Login to Access Video or Poster Abstract: MP42-10
Sources of Funding: Department of Veterans Affairs, Research Service BX001790; BX002806

Introduction

Diabetic bladder is characterized by an early compensatory phase in which bladder smooth muscle (BSM) exhibits augmented contractility. While little is known about the causes of this response, an upregulation of Rho-dependent signaling in response to hyperglycemia has been suggested. In other smooth muscle systems, RhoA-ROCK signaling has been shown to be dependent on caveolae, membrane invaginations involved in the regulation of a myriad of signaling pathways. Since alterations in caveolar elements have been reported in animal models of diabetes, this study investigated the involvement of these membrane microdomains in the Rho-dependent changes in contractility induced by hyperglycemia.

Methods

Longitudinal mouse bladder strips without mucosa were mounted in organ baths for isometric tension studies. Changes in the amplitude of bladder contractions in response to exogenous carbachol (1μM) were evaluated under euglycemia (11.5mM) as well as after exposure of BSM tissue to high glucose Krebs (23mM) for up to 8 hours. Separate experiments were similarly performed in Krebs supplemented with mannitol (11.5mM) to control for increased osmotic conditions. The effect of high glucose on contractile responses to CCh was investigated in the presence of Rho kinase inhibitor Y27632 (1μM), as well as after the depletion of BSM caveolae, achieved by incubation with mβCD (10mM, 1 hour).

Results

The amplitude of contractile responses to CCh measured in BSM were significantly higher after 2 hours of hyperglycemia compared to those measured under euglycemic conditions and remained elevated for 8 hours. Contractile responses to CCh remained unchanged over the same time period in the presence of mannitol. The augmented CCh responses induced by high glucose were completely prevented in the presence of Rho kinase inhibitor used at a dose that did not affected CCh responses under euglycemia. Similarly, augmented CCh responses induced by hyperglycemia were prevented after BSM caveolae were depleted by exposure to mβCD.

Conclusions

The increased detrusor responses to CCh during exposure to hyperglycemia is consistent with BSM hypercontractility reported in the compensated phase of diabetes. The effects of Rho kinase inhibitor and mβCD in preventing the increase in BSM responsiveness under hyperglycemic conditions suggest the involvement of Rho-mediated pathway and the requirement of intact caveolae in this process. These findings might provide a potential link between the diabetes-induced BSM hyperreactivity and the caveolae-mediated regulation of Rho signaling.

Funding

Department of Veterans Affairs, Research Service BX001790; BX002806