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Mg2+ Release Coupled to Ca2+ Uptake Operates Strictly in the Apical Domain of Liver Epithelia
Author(s) -
Cefaratti Christie
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1236-b
The very rapid release (1–2 min) of very large quantities of Mg 2+ , ~10% of the total cellular Mg 2+ content, is observed in isolated hepatocytes following stimulation by agonists leading to the increase of cellular cAMP. In addition, during Mg 2+ release, a quantitatively similar amount of Ca 2+ enters the hepatocyte which suggests a stoichiometric exchange ratio of 1Mg 2+ :1Ca 2+ . During this time, total Ca2+ accumulation into the hepatocytes is observed to be 2–3 nmol Ca2+/mg protein. The hypothesis of this study is that very large quantities of Ca 2+ are accumulated in the apical region of the liver epithelium in response to the integrated adrenergic response. Sealed vesicles derived from isolated rat apical liver plasma membranes (aLPM) were shown to operate a unidirectional, electroneutral, Ca2+/Mg2+ exchanger, which is inhibited by amiloride and imipramine. Addition of Ca 2+ to Mg 2+ ‐loaded apical LPM causes Mg 2+ release without affecting Δψ In addition, the same exchange ratio is observed in Mg 2+ ‐loaded and Ca 2+ ‐stimulated purified aLPM as in hepatocytes. An initial Ca 2+ accumulation rate of 20 nmol/mg protein x (sec) has been measured in aLPM. In conclusion, this data demonstrates 1. the presence of an electroneutral Ca 2+ /Mg 2+ exchanger functional in the apical domain of liver epithelia and 2. a novel Ca 2+ accumulation mechanism initiated by the integrated adrenergic response pathway. This could possibly serve as an additional major mechanism of cellular Ca2+ entry initiated by a b‐adrenergic response in rat liver. NIH‐HL 18708