Muscarinic response in rat lacrimal glands.
A large variety of responses has been uncovered by recent investigations of conductance changes elicited by muscarinic agonists. In exocrine glands, the permeability to K+, Cl- and Na+ ions is increased, and internal Ca2+ serves as a second messenger. Patch-clamp analysis of the secreting cells has revealed three types of Ca2+-dependent channels, which are respectively selective for K+, for Cl-, and for monovalent cations. The channels differ in their sensitivity to the internal Ca2+ concentration, Cai. K+-selective channels are partially activated at rest, with Cai approx. 10 nmol l-1; Cl(-)-selective channels are activated between 100 nmol l-1 and 1 mumol l-1; activation of cationic channels requires micromolar Cai levels. Cell-attached recordings, performed either on isolated cells or on cell clusters, show an activation of all three channel types upon application of acetylcholine. In whole-cell recordings, mostly K+- and Cl(-)-selective channels are activated. The cell currents display slow oscillations linked to variations of Cai. Whole-cell currents rise after a delay of approx. 1 s, and decay with a time constant of approx. 0.7 s upon removal of acetylcholine. They do not depend on extracellular Ca2+. The recent demonstration that Ca2+-dependent currents can also be obtained when dialysing the cells with inositoltrisphosphate or with GTP gamma S, a non-hydrolysable analogue of guanosine triphosphate, opens promising leads to an analysis of intracellular events regulated by acetylcholine.
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006243:Harderian Gland / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D007765:Lacrimal Apparatus / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011976:Receptors, Muscarinic / Q000502:physiology*
D007473:Ion Channels; D011976:Receptors, Muscarinic; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium