Lee Ji Eun, Nam Joo Hyun, Kim Sung Joon
Dept. of Physiology, Seoul National Univ. College of Medicine, Seoul 110-799, Korea.
Am J Physiol Gastrointest Liver Physiol. 2005 Apr;288(4):G822-31. doi: 10.1152/ajpgi.00406.2004. Epub 2004 Nov 11.
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(+)), 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(+) 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(+). 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)(-).
为了研究唾液分泌过程中离子通道与转运体之间的相互作用，我们测量了大鼠下颌下腺腺泡（RSMGA）的膜电压（V(m)）以及细胞内Ca(2+)、Na(+)（Na(+)）、Cl(-)和H(+)（pH(i)）的浓度。在短暂施加乙酰胆碱（ACh；5 μM，20 s）诱导短暂去极化后，RSMGA表现出强烈的延迟超极化（V(h,ACh)；-95 ± 1.8 mV），哇巴因可消除这种超极化。在无HCO(3)(-)的条件下，V(h,ACh)也被布美他尼阻断，布美他尼是一种Na(+)-K(+)-2Cl(-)共转运体（NKCC）的阻断剂。然而，在存在HCO(3)(-)（24 meq，用5% CO(2)鼓泡）的情况下，V(h,ACh)未被布美他尼阻断，但被Na(+)/H(+)交换体（NHE）抑制剂乙基异丙基氨氯吡咪（EIPA）抑制。同样，在无HCO(3)(-)时，ACh诱导的Na(+)增加被布美他尼完全阻断，但在存在HCO(3)(-)时仅被阻断一半。在存在HCO(3)(-)的情况下，ACh诱导pH(i)显著酸化，EIPA处理后酸化进一步增强。在无HCO(3)(-)时，施加ACh强烈加速了NKCC活性，这是通过在施加NH(4)(+)（20 mM）期间pH(i)的衰减来测量的。值得注意的是，在存在HCO(3)(-)的情况下，ACh诱导的NKCC激活在很大程度上受到抑制。总之，RSMGA中ACh诱导的阴离子分泌之后是NKCC和NHE的激活，导致Na(+)增加。细胞内Na(+)诱导的电生性Na(+)/K(+)-ATP酶激活导致V(h,ACh)。ACh对NKCC和NHE的调节受到HCO(3)(-)生理水平的强烈影响。
