Expression of TRPM8 in diabetic rats and its relationship with visceral pain stimulation

Transient receptor potential cation channel, subfamily M, member 8 (TRPM8) is a nonselective cation channel and a candidate for cold sensation signaling, but the relationship between TRPM8 and diabetes remains unclear. In the present study, we determined the expression levels of TRPM8 messenger RNA (mRNA) and the levels of the TRPM8 protein in the bladder tissue of diabetic rats. We also investigated the correlation between TRPM8 expression and the visceral pain stimulation-related factor, calcitonin gene-related peptide (CGRP) in diabetic rats. The rats were sacrificed 3, 5, 7, and 15 days after streptozotocin injection, and blood was collected from their tail veins to determine the blood glucose levels. Bladder tissue was removed to assess the expression of TRPM8 mRNA by reverse transcription-polymerase chain reaction, and the expression of the TRPM8 protein by western blotting. After administering electrical stimulation (5 V/1 Hz), the expression levels of TRPM8 and CGRP proteins were determined. Our results revealed that the blood glucose level, and TRPM8 mRNA and TRPM8 protein expression levels increased significantly in the diabetic rats. Spinal tissue protein expression levels of both TRPM8 and CGRP also increased significantly following electrical stimulation. This possibly indicates that TRPM8 is closely associated with visceral pain stimulation, and could be an independent prognostic biomarker for diabetes.