Tag Archive for: detrusor

Posts

Article of the Week: β3‐adrenoceptor agonists inhibit carbachol‐evoked Ca2+ oscillations in murine detrusor myocytes

Every Week, the Editor-in-Chief selects an Article of the Week from the current issue of BJUI. The abstract is reproduced below and you can click on the button to read the full article, which is freely available to all readers for at least 30 days from the time of this post.

In addition to the article itself, there is an accompanying editorial written by a prominent member of the urological community. This blog is intended to provoke comment and discussion and we invite you to use the comment tools at the bottom of each post to join the conversation.

Finally, the third post under the Article of the Week heading on the homepage will consist of additional material or media. This week we feature a video discussing the paper.

If you only have time to read one article this week, it should be this one.

β3‐adrenoceptor agonists inhibit carbachol‐evoked Ca2+ oscillations in murine detrusor myocytes

 

Caoimhin S. Grifn, Eamonn Bradley, Mark A. Hollywood, Noel G. McHale, Keith D. Thornbury and Gerard P. Sergeant
Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Co Louth, Ireland

 

Abstract

Objective

To test if carbachol (CCh)‐evoked Ca2+ oscillations in freshly isolated murine detrusor myocytes are affected by β3‐adrenoceptor (β‐AR) modulators.

Materials and Methods

Isometric tension recordings were made from strips of murine detrusor, and intracellular Ca2+ measurements were made from isolated detrusor myocytes using confocal microscopy. Transcriptional expression of β‐AR sub‐types in detrusor strips and isolated detrusor myocytes was assessed using reverse transcriptase‐polymerase chain reaction (RT‐PCR) and real‐time quantitative PCR (qPCR). Immunocytochemistry experiments, using a β3‐AR selective antibody, were performed to confirm that β3‐ARs were present on detrusor myocytes.

Results

The RT‐PCR and qPCR experiments showed that β1‐, β2‐ and β3‐AR were expressed in murine detrusor, but that β3‐ARs were the most abundant sub‐type. The selective β3‐AR agonist BRL37344 reduced the amplitude of CCh‐induced contractions of detrusor smooth muscle. These responses were unaffected by addition of the BK channel blocker iberiotoxin. BRL37344 also reduced the amplitude of CCh‐induced Ca2+ oscillations in freshly isolated murine detrusor myocytes. This effect was mimicked by CL316,243, another β3‐AR agonist, and inhibited by the β3‐AR antagonist L748,337, but not by propranolol, an antagonist of β1‐ and β2‐ARs. BRL37344 did not affect caffeine‐evoked Ca2+ transients or L‐type Ca2+ current in isolated detrusor myocytes.

Conclusion

Inhibition of cholinergic‐mediated contractions of the detrusor by β3‐AR agonists was associated with a reduction in Ca2+ oscillations in detrusor myocytes.

 

Editorial: β3‐adrenoceptor agonists inhibit calcium oscillations in bladder detrusor

The β3‐adrenoceptor (β3‐AR) agonist mirabegron has now been used clinically for the treatment for overactive bladder (OAB) for 5 years, but it is still not clear either exactly where the β3‐ARs are located within the bladder wall or entirely how they work. β3‐AR agonists can reduce detrusor contractions after cholinergic stimulation, but the concentrations of mirabegron required for this effect suggest that this is unlikely to be the main therapeutic route, which may instead involve an indirect pathway or a combination of pathways.

In this issue of BJUI, Griffin et al. 1 show that β3‐AR agonists can reduce the rise in calcium and calcium waves observed after muscarinic receptor activation with carbachol in murine detrusor smooth muscle. They convincingly demonstrate that this effect is mediated by β3‐AR rather than by β1‐AR or β2‐AR and is not mediated by an effect on L‐type calcium channels or depletion of calcium stores; however, although they use BRL37344 and CL316,243, which have a higher potency in rodents than mirabegron, the concentrations of these agents needed are in the micromolar range, significantly higher than the values of ~100 nM measured in plasma following therapeutic dosing with mirabegron 2. It will be interesting to see when these experiments are repeated with, these effects on calcium are also seen in the therapeutic dosing range.

Currently, the only effects of mirabegron reported in the therapeutic dosing range are a reduction in detrusor contractions when elicited by field stimulation and a reduction in acetylcholine release from detrusor strips 34. The similarly of the concentrations required for these two effects have led to the suggestion that the reduction in contractions may be mediated by the reduction in acetylcholine release; however, there is still disagreement as to whether β3‐ARs are located in the cholinergic nerve terminals or not, as different groups have obtained different patterns of β3‐adrenoreceptor staining, even when using the same antibodies 46. It is therefore still unclear if this involves a direct inhibition of acetylcholine release or not, although a predominantly neural source of acetylcholine is indicated by sensitivity to the sodium channel blocker, tetrodotoxin 3.

