1. Archive
2. Vol.56, No.6

Organelles Containing Inositol Trisphosphate Receptor Type 2 in Adrenal Medullary Cells

Abstract: To identify which organelles contained inositol trisphosphate (InsP₃) receptor type 2 (InsP₃R2) in adrenal medullary (AM) cells, immunocytochemical and biochemical studies were performed on AM cells of several species. InsP₃R2-like immunoreactive materials produced by two different anti-InsP₃R2 antibodies (Abs) (Chemicon and Sigma) were distributed in rat AM cells in agreement with BODIPY-FL-InsP₃ binding sites. For two other Abs (KM1083 and Santa Cruz), some of the anti-InsP₃R2 immunoreactive materials were stained with an anti-dopamine-β-hydroxylase Ab, but not by BODIPY-FL-InsP₃. BODIPY-FL-thapsigargin binding sites were consistent with a distribution of the endoplasmic reticulum (ER) identified by an anti-calnexin Ab, and a prior application of thapsigargin significantly eliminated BODIPY-FL-thapsigargin bindings, suggesting that BODIPY-FL-thapsigargin bindings were mediated by thapsigargin, but not the fluorescence molecule. The anti-InsP₃R2 Ab that produced stainings consistent with BODIPY-FL-InsP₃ bindings recognized a protein with about 250 kDa. A fractional analysis of bovine adrenal medullae revealed that the 250 kDa InsP₃R2 was detected in a crude membrane fraction, but not in a secretory granule fraction. The results suggest that the InsP₃R2 was present in the ER, but not in secretory granules in AM cells.

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