Modulation of chloride, potassium and bicarbonate transport by muscarinic receptors in a human adenocarcinoma cell line.
1. Short-circuit current (I(SC)) responses to carbachol (CCh) were investigated in Colony 1 epithelia, a subpopulation of the HCA-7 adenocarcinoma cell line. In Krebs-Henseleit (KH) buffer, CCh responses consisted of three I(SC) components: an unusual rapid decrease (the 10 s spike) followed by an upward spike at 30 s and a slower transient increase (the 2 min peak). This response was not potentiated by forskolin; rather, CCh inhibited cyclic AMP-stimulated I(SC). 2. In HCO3- free buffer, the decrease in forskolin-elevated I(SC) after CCh was reduced, although the interactions between CCh and forskolin remained at best additive rather than synergistic. When Cl- anions were replaced by gluconate, both Ca2+- and cyclic AMP-mediated electrogenic responses were significantly inhibited. 3. Basolateral Ba2+ (1-10 mM) and 293B (10 microM) selectively inhibited forskolin stimulation of I(SC), without altering the effects of CCh. Under Ba2+- or 293B-treated conditions, CCh responses were potentiated by pretreatment with forskolin. 4. Basolateral charybdotoxin (50 nM) significantly increased the size of the 10 s spike of CCh responses in both KH and HCO3- free medium, without affecting the 2 min peak. The enhanced 10 s spike was inhibited by prior addition of 5 mM apical Ba2+. Charybdotoxin did not affect forskolin responses. 5. In epithelial layers prestimulated with forskolin, the muscarinic antagonists atropine and 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP, both at 100 nM) abolished subsequent 10 microM CCh responses. Following addition of p-fluoro hexahydro-sila-difenidol (pF-HHSiD, 10 microM) or pirenzepine (1 microM), qualitative changes in the CCh response time-profile also indicated a rightward shift of the agonist concentration-response curve; however, 1 microM gallamine had no effect. These results suggest that a single M3-like receptor subtype mediates the secretory response to CCh. 6. It is concluded that CCh and forskolin activate discrete populations of basolateral K+ channels gated by either Ca2+ or cyclic AMP, but that the Cl- permeability of the apical membrane may limit their combined effects on electrogenic Cl- secretion. In addition, CCh activates a Ba2+-sensitive apical K+ conductance leading to electrogenic K+ transport. Both agents may also modulate HCO3- secretion through a mechanism at least partially dependent on carbonic anhydrase.
Division of Pharmacology & Therapeutics, GKT, St. Thomas's Medical School, London.
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D000086:Acetazolamide / Q000494:pharmacology; D000230:Adenocarcinoma; D001464:Barium / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000187:drug effects / Q000502:physiology; D016764:Cell Polarity; D018999:Charybdotoxin / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism / Q000494:pharmacology; D002839:Chromans / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D003470:Culture Media / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D006801:Humans; D007287:Inorganic Chemicals / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D002712:Chlorides; D002839:Chromans; D003470:Culture Media; D004232:Diuretics; D007287:Inorganic Chemicals; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D026902:Potassium Channel Blockers; D011976:Receptors, Muscarinic; D013449:Sulfonamides; D018999:Charybdotoxin; C103474:6-cyano-4-(N-ethylsulfonyl-N-methylamino)-3-hydroxy-2,2-dimethylchromane; D005576:Colforsin; D001464:Barium; D002217:Carbachol; C015451:piretanide; D002256:Carbonic Anhydrases; D000086:Acetazolamide; D011188:Potassium