Content and contractile effect of arginine vasopressin in rat urinary bladder

Effects of vasopressin receptor agonists on detrusor smooth muscle tone in young and aged bladders: Implications for nocturia treatment

PURPOSE

The main goal of this study was to determine the effects of arginine vasopressin (AVP) and desmopressin on bladder contractility and to examine whether the effects of these vasopressin receptor (VR) agonists differ in young versus aged animals. These aims were addressed using urinary bladders from young (3 months) and aged (24 month) female Fischer 344 rats that were isolated and dissected into strips for isometric tension recordings. Bladder strips were exposed to AVP and desmopressin through the perfusate, and tension changes recorded.

RESULTS

In young rat bladders, AVP, an agonist at both vasopressin-1 receptors (V₁Rs) and vasopressin-2 receptor (V₂Rs), concentration-dependently caused contraction of bladder strips with a sensitivity that was greater in young versus aged bladder strips. Removal of the mucosa did not alter the sensitivity of young bladder strips to AVP yet enhanced the AVP sensitivity of aged bladder strips. The differential sensitivity to AVP between young denuded and aged denuded bladder strips was similar. In contrast to AVP, desmopressin (V₂R selective agonist) relaxed bladder strips. This response was reduced by removal of the mucosa in young, but not aged, bladder strips.

CONCLUSION

These findings support a direct role for VRs in regulating detrusor tone with V₁Rs causing contraction and V₂Rs relaxation. In aged bladders, the contractile response to V₁R activation is attenuated due to release of a mucosal factor that attenuates V₁R-induced contractions. Also in aged bladders, the relaxation response to V₂R activation is attenuated by lack of release of a mucosal factor that contributes to V₂R-induced relaxation. Thus age-associated changes in the bladder mucosa impair the effects of VRs on bladder tone. Because the V₂R signaling system is impaired in the older bladder, administering an exogenous V₂R agonist (e.g., desmopressin) could counteract this defect. Thus, desmopressin could potentially increase nighttime bladder capacity through detrusor relaxation in concert with decreased urine production, reducing nocturnal voiding frequency.

Single-Cell Transcriptomic Map of the Human and Mouse Bladders

BACKGROUND

Having a comprehensive map of the cellular anatomy of the normal human bladder is vital to understanding the cellular origins of benign bladder disease and bladder cancer.

METHODS

We used single-cell RNA sequencing (scRNA-seq) of 12,423 cells from healthy human bladder tissue samples taken from patients with bladder cancer and 12,884 cells from mouse bladders to classify bladder cell types and their underlying functions.

RESULTS

We created a single-cell transcriptomic map of human and mouse bladders, including 16 clusters of human bladder cells and 15 clusters of mouse bladder cells. The homology and heterogeneity of human and mouse bladder cell types were compared and both conservative and heterogeneous aspects of human and mouse bladder evolution were identified. We also discovered two novel types of human bladder cells. One type is ADRA2A ⁺ and HRH2 ⁺ interstitial cells which may be associated with nerve conduction and allergic reactions. The other type is TNNT1 ⁺ epithelial cells that may be involved with bladder emptying. We verify these TNNT1 ⁺ epithelial cells also occur in rat and mouse bladders.

CONCLUSIONS

This transcriptomic map provides a resource for studying bladder cell types, specific cell markers, signaling receptors, and genes that will help us to learn more about the relationship between bladder cell types and diseases.

Non-uniform changes in membrane receptors in the rat urinary bladder following outlet obstruction

The aim of the present study was to investigate the expression and distribution of membrane receptors after bladder outlet obstruction (BOO). Partial bladder outlet obstruction (BOO) was induced in female rats and bladders were harvested after either 10 days or 6 weeks of BOO. The expression of different receptors was surveyed by microarrays and corroborated by immunohistochemistry and western blotting. A microarray experiment identified 10 membrane receptors that were differentially expressed compared to sham-operated rats including both upregulated and downregulated receptors. Four of these were selected for functional experiments on the basis of magnitude of change and relevance to bladder physiology. At 6 weeks of BOO, maximal contraction was reduced for neuromedin B and vasopressin (AVP), consistent with reductions of receptor mRNA levels. Glycine receptor-induced contraction on the other hand was increased and receptor mRNA expression was accordingly upregulated. Maximal relaxation by the β3-adrenergic receptor agonist CL316243 was reduced as was the receptor mRNA level. Immunohistochemistry supported reduced expression of neuromedin B receptors, V1a receptors and β3-adrenergic receptors, but glycine receptor expression appeared unchanged. Western blotting confirmed repression of V1a receptors and induction of glycine receptors in BOO. mRNA for vasopressin was detectable in the bladder, suggesting local AVP production. We conclude that changes in receptor expression following bladder outlet obstruction are non-uniform. Some receptors are upregulated, conferring increased responsiveness to agonist, whereas others are downregulated, leading to decreased agonist-induced responses. This study might help to select pharmacological agents that are effective in modulating lower urinary tract symptoms in BOO.

