular Ca
2+
. In general, most contractile stimulants appear to act by altering
inXux or release of Ca
2+

proteins or to be taken up into stores (Kamishima and McCarron, 1996). Despite
this, opening of Ca
2+
channels causes [Ca
2+
]
i
to rise to micromolar levels. This is
suYcient to activate the contractile (and other) processes. There is now substantial
evidence that [Ca
2+
]
i
is compartmentalized within the cell and that localized
increases in [Ca
2+
]
i
are important to cell function, particularly regulation of ion
channel opening (Jaggar et al., 1998a).
The major Ca
2+
-permeable channel in vascular smooth muscle is the voltage-
operated calcium channel (Hughes, 1995). As its name implies, this channel is
primarily regulated by E
m
and the likelihood of the channel opening (open
probability) increases steeply with depolarization. Consequently, E
m
is an import-

arteries would be expected to be relatively depolarized as a result of ‘myogenic’
depolarization and prevailing tonic contractile inXuences such as the sympathetic
nervous system and circulating factors. Measurements of E
m
in vivo are consistent
with this, with E
m
being in the range ~ − 40 mV (Bryant et al., 1985). This has
important consequences for our understanding of the action of some drugs, e.g.
dihydropyridine, which act preferentially on depolarized cells.
[K ]
6 mmol/l
89 mVE
Resting E = ~ + 60 mV
(Nernst)
+62 mV
+150 mV
22 mV
164 mmol/l
+
[Na ]
137 mmol/l
13 mmol/l
+
[Ca ]
1.7 mmol/l
0.0001 mmol/l
+
[Cl ]
134 mmol/l

As a result of the electrical coupling a blood vessel behaves like a three-dimen-
sional electrical cable through which potential changes can propagate (Holman et
al., 1990; Tomita, 1990; Gustafsson and Holstein-Rathlou, 1999). Estimates of the
cable properties of smooth muscles vary, but values for the length constant of
electrical conduction  are generally in the range 1–2 mm. It has been suggested
that smooth muscle cells and endothelial cells may also be electrically coupled via
gap junctions in some blood vessels (Gustafsson and Holstein-Rathlou, 1999).
Major ion channel species in vascular smooth muscle
K channels
K channels make up a large family of channels encoded by multiple gene families
(Standen and Quayle, 1998). K channels consist of four  subunits that are
associated with  subunits to make a hetero-octomer (Figure 1.3). The  subunits
form the channel pore while the  subunits modify channel gating properties.
Four major types of K channel are present in vascular smooth muscle: voltage-
dependent (K
V
) channels, Ca
2+
-activated (K
Ca
) channels, inward rectiWer (K
IR
)
channels and ATP-sensitive (K
ATP
) channels. The presence of relatively large
;
(a)(c)
(b)(d)
Figure 1.3 Views of the KcsA channel tetramer, molecular surface of KcsA and contour of the pore.

Ca
channels (Table 1.1:
Calder et al., 1993).
Cl channels
Cl
−
ions are actively concentrated inside the vascular smooth muscle cell, probably
as a result of the activity of the Na-K-2Cl cotransporter and HCO
3
−
/Cl
−
exchange.
Consequently the equilibrium potential for Cl
−
ion (E
Cl
) is around − 25 mV.
Opening Cl channels will therefore depolarize smooth muscle cells. Two classes of
Cl channels have been identiWed in vascular smooth muscle – a Ca
2+
-activated Cl
channel (Cl
Ca
: Large and Wang, 1996) and volume-sensitive Cl channels
(Yamakazi et al., 1998; Lamb et al., 1999). Cl
Ca
has not been identiWed at the
molecular level, but it is a small conductance channel (Klockner, 1993), that opens
in response to a rise in [Ca

Depolarization 4-Aminopyridine, quinidine,
phenylcyclidine, tedisamil,
tetraethylammonium
K
IR
Resting membrane
potential K
+
-induced
dilatation
Depolarization Ba
2+
K
Ca
Myogenic tone
‘Brake’ on agonist-induced
depolarization
[Ca
2+
]
i
Depolarization
Thiazides
NS004
Charybdotoxin, iberiotoxin
K
ATP
Metabolic regulation of
tone
Reactive hyperaemia

benzoate
Cation channels
Receptor-operated
channels
Agonist-induced
depolarization
G protein-linked
receptors
Inorganic cations (e.g. Ni
2+
,
Gd
3+
)
Ca
2+
-activated [Ca
2+
]
i
Calcium channels
l-type Myogenic tone
Agonist-induced calcium
entry
Depolarization,
dihydropyridine agonists
(e.g. Bay K8644a)
Dihydropyridine
antagonists,
phenylalkylamines,