Smooth Myocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 427

neural and humoral factors. In particular, mechanical signals can be transformed
into electrical cues by modulations of ion channel activity in endothelial cells and
smooth myocytes.
Membrane potential is an important determinant of vascular tone. The activity of
many ion channels (e.g., chloride and potassium channels) that is involved in setting
the membrane potential is targeted by vasoactive substances.

8.5.8.1 Vasomotion

The cGMP-dependent Ca 2 + -activated Cl − flux in vascular smooth myocytes
through bestrophins, especially bestrophin-3, is involved in the synchronization of
SMC activity, i.e., rhythmic contractions in the vascular wall, or vasomotion [ 787 ].
Vasomotion may participate in blood pressure control and optimization of transfer
between tissue and capillary blood. Vasomotion indeed enhances dialysis of the
extravascular fluid.
Bestrophin-3 localizes to both smooth muscle and endothelial cells. Bestrophin-3
resides in the sarcolemma and can be internalized [ 787 ]. Bestrophin-1 and -2
also lodge in the sarcolemma. Bestrophins may be located at the endoplasmic
reticulum where they yield countercurrent necessary for Ca 2 + release. Bestrophin-
3 supports synthesis of bestrophin-1 and -2 [ 787 ]. 68 Calcium-activated chloride
channel TMEM16, or anoctamin-1, may also contribute to vasomotion.
In small mesenteric arteries of rats, intermittent release of Ca 2 + ions from
intracellular stores activates a Ca 2 + - and cGMP-dependent Cl − channel in smooth
myocytes; the ensuing Cl − flux entrains the Ca 2 + oscillations. Bestrophin is
implicated in rhythmic, but not in tonic contractions, such as those induced by
noradrenaline and vasopressin [ 787 ].

8.5.8.2 Myogenic Response

The myogenic response is caused by a change in arterial pressure, in particular
in cerebral, coronary, and renal arteries. Blood flow autoregulation indeed results
from the ability of small resistance arteries and arterioles 69

m])
embedded within organs to reduce or increase their calibers in response to changes
in intravascular pressure. This mechanism thus maintains a constant blood flow to
organs over a given range of pressures. It was described in 1902 by Bayliss.
The myogenic response is independent of the action of the vascular endothelium.
This mechanotransduction process relies on the intrinsic property of smooth

(bore O [100

68 Similar crossinteractions at the synthesis level exist for caveolin-1 and-2 as well as connexin-37
and -40.
69 Large and mid-sized irrigation arteries carry blood to organs. Small arteries and arterioles convey
blood to the capillary bed; they distribute blood within organs.