title: Regulation of membrane potential and fluid secretion by Ca2+-activated K+ channels in mouse submandibular glands.
abstract: We have recently shown that the IK1 and maxi-K channels in parotid salivary gland acinar cells are encoded by the K(Ca)3.1 and K(Ca)1.1 genes, respectively, and in vivo stimulated parotid secretion is severely reduced in double-null mice. The current study tested whether submandibular acinar cell function also relies on these channels. We found that the K(+) currents in submandibular acinar cells have the biophysical and pharmacological footprints of IK1 and maxi-K channels and their molecular identities were confirmed by the loss of these currents in K(Ca)3.1- and K(Ca)1.1-null mice. Unexpectedly, the pilocarpine-stimulated in vivo fluid secretion from submandibular glands was essentially normal in double-null mice. This result and the possibility of side-effects of pilocarpine on the nervous system, led us to develop an ex vivo fluid secretion assay. Fluid secretion from the ex vivo assay was substantially (about 75%) reduced in animals with both K(+) channel genes ablated - strongly suggesting systemic complications with the in vivo assay. Additional experiments focusing on the membrane potential in isolated submandibular acinar cells revealed mechanistic details underlying fluid secretion in K(+) channel-deficient mice. The membrane potential of submandibular acinar cells from wild-type mice remained strongly hyperpolarized (-55 +/- 2 mV) relative to the Cl(-) equilibrium potential (-24 mV) during muscarinic stimulation. Similar hyperpolarizations were observed in K(Ca)3.1- and K(Ca)1.1-null mice (-51 +/- 3 and -48 +/- 3 mV, respectively), consistent with the normal fluid secretion produced ex vivo. In contrast, acinar cells from double K(Ca)3.1/K(Ca)1.1-null mice were only slightly hyperpolarized (-35 +/- 2 mV) also consistent with the ex vivo (but not in vivo) results. Finally, we found that the modest hyperpolarization of cells from the double-null mice was maintained by the electrogenic Na(+),K(+)-ATPase.
authors: Center for Oral Biology in the Aab Institute of Biomedical Sciences and Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.
authors: Victor G
authors: VG
authors: Romanenko
authors: Tetsuji
authors: T
authors: Nakamoto
authors: Alaka
authors: A
authors: Srivastava
authors: Ted
authors: T
authors: Begenisich
authors: James E
authors: JE
authors: Melvin
mesh_terms: D000818:Animals; D001681:Biological Assay / Q000379:methods; D002712:Chlorides / Q000378:metabolism; D003022:Clotrimazole / Q000494:pharmacology; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials; D051379:Mice; D018345:Mice, Knockout; D018721:Muscarinic Agonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051419:Paxillin / Q000494:pharmacology; D010862:Pilocarpine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D012463:Saliva / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013363:Submandibular Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002712:Chlorides; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C465449:Kcnma1 protein, mouse; C496925:Kcnn4 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D018721:Muscarinic Agonists; D051419:Paxillin; D026902:Potassium Channel Blockers; D010862:Pilocarpine; D000254:Sodium-Potassium-Exchanging ATPase; D003022:Clotrimazole; D011188:Potassium