Cholinergic Stimulation of Salivary Secretion Studied with M₁ and M₃ Muscarinic Receptor Single- and Double-Knockout Mice

Abstract

Identification of the specific muscarinic acetylcholine receptor (mAChR) subtypes mediating stimulation of salivary secretion is of considerable clinical interest. Recent pharmacological and molecular genetic studies have yielded somewhat confusing and partially contradictory results regarding the involvement of individual mAChRs in this activity. In the present study, we re-examined the roles of M 1 and M 3 mAChRs in muscarinic agonist-mediated stimulation of salivary secretion by using M 1 and M 3 receptor single-knockout (KO) mice and newly generated M 1 /M 3 receptor double-KO mice. When applied at a low dose (1 mg/kg, s.c.), the muscarinic agonist pilocarpine showed significantly reduced secretory activity in both M 1 and M 3 receptor single-KO mice. However, when applied at higher doses, pilocarpine induced only modestly reduced (5 mg/kg, s.c.) or unchanged (15 mg/kg, s.c.) salivation responses, respectively, in M 1 and M 3 receptor single-KO mice, indicating that the presence of either M 1 or M 3 receptors is sufficient to mediate robust salivary output. Quantitative reverse transcriptase-polymerase chain reaction studies with salivary gland tissue showed that the inactivation of the M 1 or M 3 mAChR genes did not lead to significantly altered mRNA levels of the remaining mAChR subtypes. Strikingly, the sialagogue activity of pilocarpine was abolished in M 1 /M 3 receptor double-KO mice. However, salivary glands from M 1 /M 3 receptor double-KO mice remained responsive to stimulation by the ␤-adrenergic receptor agonist, (S)-isoproterenol. Taken together these studies support the concept that a mixture of M 1 and M 3 receptors mediates cholinergic stimulation of salivary flow.

Impairment of TRPC1–STIM1 channel assembly and AQP5 translocation compromise agonist-stimulated fluid secretion in mice lacking caveolin1

“…These water channels are retained in close proximity to the apical membrane and undergo an increase in surface expression in response to the elevation of [Ca 2+ ] i following receptor activation (Gresz et al, 2004;Ishikawa et al, 2005). Interestingly, mouse models with deletion in key molecular components involved in regulation of [Ca 2+ ] i , such as the M3 muscarinic receptor or the inositol (1,4,5)-trisphosphate receptors IP 3 R2 and IP 3 R3, display severe loss in pilocarpine (a muscarinic receptor agonist) stimulated saliva secretion (Futatsugi et al, 2005;Gautam et al, 2004;Matsui et al, 2000). The transient receptor potential canonical 1 (TRPC1) channel and Orai1 have been shown to contribute for agonist-stimulated Ca 2+ influx in salivary and pancreatic acinar cells, respectively (Hong et al, 2011;Liu et al, 2007;Ong et al, 2007;Singh et al, 2001).…”

Distinct mixtures of muscarinic receptor subtypes mediate inhibition of noradrenaline release in different mouse peripheral tissues, as studied with receptor knockout mice

“…However, all studies that have addressed this issue so far suggest that such changes are unlikely to occur (Gautam et al, 2004;Wess, 2004). Moreover, we cannot completely rule out the possibility that formation of muscarinic heterodimers (Novi et al, 2005) may have affected the outcome of the functional studies.…”

Transdermal delivery of tolterodine tartrate for overactive bladder treatment: In vitro and in vivo evaluation

“…This shows that oral TT markedly suppresses pilocarpine-stimulated salivation. Salivary secretion studies indicated higher activity of oral TT in the salivary gland than the transdermal matrix patch containing TT (10). A decrease was observed in the total amount of saliva collected in the second hour aft er patch administration, demonstrating that transdermal TT exerted a lesser eff ect on salivary glands than oral administration.…”

“…Upon administration, TT is metabolized by the liver (Cytochrome P450 2D6) to pharmacologically active 5-hydroxy-methyl derivative (7,8). The drug has in vivo functional selectivity for muscarinic receptors in the bladder over the salivary glands and hence it is suitable for the treatment of OAB (9,10). Transdermal delivery allows superior control of systemic drug concentration, by-passes fi rst pass metabolism, minimizes gastrointestinal side eff ects, allows immediate termination of administration in case of toxicity and greatly improves patient compliance (11)(12)(13).…”