Evidence for an inotropic positive action of cGMP during excitation–contraction coupling in frog sartorius muscle

Abstract

Within the realm of the general hypothesis concerning the role of cGMP on intracellular calcium regulation in biological systems, we have investigated the action of cyclic nucleotides during excitation-contraction coupling in frog sartorius muscle. Our data show that several guanosine nucleotides (GTP, GDP, dibutyryl-cGMP) can increase the isometric twitch tension with a maximum increase of 40% in the muscles treated with cGMP. This increase is completely independent of external Ca2+ concentration. The use of dantrolene sodium (known to inhibit calcium release from sarcoplasmic reticulum) results in a decrease in the twitch tension with a contemporary decrease in the intracellular levels of cGMP; whereas, the addition of cGMP to the muscles treated with dantrolene antagonizes, at least partially, the effect of the drug on tension development. Finally, in chemically skinned muscles, cGMP induces a reversible contracture equal to approximately one-half of that evoked by 10(-4) M Ca2+.

New Insights into the Relationship between mIGF-1-Induced Hypertrophy and Ca2+ Handling in Differentiated Satellite Cells

“…This evidence might explain the potentiation induced in the MLC/mIGF-1 transgenic mice by ATP and GTP, which induced higher and more rapid Ca 2+ responses. In addition, considering that GTP can also potentiate muscle activity [43], [44], we can hypothesize that the repetitive contractions induced in the mIGF-1 transgenic mice might evoke a ‘potentiation effect’ higher than that obtained in the wild-type muscles. Del Prete and colleagues [8] showed that in MLC/mIGF-1 transgenic mice, the fast-twitch fibres of the extensor digitorum longus had increased absolute tetanic force and absolute maximum power, with respect to those of the wild-type extensor digitorum longus.…”

Functional aspects of calcium transport in sarcoplasmic reticulum vesicles derived from frog skeletal muscle treated with saponin

“…The muscles were immersed in Ringer solution, mounted on a recording apparatus (Mancinelli et al, 1983) and incubated for 30 rein in a solution containing diffeient conientrations (10, 25, 50 or 100 ~g ml -1) of saponin. At different time intervals (1, 10, 20, or 30 rein), a series of rive twitches at a frequency of 1 Hz was obtained.…”

Extracellular guanosine‐5′‐triphosphate modulates myogenesis via intermediate Ca2+‐activated K+ currents in C2C12 mouse cells

“…In muscular tissue, extracellular GTP affects different activities, such as the development of isometric twitch tension (Mancinelli et al 1983) or contractility of muscles involved in the backward swimming of Paramecium tetraurelia (Clark et al 1997; Mimikakis & Nelson, 1998). In vitro studies on C2C12, a skeletal muscle cell line widely used as a myogenic model, show that external GTP promotes a significant increase in intracellular calcium ([Ca 2+ ] i ) via two different mechanisms involving specific sites in the cell membrane (Pietrangelo et al 2002).…”