TRPV1 (Transient Receptor Potential Vanilloid 1) Sensitization of Skeletal Muscle Afferents in Type 2 Diabetic Rats With Hyperglycemia

The blood pressure response to exercise is exaggerated in type 2 diabetes (T2D). However, the underlying mechanisms remain unclear. It is hypothesized that one mechanism mediating the potentiated cardiovascular response in T2D is the sensitization of chemically sensitive afferent neurons by activation of metaboreceptors. To test this hypothesis, we examined TRPV1 (transient receptor potential vanilloid 1)-induced cardiovascular responses in vivo and muscle afferent discharge ex vivo in T2D rats. Additionally, TRPV1 and PKC (protein kinase C) protein levels in dorsal root ganglia subserving skeletal muscle were assessed. For 14 to 16 weeks, Sprague-Dawley rats were given either a normal diet (control) or a high-fat diet in combination with a low dose (35 and 25 mg/kg) of streptozotocin (T2D). Administration of capsaicin, TRPV1 agonist, in hindlimb evoked significantly greater increases in mean arterial pressure and renal sympathetic nerve activity in decerebrated T2D than control. In a muscle-nerve preparation, the discharge to capsaicin exposure in group IV afferents isolated from T2D was likewise significantly augmented at a magnitude that was proportional to glucose concentration. Moreover, the discharge to capsaicin was potentiated by acute exposure of group IV afferents to a high-glucose environment. T2D showed significantly increased phospholyrated-TRPV1 and -PKCα levels in dorsal root ganglia neurons as compared with control. These findings suggest that group IV muscle afferents are sensitized by PKC-induced TRPV1 overactivity in early stage T2D with hyperglycemia and, thereby, may contribute to the potentiated circulatory response to TRPV1 activation in the disease.