Colonic Hypersensitivity and Sensitization of Voltage-gated Sodium Channels in Primary Sensory Neurons in Rats with Diabetes

Abstract

Background/AimsPatients with long-standing diabetes often demonstrate intestinal dysfunction and abdominal pain. However, the pathophysiology of abdominal pain in diabetic patients remains elusive. The purpose of study was to determine roles of voltage-gated sodium channels in dorsal root ganglion (DRG) in colonic hypersensitivity of rats with diabetes. MethodsDiabetic models were induced by a single intraperitoneal injection of streptozotocin (STZ; 65 mg/kg) in adult female rats, while the control rats received citrate buffer only. Behavioral responses to colorectal distention were used to determine colonic sensitivity in rats. Colon projection DRG neurons labeled with DiI were acutely dissociated for measuring excitability and sodium channel currents by whole-cell patch clamp recordings. Western blot analysis was employed to measure the expression of Na V 1.7 and Na V 1.8 of colon DRGs. ResultsSTZ injection produced a significantly lower distention threshold than control rats in responding to colorectal distention. STZ injection also depolarized the resting membrane potentials, hyperpolarized action potential threshold, decreased rheobase and increased frequency of action potentials evoked by 2 and 3 times rheobase and ramp current stimulation. Furthermore, STZ injection enhanced neuronal sodium current densities of DRG neurons innervating the colon. STZ injection also led to a significant upregulation of Na V 1.7 and Na V 1.8 expression in colon DRGs compared with age and sex-matched control rats. ConclusionsOur results suggest that enhanced neuronal excitability following STZ injection, which may be mediated by upregulation of Na V 1.7 and Na V 1.8 expression in DRGs, may play an important role in colonic hypersensitivity in rats with diabetes.

α-lipoic acid suppresses neuronal excitability and attenuates colonic hypersensitivity to colorectal distention in diabetic rats

“…Three weeks after STZ injection, ALA at 60 mg/kg or NS in the same volume was injected (IP) once a day for consecutive 7 days. T13-L2 DRGs were dissociated acutely, and small and medium-sized DRG neurons in red were recorded (Figure 2B, arrow), as we have shown in a previous study 15. ALA treatment significantly reduced excitability of colonic DRG neurons, compared with NS.…”

“…It was reported that STZ injection led to gastric and colonic hypersensitivity,25,36 in addition to peripheral sensorimotor neuropathy in rats 24,37. Recently, we have reported that diabetic rats display colonic visceral hypersensitivity in response to CRD 15. In the present study, we provided direct evidence for the first time to demonstrate that systematical application of ALA significantly attenuated the colonic visceral hypersensitivity in rats with diabetes.…”

“…Expressions of NaV1.7 and NaV1.8 in colonic DRGs (T13-L2 DRGs) from diabetic and CON rats were determined using western blotting analysis, as previously described in detail 15. The primary antibodies used to probe the target proteins included rabbit anti-NaV1.7 or anti-NaV1.8 (1:200, Alomone Labs, Jerusalem, Israel), rabbit anti-GAPDH (1:1000, Biotechnology Co., CHN), and mouse anti-actin (1:1000; Chemicon, Temecula, CA, USA).…”

“…Diabetic colonic hypersensitivity has been reported to be associated with the depressed Kv4.2 expression and function in primary sensory neurons innervating the colon 14. Our previous study has shown that diabetic rats, induced by streptozotocin (STZ), showed a significant colonic hypersensitivity, which is likely mediated by enhanced function and expression of voltage-gated sodium channel (VGSC) NaV1.7 and NaV1.8 subunits in dorsal root ganglion (DRG) neurons 15. These data strongly indicate that ion channels in the primary sensory neurons play a pivotal role in the development of colonic visceral hypersensitivity.…”

Acute Effects of Transforming Growth Factor-β1 on Neuronal Excitability and Involvement in the Pain of Rats with Chronic Pancreatitis

“…3,4,22 In brief, bilateral T9-T13 DRGs were dissected out and incubated in dissecting solution containing collagenase D (1.5-1.8 mg/mL; Roche, Indianapolis, IN, USA) and trypsin (1.2 mg/mL; Sigma-Aldrich) for 90 minutes at 34.5°C. DRGs were then washed and transferred to the dissecting solution containing DNase (0.5 mg/mL; Sigma-Aldrich).…”