Regulation of membrane potential and fluid secretion by Ca2+-activated K+ channels in mouse submandibular glands.
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.
Romanenko
Victor G
VG
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.
Nakamoto
Tetsuji
T
Srivastava
Alaka
A
Begenisich
Ted
T
Melvin
James E
JE
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*
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