P2 Receptor Signaling in Motor Units in Muscular Dystrophy

The purine signaling system is represented by purine and pyrimidine nucleotides and nucleosides that exert their effects through the adenosine, P2X and P2Y receptor families. It is known that, under physiological conditions, P2 receptors play only a minor role in modulating the functions of cells and systems; however, their role significantly increases under some pathophysiological conditions, such as stress, ischemia or hypothermia, when they can play a dominant role as a signaling molecule. The diversity of P2 receptors and their wide distribution in the body make them very attractive as a target for the pharmacological action of drugs with a new mechanism of action. The review is devoted to the involvement of P2 signaling in the development of pathologies associated with a loss of muscle mass. The contribution of adenosine triphosphate (ATP) as a signal molecule in the pathogenesis of a number of muscular dystrophies (Duchenne, Becker and limb girdle muscular dystrophy 2B) is considered. To understand the processes involving the purinergic system, the role of the ATP and P2 receptors in several models associated with skeletal muscle degradation is also discussed.

Modulatory Roles of ATP and Adenosine in Cholinergic Neuromuscular Transmission

A review of the data on the modulatory action of adenosine 5’-triphosphate (ATP), the main co-transmitter with acetylcholine, and adenosine, the final ATP metabolite in the synaptic cleft, on neuromuscular transmission is presented. The effects of these endogenous modulators on pre- and post-synaptic processes are discussed. The contribution of purines to the processes of quantal and non-quantal secretion of acetylcholine into the synaptic cleft, as well as the influence of the postsynaptic effects of ATP and adenosine on the functioning of cholinergic receptors, are evaluated. As usual, the P2-receptor-mediated influence is minimal under physiological conditions, but it becomes very important in some pathophysiological situations such as hypothermia, stress, or ischemia. There are some data demonstrating the same in neuromuscular transmission. It is suggested that the role of endogenous purines is primarily to provide a safety factor for the efficiency of cholinergic neuromuscular transmission.

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.