Evidence for muscarinic 3 receptor mediated ion transport in HT29 cells studied by X-ray microanalysis

Changes in elemental content in response to muscarinic drugs in HT29 cells were investigated by X-ray microanalysis. Acetylcholine (ACh) and carbachol (Cch), both agonists binding to muscarinic receptors, induced a decrease of the intracellular Cl and K content. This agrees with the notion that these agonists induce electrolyte and water secretion. Atropine, a non-selective antagonist of muscarinic receptors, inhibited the decrease in K and Cl caused by ACh and Cch, and instead caused an increase of the Cl and K concentrations. A similar inhibition was found in the case of the selective muscarinic 3 receptor antagonist P-F-HHSiD. In contrast, the selective muscarinic 2 receptor antagonist AF-DX 116 did not inhibit Cch-activated secretion of K and Cl. A slight inhibition of ACh induced ion secretion was seen, but this inhibition was weak compared to that caused by P-F-HHSiD. Treatment with U-73122, an inhibitor of phospholipase C, blocked ACh or Cch induced ion secretion. These results suggest that ACh and Cch stimulated secretion of Cl and K is mediated by muscarinic 3 receptors via the inositol-1,4,5-trisphosphate (IP3) dependent pathway.