Do β3-adrenergic receptors play a role in guinea pig detrusor smooth muscle excitability and contractility?

Abstract

In many species, β3-adrenergic receptors (β3-ARs) have been reported to play a primary role in pharmacologically induced detrusor smooth muscle (DSM) relaxation. However, their role in guinea pig DSM remains controversial. The aim of this study was to investigate whether β3-ARs are expressed in guinea pig DSM and to evaluate how BRL37344 and L-755,507, two selective β3-AR agonists, modulate guinea pig DSM excitability and contractility. We used a combined experimental approach including RT-PCR, patch-clamp electrophysiology, and isometric DSM tension recordings. β3-AR mRNA message was detected in freshly isolated guinea pig DSM single cells. BRL37344 but not L-755,507 caused a slight decrease in DSM spontaneous phasic contraction amplitude and frequency in a concentration-dependent manner. In the presence of atropine (1 μM), only the spontaneous phasic contractions frequency was inhibited by BRL37344 at higher concentrations. Both BRL37344 and L-755,507 significantly decreased DSM carbachol-induced phasic and tonic contractions in a concentration-dependent manner. However, only BRL37344 inhibitory effect was partially antagonized by SR59230A (10 μM), a β3-AR antagonist. In the presence of atropine, BRL37344 and L-755,507 had no inhibitory effect on electrical field stimulation-induced contractions. Patch-clamp experiments showed that BRL37344 (100 μM) did not affect the DSM cell resting membrane potential and K(+) conductance. Although β3-ARs are expressed at the mRNA level, they play a minor to no role in guinea pig DSM spontaneous contractility without affecting cell excitability. However, BRL37344 and L-755,507 have pronounced inhibitory effects on guinea pig DSM carbachol-induced contractions. The study outlines important DSM β3-ARs species differences.

Novel role for the transient potential receptor melastatin 4 channel in guinea pig detrusor smooth muscle physiology

“…1747). The dissection of guinea pig DSM, preparation of tissue strips for contractility studies, and isolation of fresh DSM single cells followed the methods previously described by our group (2,23,31,40).…”

“…TRPM4 currents were recorded using two different protocols. The first protocol including the pipette and bath solutions used followed the method described previously (2,7,24,31,33). The only modifications were that we recorded the transient inward cation currents (TICCs) at a holding potential of Ϫ70 mV (corrected for the junction potential), and the currents were analyzed as open channel probability (NP o) before, after the addition of 9-phenanthrol, and after washout of 9-phenanthrol.…”

“…Isometric DSM tension recordings were conducted as previously described (2,23,31). The experimental details are provided in these reports except for the following modifications.…”

Expression and function of KV2-containing channels in human urinary bladder smooth muscle

“…To eliminate the possible interference from non-DSM cell types, we applied single-cell RT-PCR experiments on freshly isolated human DSM cells. This experimental approach allows us to use selectively only the isolated DSM cells while avoiding any contamination from non-DSM cells (1,8,9,20,21,29). DSM cells were characterized by their elongated, spindle shape, with a bright and shiny contour.…”

“…The expression of K V 2.1 and K V 2.2 channels has been shown in rat DSM (8), and the expression of K V 2.1 and electrically silent K V channel subunits has been detected in guinea pig DSM (21). However, it is questionable whether these findings in animal models could be directly translated to humans, since species differences in human and rodent DSM function are well documented (1,3,5,8,17,21,30).Knowledge about K V channels in human DSM is limited and only the molecular expression of some K V 1 channels has been proven (10). There is a lack of information about expression, function, and regulation of each individual K V channel in human DSM.…”