Smooth Myocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 447

Table 8.28. Va soactive peptide receptors and their main targeted G proteins (Sou rce: [ 831 ]).

Type Main transducer

Galanin receptors

GalR1/R3 Gi/o

GalR2 Gi/o, Gq/11

Neuromedin-U receptors

NMU 1 / 2 Gq/11

Relaxin peptide family receptors

RXFP 1 / 2 Gs, Gi/o

RXFP 3 / 4 Gi/o

Tachykinin receptors

NK 1 Gq/11 (substance-P > neurokinin-A > neurokinin-B)

NK 2 Gq/11 (neurokinin-A > neurokinin-B > substance-P)

NK 3 Gq/11 (neurokinin-B > neurokinin-A > substance-P)

interacts with G-protein-coupled relaxin-insulin-like family peptide receptors
RXFP 1 (LGR7) and RXFP 2 (LGR8) used by insulin-like peptide-3 and -7
(Table 8.28 ). Relaxin receptors exist in the heart, smooth muscle, connective tissue,
and central and autonomous nervous systems.

Nociceptin

Nociceptin is a potent peptidic vasodilator that targets nociceptin receptor, i.e., -

opioid receptor KOR3 (a.k.a. Nop1, Op 4 , and opiate receptor-like ORL1 or OpRL1).
It has a direct effect on smooth myocytes. It may also act via the endothelium, i.e.,
the NO-cGMP pathway. In cultured endothelial cells, liganded KOR3 activates the
mitogen-activated protein kinase cascade [ 832 ].
In the human trigeminal ganglion, nociceptin colocalizes with calcitonin
gene-related peptide, substance-P, nitric oxide synthase, or pituitary adenylate
cyclase-activating peptide [ 833 ]. Nociceptin is not synthesized in human cerebral
blood vessels. On the other hand, opioid KOR3 receptor is synthesized in vascular
endothelial cells (of rat brain microvessels as well as human aortic artery and
umbilical vein) [ 832 ].

κ

Urocortin-1

Urocortin-1 and corticotrophin-releasing factor bind to receptors CRF 1 and CRF 2
with high affinity, whereas urocortin-2 and -3 are selective for CRF 2 receptors.
Receptor CRF 2 have been identified in vascular smooth myocytes in humans.
All urocortins cause a potent vasodilation, independently of the endothelium [ 812 ].