Smooth Myocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 387

Tabl e 8. 3. Calcium signals regulated directly or indirectly by IP 3 Rs in smooth myocytes
(Source: [ 717 ]; Ca V : voltage-dependent Ca 2 + channel; NEx: Na + -Ca 2 + exchanger; NSCC: non-
selective cation channel; RyR: ryanodine-sensitive Ca 2 + release channel; SOC: store-operated
Ca 2 + channel; TRPC: transient receptor potential canonical channel; TRPM: melastatin-related
transient receptor potential channel).

Calcium Frequency Rise Decay Spatial Involved

Ca 2 + signals (Hz) time half-time spread

(s) (s) ( m) channels

Flash 0.2-0.5 0.2-0.8 0.5-1.5 Ca V ,RyR

Global Ca V , NSCC,

spread RyR, SOC

TRPC1/3,
TRPM4

Oscillation 0.07-0.4 2-6 3-18 RyR,

TRPC6

Puff 0.02-0.04 0.06-0.16 0.11-0.25 1.89-2.51 RyR

Ripple 0.05-0.19 1-2 4-6

Spark 0.07-0.59 0.01-0.07 0.03-0.15 0.52-4.7 RyR

Wave 0.04-1.41 0.5-2 2-10 8.8-50 Ca V ,

NSCC, NEx,
RyR, SOC

Plasmalemmal Gq/11-coupled receptors stimulate phospholipase-C that
hydrolyzes plasmalemmal phosphatidylinositol (4,5)-bisphosphate and generates
diacylglycerol and inositol (1,4,5)-trisphosphate.
Inositol trisphosphate receptors constitute a set of tetrameric intracellular Ca 2 +
release channels on the endoplasmic reticulum membrane that generate Ca 2 +
signals (Vol. 3 - Chap. 3. Main Classes of Ion Channels and Pumps). Three
IP 3 R isoforms (IP 3 R1-IP 3 R3; Table 8.4 ) encoded by distinct genes are responsible
for signaling differences with given frequencies, amplitudes, and spatiotemporal
properties. These 3 isoforms are synthesized in smooth myocytes. Subtype IP 3 R1 is
the predominant isoform in vascular smooth myocytes; IP 3 R2 and IP 3 R3 densities
are higher in proliferating vascular smooth myocytes [ 717 ]. In the tracheal smooth
muscle, IP 3 R3 is the principal isoform, IP 3 R1 and IP 3 R2 being also expressed [ 717 ].
The cytosolic N-terminus possesses an IP 3 -binding domain, a suppressor motif
that inhibits IP 3 binding, and a regulatory sequence with binding sites for ATP and
Ca 2 + ion as well as phosphorylation sites and a coupling region for interacting with
transient receptor potential canonical (TRPC) channels [ 717 ]. The transmembrane
region and cytosolic C-terminus enable IP 3 R tetramerization.