title: Muscarinic activation of Na+-dependent ion transporters and modulation by bicarbonate in rat submandibular gland acinus.
abstract: To investigate the interaction between the ion channels and transporters in the salivary fluid secretion, we measured the membrane voltage (V(m)) and intracellular concentrations of Ca(2+), Na(+) ([Na(+)](c)), Cl(-), and H(+) (pH(i)) in rat submandibular gland acini (RSMGA). After a transient depolarization induced by a short application of acetylcholine (ACh; 5 muM, 20 s), RSMGA showed strong delayed hyperpolarization (V(h,ACh); -95 +/- 1.8 mV) that was abolished by ouabain. In the HCO(3)(-)-free condition, the V(h,ACh) was also blocked by bumetanide, a blocker of Na(+)-K(+)-2Cl(-) cotransporter (NKCC). In the presence of HCO(3)(-) (24 meq, bubbled with 5% CO(2)), however, the V(h,ACh) was not blocked by bumetanide, but it was suppressed by ethylisopropylamiloride (EIPA), a Na(+)/H(+) exchanger (NHE) inhibitor. Similarly, the ACh-induced increase in [Na(+)](c) was totally blocked by bumetanide in the absence of HCO(3)(-), but only by one-half in the presence of HCO(3)(-). ACh induced a prominent acidification of pH(i) in the presence of HCO(3)(-), and the acidification was further increased by EIPA treatment. Without HCO(3)(-), an application of ACh strongly accelerated the NKCC activity that was measured from the decay of pH(i) during the application of NH(4)(+) (20 mM). Notably, the ACh-induced activation of NKCC was largely suppressed in the presence of HCO(3)(-). In summary, the ACh-induced anion secretion in RSMGA is followed by the activation of NKCC and NHE, resulting an increase in [Na(+)](c). The intracellular Na(+)-induced activation of electrogenic Na(+)/K(+)-ATPase causes V(h,ACh). The regulation of NKCC and NHE by ACh is strongly affected by the physiological level of HCO(3)(-).
authors.affiliation: Dept. of Physiology, Seoul National Univ. College of Medicine, Seoul 110-799, Korea.
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Lee
authors.forename: Joo Hyun
authors.initials: JH
authors.lastname: Nam
authors.forename: Sung Joon
authors.initials: SJ
authors.lastname: Kim
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D018678:Cholinergic Agents / Q000494:pharmacology*; D004594:Electrophysiology; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007477:Ions / Q000378:metabolism; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D049994:Sodium Potassium Chloride Symporter Inhibitors; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D013363:Submandibular Gland / Q000378:metabolism* / Q000502:physiology
chemical_list: D001639:Bicarbonates; D002352:Carrier Proteins; D018678:Cholinergic Agents; D007477:Ions; D049994:Sodium Potassium Chloride Symporter Inhibitors; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D000584:Amiloride; D012964:Sodium; D000109:Acetylcholine; C039614:ethylisopropylamiloride