There is evidence that the reduction may be at least partially mediated via adenosine, such that increased adenosine formed post‐junctionally from breakdown of cAMP following β3‐AR stimulation, acts as a retrograde transmitter to inhibit acetylcholine release by acting at pre‐junctional A1 receptors 4. In support of this, Silva et al. 4 showed that A1 antagonists can reverse the increase in voiding seen with isoprenaline in an anaesthetized rat cystoscopy model.

The reduction in calcium rise reported by Griffin et al. 1 also suggests a post‐junctional site of action and the likely possibility that multiple pathways are activated following the binding of the β3‐AR agonists to post‐junctional receptors. A multiple pronged mechanism may be one of the reasons why mirabegron is successful at reducing the symptoms of OAB whilst sparing normal voiding.

The potency of β3‐AR agonists shows differences depending on the method of stimulation of the muscle, with higher potency seen for inhibition of contraction induced by field stimulation than carbachol stimulation, for example 134. This may reflect differences in the combinations of pathways and receptors activated, with carbachol stimulating only the muscarinic receptors themselves, but field stimulation activating more widely. It would therefore be interesting to see whether the potency of mirabegron to affect calcium release in human tissue is higher when field stimulation is used rather than carbachol, and hence help to evaluate if this pathway is involved in the mechanism of action of mirabegron in the clinic.

L. M. McLatchie
Department of Urology, Guys Hospital, London, UK

 

References
  • Griffin CS, Bradley E, Hollywood MA, McHale NG, Thornbury KD, Sergeant GP. B3‐adrenoceptor agonists inhibit carbachol‐evoked Ca2+ oscillations in murine detrussor myocytesBJU Int 2018121: 959–70

 

  • Krauwinkel W, van Dijk J, Schaddelee M et al. Pharmacokinetic properties of mirabegron, a beta(3)‐adrenoceptor agonist: results from two phase I, randomized, multiple‐dose studies in healthy young and elderly men and womenClin Ther 201234: 2144–60

 

  • D’Agostino G, Condino AM, Calvi P. Involvement of beta(3)‐adrenoceptors in the inhibitory control of cholinergic activity in human bladder: direct evidence by H‐3‐acetylcholine release experiments in the isolated detrusorEur J Pharmacol 2015758: 115–22

 

  • Silva I, Costa AF, Moreira S et al. Inhibition of cholinergic neurotransmission by beta(3)‐adrenoceptors depends on adenosine release and A(1)‐receptor activation in human and rat urinaryAm J Physiol‐Renal Physiol 2017313: F388–403

 

  • Coelho A, Antunes‐Lopes T, Gillespie J, Cruz F. Beta‐3 adrenergic receptor is expressed in acetylcholine‐containing nerve fibers of the human urinary bladder: an immunohistochemical studyNeurourol Urodyn 201736: 1972–80

 

  • Limberg BJ, Andersson KE, Kullmann FA, Burmer G, de Groat WC, Rosenbaum JS. beta‐Adrenergic receptor subtype expression in myocyte and non‐myocyte cells in human female bladderCell Tissue Res 2010342: 295–306

 

Video: β3‐adrenoceptor agonists inhibit carbachol‐evoked Ca2+ oscillations in murine detrusor myocytes

β3‐adrenoceptor agonists inhibit carbachol‐evoked Ca2+ oscillations in murine detrusor myocytes

 

Abstract

Objective

To test if carbachol (CCh)‐evoked Ca2+ oscillations in freshly isolated murine detrusor myocytes are affected by β3‐adrenoceptor (β‐AR) modulators.

Materials and Methods

Isometric tension recordings were made from strips of murine detrusor, and intracellular Ca2+ measurements were made from isolated detrusor myocytes using confocal microscopy. Transcriptional expression of β‐AR sub‐types in detrusor strips and isolated detrusor myocytes was assessed using reverse transcriptase‐polymerase chain reaction (RT‐PCR) and real‐time quantitative PCR (qPCR). Immunocytochemistry experiments, using a β3‐AR selective antibody, were performed to confirm that β3‐ARs were present on detrusor myocytes.

Results

The RT‐PCR and qPCR experiments showed that β1‐, β2‐ and β3‐AR were expressed in murine detrusor, but that β3‐ARs were the most abundant sub‐type. The selective β3‐AR agonist BRL37344 reduced the amplitude of CCh‐induced contractions of detrusor smooth muscle. These responses were unaffected by addition of the BK channel blocker iberiotoxin. BRL37344 also reduced the amplitude of CCh‐induced Ca2+ oscillations in freshly isolated murine detrusor myocytes. This effect was mimicked by CL316,243, another β3‐AR agonist, and inhibited by the β3‐AR antagonist L748,337, but not by propranolol, an antagonist of β1‐ and β2‐ARs. BRL37344 did not affect caffeine‐evoked Ca2+ transients or L‐type Ca2+ current in isolated detrusor myocytes.

Conclusion

Inhibition of cholinergic‐mediated contractions of the detrusor by β3‐AR agonists was associated with a reduction in Ca2+ oscillations in detrusor myocytes.

 

© 2019 BJU International. All Rights Reserved.