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

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

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.

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.

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