Reduction of Urinary Bladder Activity in Transgenic Sickle Cell Disease Mice.

Abstract 2580

Poster Board II-557

Genitourinary infection and urinary retention have been related to impaired urinary concentrating ability and altered urinary volume in sickle cell disease (SCD) patients. This condition may be associated with changes in the detrusor smooth muscle (DSM) reactivity. Berkeley transgenic SCD mice display several clinical manifestations similar to those seen in humans, but no studies assessing the alterations of DSM reactivity in SCD mice have been performed. DSM contractions are a consequence of the activation of muscarinic receptors that promote stimulation of phospholipase C, with increased formation of inositol trisphosphate and diacylglycerol to release calcium (Ca²⁺) from intracellular stores, leading to bladder emptying. The Ca²⁺-independent RhoA/Rho-kinase pathway is also involved in the regulation of bladder smooth muscle tone by alteration of the sensitivity of contractile proteins for Ca²⁺. Changes in the contraction mechanisms of DSM may contribute to bladder dysfunction. The aim of this study was to evaluate the contractile mechanisms of isolated DSM of transgenic SCD mouse. SCD (SS) and C57BL/6 (CTL) mice tissues were removed and mounted in 10ml organ baths containing Krebs solution at 37°C and continuously bubbled with a mixture of 95%O₂:5%CO₂ (pH 7.4). Tissues were stretched to a resting tension of 10 mN and allowed to equilibrate for 60 minutes. Changes in isometric force were recorded using a PowerLab400 Data Acquisition System. Cumulative concentration-response curves to muscarinic agonist carbachol (CCh; 0.01–100 μM) were obtained in the absence and presence of the Rho-kinase inhibitor Y-27632 (1–10 μM). Cumulative concentration-response curves were constructed to hyperpolarizing solution, potassium chloride (KCl; 1–300 mM) and calcium chloride (CaCl₂; 0.01–100 mM). Frequency-response curves for electrical field stimulation (EFS; 1–32 Hz) were obtained in strips in the absence and presence of non-selective muscarinic antagonist atropine (1 μM) or purinergic receptor antagonist suramin (100 μM). Cumulative addition of the CCh produced concentration-dependent contractile responses in DSM, although the potency (pEC₅₀) did not change in SS mice (5.80±0.02) compared with CTL mice (5.69±0.05). In contrast, the maximal response (E_max) was significantly reduced in SS mice (4.20±0.42mN) compared with CTL mice (9.96±1.77mN). In addition, the pEC₅₀ and E_max elicited by CCh were reduced in the presence of Y-27632; however, no change was observed among all group studies. Cumulative addition of the KCl produced concentration-dependent contraction in DSM, and both pEC₅₀ (0.98±0.08) and E_max (7.63±1.03mN) were significantly reduced in SS mice, compared with CTL mice (1.24±0.07; 11.24±0.84mN, respectively). CaCl₂ produced concentration-dependent contractile responses, the pEC₅₀ did not change in SS mice (2.00±0.06); however, the E_max was significantly reduced (10.1±0.25mN) when compared to CTL mice (1.92±0.05; 17.8±2.3mN). EFS-induced contractions in DSM of SS mice were decreased at significantly higher frequencies than compared to CTL mice. In addition, EFS-induced contractions in DSM were significantly decreased in the presence of atropine and suramin in both SS mice and CTL mice, but no change was observed among all group studies. Our study shows that SS mice exhibit impaired contractile responses to muscarinic agonist, KCl, CaCl₂ and EFS, with no involvement of the Rho-kinase signaling pathway. This bladder dysfunction may contribute to the increased risk of urinary tract infections observed in SCD patients. Further studies are necessary to better understand the relationship between DSM reactivity alterations and genitourinary manifestations in SCD.