Smooth Myocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 416

ATPases exchangers ET

ANP
ADH

Na

Ca

Ca
H

PKC

H Tn

PDGF, EGF

+

ATn2

ET

+

5HT 3Na

2K

α adrenergics

PKA, PKC

Mg

3Na
Ca

ATn2

cGMP

α adrenergics

K
H

HCO3
Cl

cAMP

Cam +

K

Ca

Na 2Cl

IP3

Mg

cGMP, PKG

+

cotransporter

ET−1
ATn2
ANP
EGF

β adrenergics

PGE1

−

Fig. 8.2 Interacting cocarriers of vascular smooth myocytes: primary active ion pumps and
secondary active carriers (adapted from [ 762 ]).

Calcium is resequestered in its intracellular stores through sarco(endo)plamic
reticulum calcium ATPase (SERCA). Calcium motion from the intra- to the extra-
cellular space use pumps and exchangers. In addition, passive calcium leak from
the intracellular stores can be observed. Although translocon (a.k.a. translocator or
translocation channel) can act as a calcium leak factor in the ribosomal endoplasmic
reticulum, it is normally closed [ 760 ].
Smooth myocytes often have a graded response to membrane depolarization.
The activity of ion pumps and exchangers on the SMC membrane is modulated
by several factors, such as vasoactive substances and growth factors (Fig. 8.2 ).
Moreover, gap junctions between smooth myocytes are required.
Vasodilator and -constrictor influences are exerted upon a basal vascular tone.
A vasomotor tone is indeed spontaneously developed in most arterioles [ 763 ]. In iso-
lated arterioles and arteries, the basal tone is developed for vessel physiological
pressure [ 764 ]. In addition to the average pressure, pulsatility may be involved in
veins [ 765 ] and arteries [ 766 ].
Electrical coupling in the vessel wall associated with the vasomotor activity
can be provided by connexins between endothelial cells on the one hand, smooth
myocytes on the other (homocellular coupling), and endothelial and smooth my-
ocytes (heterocellular coupling). Calcium ions can cross gap junctions [ 767 ]. Such
processes can contribute to vasomotor response spreading. Many ion channels
(Tables 8.11 and 8.12 ) and transporters (Table 8.13 ) do not seems to be modulated
by cell tension.