Muscarinic activation of Na+-dependent ion transporters and modulation by bicarbonate in rat submandibular gland acinus.
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)(-).
Lee
Ji Eun
JE
Dept. of Physiology, Seoul National Univ. College of Medicine, Seoul 110-799, Korea.
Nam
Joo Hyun
JH
Kim
Sung Joon
SJ
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
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