Peptides 26 (2005) 1369–1382
Tachykinin peptides and receptors: Putting amphibians
into perspective
Lu Liu
∗
, Elizabeth Burcher
Department of Physiology and Pharmacology, School of Medical Sciences, University of New South Wales,
Sydney 2052, Australia
Available online 21 April 2005
Abstract
The tachykinins form one of the largest peptide families in nature. In this review, we describe the comparative features of the tachykinin
peptidesandtheirreceptors, focusingparticularly onamphibians. Wealso summarize our systematic studies of the localization, characteristics,
and actions of bufokinin, a toad substance P-related peptide, in its species of origin. In addition, we discuss the establishment of multiple
isoforms of the NK
1
-like receptor in the toad, and their structure, pharmacology and tissue distributions. We conclude that tachykinin peptides
and receptors are well conserved in terms of their structures, physiological functions and coupling mechanisms during tetrapod evolution.
© 2005 Elsevier Inc. All rights reserved.
Keywords: Tachykinins; Bufokinin; Tachykinin receptors; Amphibian; Intestine; Cardiovascular system
1. Overview
1.1. Introduction
The tachykinin family is phylogenetically ancient and
has been well conserved throughout evolution. Numerous
structurally related peptides have been isolated from mam-
mals, birds, reptiles, amphibia and fish [18,38,42,97] as well
as from invertebrates [95]. In this review, we give a brief
overview of the tachykinin system, including the compar-
ative features of the tachykinin peptides. We then discuss
the distribution, action and structure-activity relationship of
tachykinin peptides in amphibians, and the pharmacological
andmolecularcharacteristics of the amphibiantachykininre-
ceptors.Ourrecent workin the intestine of thecanetoad Bufo
marinushasuncoveredanoveltachykininpeptide,bufokinin,
structurally related to substance P (SP) [21], elucidated the
physiological actions of bufokinin in its species of origin
[72–74] and cloned three isoforms of bufokinin-preferring
tachykinin bNK
1
like receptor in the toad brain and intestine
[69]. Emphasis is placed on our own studies with bufokinin,
∗
Corresponding author. Fax: +61 2 93851059.
E-mail address: Lu.Liu@unsw.edu.au (L. Liu).
and on others’ studies with tachykinins in amphibian
systems.
1.2. The tachykinin peptides
Tachykinins are a family of closely related peptides that
are actively involved in the central and peripheral nervous
systems as well as in the cardiovascular and immune systems
ofbothlowerandadvancedlifeforms.Tachykininshavebeen
isolated from virtually all animals ranging from invertebrates
up to mammals. Many important early advances were made
by studying non-mammalian systems including octopus and
amphibia,andthegreatcontributionstothisfieldbyErspamer
and colleagues are acknowledged [25,97].
In mammals, tachykinins act as neurotransmitters,
paracrine or endocrine factors and neuroimmunomodulators
and have roles in the nervous system, gastrointestinal tract
and cardiovascular system.Important actions include vasodi-
latation, plasma extravasation, smooth muscle contraction,
secretion, neuronal excitation and processing of sensory
information; they also have immune and pro-inflammatory
actions [36,85]. For many years, SP, neurokinin A (NKA),
neurokinin B (NKB) and two elongated versions of NKA,
neuropeptide ␥ (NP␥) and neuropeptide K (NPK) were
0196-9781/$ – see front matter © 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.peptides.2005.03.027