Functional characterization of rat submaxillary gland muscarinic receptorsusing microphysiometry

1 Muscarinic cholinoceptors (MChR) in freshly dispersed rat salivary gland (RSG) cells were characterized using microphysiometry to measure changes in acidification rates. Several non-selective and selective muscarinic antago nists were used to elucidate the nature of the subtypes mediating the respo nse to carbachol. 2 The effects of carbachol (pEC(50) = 5.74 +/- 0.02 s.e.mean; n = 53) were highly reproducible and most antagonists acted in a surmountable, reversibl e fashion. The following antagonist rank order, with apparent affinity cons tants in parentheses, was noted: 4-DAMP (8.9)= atropine (8.9) > tolterodine (8.5) > oxybutynin (7.9) > S-secoverine (7.2) > pirenzepine (6.9) > himbac ine (6.8) > AQ-RA 741 (6.6) > methoctramine (5.9). 3 These studies validate the use of primary isolated RSG cells in microphys iometry for pharmacological analysis. These data are consistent with, and e xtend, previous studies using alternative functional methods, which reporte d a lack of differential receptor pharmacology between bladder and salivary gland tissue. 4 The antagonist affinity profile significantly correlated with the profile at human recombinant muscarinic M-3 and M-5 receptors. Given a lack of ant agonists that discriminate between M-3 and M-5, definitive conclusion of wh ich subtype(s) is present within RSG cells cannot be determined.