Vasopressin-induced mouse urethral contraction is modulated by caveolin-1

Caveolae are 50-100nm large invaginations in the cell membrane that are considered to play roles in receptor signaling. Here we aimed to investigate the expression and distribution of the arginine-vasopressin (AVP) V1a receptor and its functional dependence on caveolin-1 (Cav1) in the mouse urethra. Female Cav1 knockout (KO) and wild type (WT) mice were used, and urethral preparations were micro-dissected for mechanical experiments. Methyl-β-cyclodextrin (mβcd) was used to deplete cholesterol and to disrupt caveolae. Protein expression and localization was determined using immunofluorescence and western blotting and transcript expression was determined by qRT-PCR. We found that Cav1 and AVP V1a receptors were expressed in urethral smooth muscle cells with apparent co-localization at the cell membrane. AVP caused urethral contraction that was inhibited by the V1a receptor antagonist SR49059. Concentration-response curves for AVP were right-shifted and maximal contraction was reduced in Cav1 KO mice and after mβcd treatment. In addition to caveolin-1 we also detected caveolin-2, cavin-1 and cavin-3 in the mouse urethra by western blotting. Caveolin-2, cavin-1 and cavin-3 as well as V1a receptor expression was reduced in KO urethra. We conclude that AVP regulates urethral contractility via the V1a receptor through a Cav1-dependent mechanism involving, in part, altered V1a receptor expression.

Effect and content of arginine vasopressin in normal and obstructed rat urinary bladder: an in vivo and in vitro investigation

The present investigation was performed to evaluate the possible role of arginine vasopressin (AVP) in detrusor instability in the obstructed rat urinary bladder. The effect of AVP on normal and obstructed rat detrusor smooth muscle was tested in vivo and in vitro. Arginine vasopressin given as a closed intraarterial injection to the bladder transiently decreased micturition volume and increased micturition frequency during cystometry in control rats. In rats with infravesical outlet obstruction the effect of AVP on cystometrical parameters was negligible. In accordance with this finding, the efficacy of AVP in contracting detrusor muscle in vitro was much lower for obstructed bladders than for controls. The EC50 values were, however, similar. Arginine vasopressin added to the bath had no effect on nerve-mediated contractile responses. Obstruction led to a transient decrease in immunoreactive AVP concentration, but the total amount of AVP per bladder increased significantly after 6 weeks of obstruction as a consequence of the 14-fold increase in bladder weight. The decreased excitatory effect of AVP in obstructed bladder makes a role for this peptide in the development of detrusor instability less likely.

Contractile effect and tissue content of arginine vasopressin in the urinary bladder of Brattleboro rats with hereditary diabetes insipidus

1. Urinary bladders from male rats of the Brattleboro strain with hereditary diabetes insipidus (DI) were analyzed for presence of immunoreactive arginine vasopressin (ir-AVP). Healthy rats were used as controls. 2. Bladders from the DI rats were heavier than controls. Concentration of ir-AVP was lower in DI bladders, but total amount of ir-AVP was similar to that in controls. 3. EC50 values for the AVP concentration-response relations were similar for control and DI bladder strips. Maximum response to AVP relative to response to K+ high solution was lower in the DI group. 4. An AVP receptor antagonist that significantly blocked response to exogenous AVP had no effect on response to field stimulation. 5. We suggest that AVP is synthetized locally and that AVP is not the non-adrenergic non-cholinergic transmitter responsible for the atropine resistant contraction in rat bladder.

Arginine-vasopressin induces mode-2 gating in L-type Ca2+ channels (smooth muscle cells of the urinary bladder of the guinea-pig)

The effect of arginine-vasopressin (AVP, 0.1 microM) on elementary Ca2+ channel currents (L-type) was studied in cell-attached patches with 10 mM BaCl2 as the charge carrier. At a constant potential of -30 mV, bath applied AVP increased the channel openness (NPo) by a factor of 4.7 +/- 3.0 (mean +/- SD, n = 9), the effect resulted from an increase in the frequency of opening (factor 2.5 +/- 0.8) and from a longer mean open time. Under control, openings longer than 5 ms contributed only 4% of the total, however, with the application of AVP this contribution increased to 29%. Under control, the open times were distributed along a single exponential (tau o1 = 0.8 +/- 0.4 ms), a double exponential distribution was obtained during AVP (tau o1 = 0.8 +/- 0.5 ms, tau o2 = 7.5 +/- 0.7 ms). The Ca2+ agonist BAYk8644 (1 microM) changed the open time distribution similarly to AVP (tau o1 = 1.0 +/- 0.5 ms, tau o2 = 9 +/- 2.8 ms). With 1 microM BAYk8644 in the bath, AVP did not significantly increase the relative contribution of long openings, however, AVP increased the frequency of openings by a factor of 2.0 +/- 1 (n = 6). The results are compatible with the idea that AVP can change the gating of L-type Ca2+ channels from mode 1 to mode 2.