Muscarinic stimulation of gallbladder epithelium. I. Electrophysiology and signaling mechanisms.
To understand the effects of acetylcholine (ACh) on fluid-absorbing epithelia, we carried out experiments on Necturus gallbladder epithelium. Binding studies with 1-quinuclidinyl[phenyl-4(N)-3H]benzilate (QNB) demonstrated that Necturus gallbladder epithelial cells express high-affinity muscarinic receptors. The effects of ACh and carbachol were exerted from the basolateral surface and consisted of a transient hyperpolarization of both cell membranes and a concomitant decrease in the apparent fractional resistance of the apical membrane. Atropine blocked both effects. ACh also elicited transient elevations of inositol 1,4,5-trisphosphate and intracellular free calcium ([Ca2+]i) levels, the latter by both release from intracellular stores and basolateral influx. The phospholipase C antagonist U-73122 inhibited the effects of ACh, whereas inhibition of prostaglandin and guanosine 3',5'-cyclic monophosphate synthesis with indomethacin or methylene blue, respectively, had no effect. In conclusion, Necturus gallbladder epithelium expresses muscarinic receptors in the basolateral membrane. Receptor activation stimulates phospholipase C and elevates cellular levels of inositol 1,4,5-trisphosphate and [Ca2+]i. The elevation in [Ca2+]i activates K+ channels but apparently not Cl- channels.
Altenberg
G A
GA
Department of Physiology, University of Texas Medical Branch, Galveston 77555.
Subramanyam
M
M
Bergmann
J S
JS
Johnson
K M
KM
Reuss
L
L
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004594:Electrophysiology / Q000379:methods; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D004963:Estrenes / Q000494:pharmacology; D005704:Gallbladder / Q000502:physiology*; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008751:Methylene Blue / Q000494:pharmacology; D009337:Necturus; D011760:Pyrrolidinones / Q000494:pharmacology; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D004963:Estrenes; D011760:Pyrrolidinones; D011976:Receptors, Muscarinic; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D011813:Quinuclidinyl Benzilate; D001285:Atropine; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D010738:Type C Phospholipases; D000109:Acetylcholine; D002118:Calcium; D008751:Methylene Blue; D007213:Indomethacin