Lockwich T, Ambudkar I S, Shamoo A E
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, MD 20892.
Membr Biochem. 1993 Jul-Sep;10(3):171-9. doi: 10.3109/09687689309150264.
This study examines the Ca2+ permeability of basolateral plasma membrane vesicles (BLMVs) isolated from the rat parotid gland by monitoring the rate of 45Ca2+ efflux from actively-loaded (via the Ca(2+)-ATPase) inside-out BLMVs. Ca2+ efflux from BLMVs into a K(+)-gluconate medium which hyperpolarizes the cytoplasmic side (i.e. outside) of the inside-out BLMVs resulted in a faster rate of Ca2+ efflux compared with a control medium containing N-methyl-D-glucamine (NMDG)-gluconate. Conversely, Ca2+ efflux into a medium which depolarizes the cytoplasmic side of the BLMVs (NMDG-chloride) resulted in slower rates of efflux compared with those observed with the control medium. This increased rate of 45Ca2+ efflux from the hyperpolarized BLMV was inhibited by 1 mM Ni2+, yielding a rate of efflux similar to the rate observed in depolarized BLMVs. The rate of Ca2+ efflux from BLMVs was affected by [Ca2+]o ([Ca2+] on the extravesicular, cytoplasmic side of the vesicle). When [Ca2+]o was kept > 200 nM during efflux, the rate of Ca2+ efflux from both hyper- and depolarized BLMVs was slow and relatively unresponsive to changes in [Ca2+]o, despite sizeable changes in the Ca2+ gradient across the BLMV. However, when [Ca2+]o was lowered < 200 nM, there was an abrupt increase in the rate of Ca2+ efflux from both hyper- and depolarized BLMVs. Additionally, when [Ca2+] was < 200 nM, the rate of Ca2+ efflux appeared to be more sensitive to driving force changes. These data suggest that Ca2+ permeability across the rat parotid gland basolateral plasma membrane is modulated by membrane potential and [Ca2+] on the cytoplasmic side.
本研究通过监测主动加载（通过Ca(2+)-ATP酶）的内翻式腮腺基底外侧质膜囊泡（BLMVs）中45Ca2+的外流速率，研究了从大鼠腮腺分离出的基底外侧质膜囊泡（BLMVs）的Ca2+通透性。与含有N-甲基-D-葡糖胺（NMDG）-葡糖酸盐的对照培养基相比，从BLMVs向使内翻式BLMVs的细胞质侧（即外侧）超极化的K(+)-葡糖酸盐培养基中的Ca2+外流导致更快的Ca2+外流速率。相反，与对照培养基相比，向使BLMVs的细胞质侧去极化的培养基（NMDG-氯化物）中的Ca2+外流导致较慢的外流速率。从超极化的BLMV中增加的45Ca2+外流速率被1 mM Ni2+抑制，产生的外流速率类似于在去极化的BLMV中观察到的速率。BLMVs的Ca2+外流速率受[Ca2+]o（囊泡外侧、细胞质侧的[Ca2+]）影响。当外流期间[Ca2+]o保持>200 nM时，超极化和去极化的BLMVs的Ca2+外流速率都很慢，并且对[Ca2+]o的变化相对不敏感，尽管跨BLMV的Ca2+梯度有相当大的变化。然而，当[Ca2+]o降低到<200 nM时，超极化和去极化的BLMVs的Ca2+外流速率都突然增加。此外，当[Ca2+]<200 nM时，Ca2+外流速率似乎对驱动力变化更敏感。这些数据表明，大鼠腮腺基底外侧质膜的Ca2+通透性受膜电位和细胞质侧[Ca2+]的调节。
