Different effects of ATP on the contractile activity of mice diaphragmatic and skeletal muscles

The effects of ATP on the contractions of rat and mouse fast skeletal muscle

INTRODUCTION

The aim of this study was to compare the effects of adenosine-5'-triphosphate (ATP) and adenosine on the contractility of rodent extensor digitorum longus (EDL) muscle at normal and low temperatures.

METHODS

Contractions of rat and mouse isolated EDL were induced by either electrical stimulation (ES) or exogenous carbachol and recorded in the presence of ATP or adenosine (both at 100 μM).

RESULTS

ATP at all temperatures caused a decrease of the contractions induced by carbachol in rat and mouse EDL and ES-induced contractions in rat EDL, while it potentiated the ES-induced contractions of mouse EDL. Adenosine reduced the contractility of rat and mouse EDL evoked by ES and did not affect the carbachol-induced contractions of rat and mouse EDL at any temperature.

DISCUSSION

Under various temperature conditions, ATP inhibits pre- but potentiates postsynaptic processes in the mouse EDL; in the rat EDL ATP causes only inhibition of neuromuscular conduction. Muscle Nerve 59:509-516, 2019.

Effects of ATP and adenosine on contraction amplitude of rat soleus muscle at different temperatures

INTRODUCTION

The aim of this study was to evaluate the effects of adenosine 5'-triphosphate (ATP) and adenosine on the contractility of mammalian skeletal muscle under hypothermic conditions.

METHODS

Contractions of isolated rat soleus muscle were induced by either electrical stimulation (ES) or carbachol at physiological temperatures (37°C) and hypothermic conditions (30-14°C) and recorded in the presence of ATP, adenosine, suramin, and 8-(p-sulfophenyl)-theophylline (8-SPT).

RESULTS

At 37°C, incubation of the muscles with ATP inhibited ES-induced contractions; the inhibitory effect of ATP disappeared at 14°C. Adenosine inhibited ES-induced contractions at all temperature levels; 8-SPT fully prevented the action of adenosine. ATP and adenosine did not significantly affect carbachol-induced contractions at 37°C, while at lower temperatures ATP potentiated them. Suramin fully prevented effects of ATP.

CONCLUSIONS

ATP is involved in both pre- and postsynaptic regulation of rat soleus muscle contractility, and these processes are significantly more pronounced at low temperatures. Muscle Nerve 55: 417-423, 2017.

Opposite effect of ATP on contraction force of tonic and phasic skeletal muscles in frogs

Experiments in vitro showed that ATP and adenosine equally suppressed contractions of frog m. sartorius, which belongs to the phasic type muscles. Adenosine receptors antagonist 8-SPT abolished the effect of adenosine, but did not change the effect of ATP. This fact proves the independence of signaling pathways of these purines. ATP produced an opposite effect on the tonic muscle m. cruralis and increased the force of its contraction. Adenosine produced an inhibitory effect on the force of m. cruralis contration. In this case, 8-SPT also eliminated the effect of adenosine, but did not change the effect of ATP. The potentiating effect of ATP was blocked by suramin, a nonselective antagonist of P2 receptors, which attests to their involvement into the effects of this purine. The opposite effects of purinergic regulation reflect fundamental differences in functional organization of phasic and tonic muscular systems. It was hypothesized that the increase in contraction force under the effect of ATP is a mechanism providing maitenance of the contracted state of tonic muscle without appreciable metabolic costs.

Possible mechanisms for the effect of protein sensitization on functional properties of the isolated m. soleus and m. EDL from mice

We studied possible involvement of ATP in the influence of protein sensitization on contractile function and non-quantum secretion in the end-plate of isolated skeletal muscles from mouse leg. The dynamic vector of muscle contraction force was shown to correlate with changes in non-quantum secretion of acetylcholine under various conditions of experimental pathology. However, the degree of these changes was lower in sensitized animals. It can be hypothesized that the ATP-induced variability in functional properties of slow muscles during protein sensitization reflects the development of resistance to external loads. The adaptive changes in fast muscles during protein sensitization are not associated with the ATP-mediated mechanisms of excitation.

