Our previous study has demonstrated the important role of chloride channels on the regulation of urinary bladder smooth muscle tone. We investigated the differences in functional expressions of calcium-activated chloride channels (CaCCs) on bladder smooth muscle (SM) among normal, and metabolic syndrome (Mets) induced overactive bladder (OAB) and underactive bladder (UAB) rats.

Fructose feeding rats (FFRs) were fed a fructose rich diet while control animals received standard rat chow for 6 months. After collecting the urine samples for measurement of urinary nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), continuous infusion cystometry (CMG) was performed. Then the bladder SM tissues were harvested for protein and mRNA expressions of CLCA4 and ANO1 chloride channels using western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR). Based on the results of CMG at month 6, FFRs were categorized into NDF (normal detrusor function), OAB and UAB groups. The CMG parameters, urine NGF and BDNF levels, molecular expressions of CaCCs were compared among rats in control, NDF, OAB and UAB groups.

The body weight, bladder weight, serum glucose, insulin levels and insulin resistance increased significantly in FFR rats, proving the status of Mets. Among them, the serum glucose level and insulin resistance increased most in UAB group (Fig 1). When compared with control group, both urine NGF and BDNF levels increased significantly in OAB and UAB groups. However, the increases were significantly higher in OAB than in UAB groups. Western blot analysis showed significantly increased expressions of CLCA4 and ANO1 proteins on rat bladder SM in OAB and UAB groups (Fig 2). Also, the increases were significantly higher in OAB than in UAB groups. Quantitative RT-PCR analysis demonstrated significantly increased expressions of the mRNA for CLCA4 and ANO1 in OAB and UAB groups. There was no significant change of urine NGF, BDNF levels, or molecular expressions of CaCCs on bladder SM in NDF group.

The changes of body weight, bladder weight, serum glucose, insulin levels and insulin resistance showed the effectiveness of FFR on induction of Mets in rats. The significant increase of serum glucose level and the highest increase of insulin resistance in UAB group indicated UAB group may represent the most severe condition of Mets. In OAB group, the urine NGF and BDNF levels were highest among all groups, while in UAB group, the levels were lower than OAB but still higher than control group. Meanwhile, the changes of expressions in CLCA4 and ANO1 chloride channel proteins and mRNA were parallel to those of urine NGF and BDNF levels, demonstrating the role of CaCCs on evolution of different stages of bladder pathology caused by Mets.

The UAB group may represent the most severe condition of Mets. The changes of urine NGF and BDNF levels, and the expressions of CLCA4 and ANO1 chloride channel proteins and mRNA on rat bladder SM in OAB and UAB groups may reflect the role of CaCCs on evolution of different stages of bladder pathology caused by Mets.