Involvement of the TRPV1 channel in the modulation of spontaneous locomotor activity, physical performance and physical exercise-induced physiological responses

Physical exercise triggers coordinated physiological responses to meet the augmented metabolic demand of contracting muscles. To provide adequate responses, the brain must receive sensory information about the physiological status of peripheral tissues and organs, such as changes in osmolality, temperature and pH. Most of the receptors involved in these afferent pathways express ion channels, including transient receptor potential (TRP) channels, which are usually activated by more than one type of stimulus and are therefore considered polymodal receptors. Among these TRP channels, the TRPV1 channel (transient receptor potential vanilloid type 1 or capsaicin receptor) has well-documented functions in the modulation of pain sensation and thermoregulatory responses. However, the TRPV1 channel is also expressed in non-neural tissues, suggesting that this channel may perform a broad range of functions. In this review, we first present a brief overview of the available tools for studying the physiological roles of the TRPV1 channel. Then, we present the relationship between the TRPV1 channel and spontaneous locomotor activity, physical performance, and modulation of several physiological responses, including water and electrolyte balance, muscle hypertrophy, and metabolic, cardiovascular, gastrointestinal, and inflammatory responses. Altogether, the data presented herein indicate that the TPRV1 channel modulates many physiological functions other than nociception and thermoregulation. In addition, these data open new possibilities for investigating the role of this channel in the acute effects induced by a single bout of physical exercise and in the chronic effects induced by physical training.

Vasosensory responses elicited by Indian red scorpion venom last longer than capsaicin-induced responses.

The present study was conducted to compare the time-related cardiorespiratory changes occurring after the injection of Mesobuthus tamulus (BT; 1 mg/kg) venom and capsaicin (1.2 ng/kg) in the peripheral end of femoral artery in urethane anaesthetised rats. Blood pressure (BP), electrocardiogram (for heart rate; HR) and respiratory movements were recorded for 60 min after venom/capsaicin intra-arterially. Minute ventilation (MV) was computed by using appropriate calibrations. After intraarterial injection of BT venom, there was immediate (within 2 sec) increase in respiratory rate (RR) and MV which reached to 40% within 30 sec, followed by a 40% decrease in RR without any change in MV. Further, there was sustained increase in RR (50%) and MV (65%) up to 60 min. The BP began to increase at 40 sec, peaking at 5 min (50%) and remained above the initial level up to 60 min. The bradycardiac response began after 5 min which peaked (50% of the initial) at 25 min and remained at that level up to 60 min. In capsaicin treated group, there was immediate hyperventilatory (increase in RR and MV) changes within 2 sec which returned to the initial level within 2 min and remained at that level up to 60 min. The capsaicin-induced hypotensive response began within 5 sec which returned to the initial level by 5 min and remained at that level throughout. Capsaicin did not produce any change in HR. These observations suggest that intraarterial injection of BT venom produces prolonged cardiorespiratory alterations as compared to the capsaicin-induced responses.