Extracellular ATP signaling during differentiation of C2C12 skeletal muscle cells: role in proliferation

Evidence shows that extracellular ATP signals influence myogenesis, regeneration and physiology of skeletal muscle. Present work was aimed at characterizing the extracellular ATP signaling system of skeletal muscle C2C12 cells during differentiation. We show that mechanical and electrical stimulation produces substantial release of ATP from differentiated myotubes, but not from proliferating myoblasts. Extracellular ATP-hydrolyzing activity is low in myoblasts and high in myotubes, consistent with the increased expression of extracellular enzymes during differentiation. Stimulation of cells with extracellular nucleotides produces substantial Ca(2+) transients, whose amplitude and shape changed during differentiation. Consistently, C2C12 cells express several P2X and P2Y receptors, whose level changes along with maturation stages. Supplementation with either ATP or UTP stimulates proliferation of C2C12 myoblasts, whereas excessive doses were cytotoxic. The data indicate that skeletal muscle development is accompanied by major functional changes in extracellular ATP signaling.

Effect of purinergic receptor activation on Na+-K+ pump activity, excitability, and function in depolarized skeletal muscle

Activity-induced elevation of extracellular purines and pyrimidines has been associated with autocrine and paracrine signaling in many tissues. Here we investigate the effect of purinergic signaling for the excitability and contractility of depolarized skeletal muscle. Muscle excitability was experimentally depressed by elevating the extracellular K(+) from 4 to 10 mM, which reduced the tetanic force to 24 +/- 2% of the force at 4 mM K(+). Upon addition of 1 mM ATP, however, the force recovered to 65 +/- 8% of the control force (P < 0.001, n = 5). A similar recovery was seen with ADP, but not with UTP or adenosine. The ATP-induced force recovery could be inhibited by P2Y(1) receptor antagonists (3 muM SCH-202676 or 1 muM MRS-2500). A fourfold increase in M-wave area demonstrated that the ATP-induced force recovery was associated with restoration of muscle excitability (P < 0.05, n = 4). Experiments using (86)Rb(+) as a tracer for K(+) showed that ATP also induced a twofold increase in the activity of muscle Na(+)-K(+) pumps. The force recovery and the stimulation of the Na(+)-K(+) pump activity by ATP were inhibited by 50 muM of the phospholipase C inhibitor U-73122. It is concluded that purinergic signaling can increase the Na(+)-K(+) pump activity and improve force and excitability of depolarized skeletal muscles. This novel purinergic regulation may be important for the maintenance of muscle excitability during intense exercise, where the extracellular K(+) can increase substantially.

Ovalbumin-induced sensitization affects non-quantal acetylcholine release from motor nerve terminals and alters contractility of skeletal muscles in mice

Skeletal muscles play key roles in the development of various pathologies, including bronchial asthma and several types of auto-immune disorders, e.g. polymyositis. Since most of these maladies have an immunological/allergic element, this paper is devoted to assessing the impact of immunobiological reorganization on the functional properties of isolated skeletal muscles in mice. A combination of two methods (myography and electrophysiology) was used to evaluate extensor digitorum longus (EDL) and diaphragmatic muscle (DM) in this regard. Conventional myographic technique showed that ovalbumin-induced sensitization (OS) produced different changes in the contractile properties of EDL and DM. The amplitudes of carbachol (CCh)-induced contractions increased in DM but decreased in EDL. Those changes were inversely related to OS-mediated changes of non-quantal acetylcholine (ACh) release intensity within the muscle endplate, as shown by the electrophysiologically measured H-effect. These results clearly show that OS-mediated changes of non-quantal ACh release alter the functional properties of postjunctional ACh receptors and therefore contribute to the disturbance of CCh-induced contractility of skeletal muscles. Other mechanisms of OS-mediated changes of skeletal muscle contractility are also proposed and discussed.