Cardiomyocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 204

β 2-adrenergic receptors play a more modest role in regulation of cardiac inotropy

and lusitropy.
β -adrenoceptors can colocalize with NuP62 nucleoporin. In fact, Gs-coupled-

β 2-adrenoceptors, can lodge in the

nuclear membrane, at least in rodent adult ventriculocardiomyocytes [ 354 ]. Whereas
β

1- and Gi-coupled- β 3-adrenoceptors, but not β

1AR activates adenylate cyclases, β 3AR modulates transcriptional initiation.

Stimulated Band

components of its signaling pathways. Extracellular noradrenaline is taken up and
can move to the nucleus within hours.

β ARs target rRNA and mRNAs, such as transcripts of NF κ

5.3 Sarcomere

Myofibrils, formed by packed contractile proteins (actin, myosin, and associated
proteins), fill a large fraction of the cytosol, whereas the rest is occupied by other
organelles such as mitochondria.
The striated appearance of myofibers is created by a transverse pattern of
alternating dark A bands, 21 bisected by the H zone 22 with a mid M line, 23 and light
I bands, 24 divided by Z lines, or Z discs, 25 (Fig. 5.2 ).
The sarcomere (length m), the array of thick and thin filaments between

the Z lines, is the anatomical unit of muscular contraction, and the hemisarcomere
is the functional unit. Repeating sarcomere units are precisely aligned in the
cardiomyocyte.
The sarcomere length is a predictor of muscle function. Non-invasive
measurements have been developed to assess the sarcomere structure. Tissue
scattering is related to refractive index distributions associated with the morphology
and composition of the explored tissue. Sarcomere structural changes can be
monitored by optical reflectance on muscle, a strong correlation existing between
muscle optical scattering properties and sarcomere length used as a predictor of
muscle function [ 355 ]. Visualization of individual sarcomeres and analysis of their
dynamics can now be obtained owing to optical microendoscopy [ 356 ]. 26

∼ 2

21 A stands for anisotropic.
22 In German, hell: bright.
23 In German, Mittelscheibe: disc in the middle (of the sarcomere).
24 I stands for isotropic.
25 In German, Zwischenscheibe: intermediary disc (in the middle of I bands).
26 Optical microendoscope is composed of gradient refractive index microlenses (bore 350-
1,000 m). The microendoscopy associated with a laser-scanning microscope detects 2 intrinsic
optical signals: (1) autofluorescence from nicotinamide adenine dinucleotide and flavoproteins that
are concentrated in mitochondria along sarcomeric Z discs and (2) second-harmonic generation,
coherent frequency-doubling of incident light that arises from myosin rods.