Distribution of two distinct Ca2+ -ATPase-like proteins and their relationships to the agonist-sensitive calcium store in adrenal chromaff in cells

Abstract

Many cellular functions are regulated by activation of cell-surface receptors that mobilize calcium from internal stores sensitive to inositol 1,4,5-trisphosphate (Ins(1,4,5)P3). The nature of these internal calcium stores and their localization in cells is not clear and has been a subject of debate. It was originally suggested that the Ins(1,4,5)P3-sensitive store is the endoplasmic reticulum, but a new organelle, the calciosome, identified by its possession of the calcium-binding protein, calsequestrin, and a Ca2+-ATPase-like protein of relative molecular mass 100,000 (100K), has been described as a potential Ins(1,4,5)P3-sensitive calcium store. Direct evidence on whether the calciosome is the Ins(1,4,5)P3-sensitive store is lacking. Using monoclonal antibodies raised against the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum, we show that bovine adrenal chromaffin cells contain two Ca2+-ATPase-like proteins with distinct subcellular distributions. A 100K Ca2+-ATPase-like protein is diffusely distributed, whereas a 140K Ca2+-ATPase-like protein is restricted to a region in close proximity to the nucleus. In addition, Ins(1,4,5)P3-generating agonists result in a highly localized rise in cytosolic calcium concentration ([Ca2+]i) initiated in a region close to the nucleus, whereas caffeine results in a rise in [Ca2+]i throughout the cytoplasm. Our results indicate that chromaffin cells possess two calcium stores with distinct Ca2+-ATPases and that the organelle with the 100K Ca2+-ATPase is not the Ins(1,4,5)P3-sensitive store.

Caffeine-Induced Ca 2+ Transients and Exocytosis in Paramecium Cells. A Correlated Ca 2+ Imaging and Quenched-Flow/Freeze-Fracture Analysis

“…(iii) Ca 2+ release from alveolar sacs (Länge et al, 1995) shares some other properties with Ca 2+ channels in the SR (Rousseau & Meissner, 1989), like stimulation by ATP and inhibition by Mg 2+ . (iv) In cells with only diffusely distributed ER, the signal produced by caffeine is diffuse (Burgoyne et al, 1989), i.e., quite different from what we see. Concomitantly, restriction of the Ca 2+ signal in time and space, as we have documented, is in contradiction to what would be expected from diffuse activation.…”

2,5‐Di‐(tert‐butyl)‐1,4‐benzohydroquinone mobilizes inositol 1,4,5‐trisphosphate‐sensitive and ‐insensitive Ca2+ stores

“…There is convincing evidence that intracellular Ca 2+ stores are heterogeneous [6] and in bovine adrenal chromaffin cells two immunologically distinct Ca 2+-ATPases with different subcellular distribution have been reported [16]. Our results suggest that tBuBHQ inhibits Ca 2+ uptake by a fraction (about 80070) of intracellular stores that includes, but is not restricted to, the Ins(1,4,5)P3-sensitive stores.…”

The caffeine‐sensitive Ca2+ store in bovine adrenal chromaffin cells; an examination of its role in triggering secretion and Ca2+ homeostasis

“…Both of these stimuli lead to Ca 2+ activation of the subplasmalemmal exocytotic sites [2,3]. In contrast, the InsPrmobilizing agonist angiotensin II results in either no secretion or a polarized secretory response as the InsP3-sensitive store [3,5] and the intracellular Ca 2÷ signal [4] are spatially restricted. We have previously shown that, in addition to the InsP3-sensitive store, these cells also possess a caffeinesensitive Ca 2÷ store that is diffusely distributed throughout the cell [5].…”