Lambert R W, Maves C A, Mircheff A K
Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033.
Curr Eye Res. 1993 Jun;12(6):539-51. doi: 10.3109/02713689309001832.
Parallel arrays of Na+/H+ and Cl-/HCO3- antiporters are believed to catalyze the first step of transepithelial electrolyte secretion in lacrimal glands by coupling Na+ and Cl- influxes across acinar cell basolateral membranes. Tracer uptake methods were used to confirm the presence of Na+/H+ antiport activity in membrane vesicles isolated from rabbit lacrimal gland fragments. Outwardly-directed H+ gradients accelerated 22Na+ uptake, and amiloride inhibited 96% of the H+ gradient-dependent 22Na+ flux. Amiloride-sensitive 22Na+ influx was half-maximal at an extravesicular Na+ concentration of 14 mM. In vitro stimulation of isolated lacrimal acini with 10 microM carbachol for 30 min increased Na+/H+ antiport activity of a subsequently isolated basolateral membrane sample 2.5-fold, but it did not significantly affect Na+/H+ antiport activity measured in intracellular membrane samples. The same treatment increased basolateral membrane Na+,K(+)-ATPase activity 1.4-fold; this increase could be accounted for by decreases in the Na+,K(+)-ATPase activities of intracellular membranes. Thus, it appears that cholinergic stimulation causes recruitment of additional Na+,K(+)-ATPase pump units to the acinar cell basolateral plasma membrane. The mechanistic basis of the increase in basolateral membrane Na+/H+ antiport activity remains unclear.
据信，Na⁺/H⁺和Cl⁻/HCO₃⁻反向转运体的平行阵列通过耦合Na⁺和Cl⁻跨腺泡细胞基底外侧膜的内流，催化泪腺跨上皮电解质分泌的第一步。采用示踪剂摄取方法来证实从兔泪腺片段分离的膜囊泡中存在Na⁺/H⁺反向转运活性。外向性H⁺梯度加速了²²Na⁺摄取，而氨氯吡脒抑制了96%的H⁺梯度依赖性²²Na⁺通量。在细胞外Na⁺浓度为14 mM时，氨氯吡脒敏感的²²Na⁺内流达到半数最大。用10 μM卡巴胆碱对分离的泪腺腺泡进行体外刺激30分钟，可使随后分离的基底外侧膜样品的Na⁺/H⁺反向转运活性增加2.5倍，但对细胞内膜样品中测得的Na⁺/H⁺反向转运活性没有显著影响。相同处理使基底外侧膜Na⁺,K⁺-ATP酶活性增加1.4倍；这种增加可以通过细胞内膜中Na⁺,K⁺-ATP酶活性的降低来解释。因此，似乎胆碱能刺激导致额外的Na⁺,K⁺-ATP酶泵单位募集到腺泡细胞基底外侧质膜。基底外侧膜Na⁺/H⁺反向转运活性增加的机制基础仍不清楚。
