Bovine adrenal chromaffin cells contain an inositol 1,4,5-trisphosphate-insensitive but caffeine-sensitive Ca2+ store that can be regulated by intraluminal free Ca2+

Abstract

We have characterized some properties of the caffeine-sensitive Ca2+ store in bovine chromaffin cells. Addition of 10 mM-caffeine to permeabilized cells that were allowed to sequester Ca2+ in the presence of the precipitating anion pyrophosphate induced a transient rise in free Ca2+ concentration that was blocked by 10 microM-Ruthenium Red. Caffeine was able to release Ca2+ after the InsP3-sensitive Ca2+ pool had been completely emptied, and 10 microM-InsP3 still released Ca2+ in the presence of a high dose (50 mM) of caffeine, indicating that there are selectively sensitive Ca2+ pools in these cells. The progressive hydrolysis of pyrophosphate by a cytosolic pyrophosphatase induced a spontaneous Ca2+ release after a latency. Caffeine prevented this spontaneous Ca2+ release, indicating that the pyrophosphate-sensitive Ca2+ pool was caffeine-sensitive. On varying the free Ca2+ concentration within the caffeine-sensitive pool (by using methylenediphosphonic acid, pyrophosphate or no precipitating anion), we observed that the Ca(2+)-releasing effect of caffeine was dependent on an elevated intraluminal free Ca2+ concentration. In conclusion, the caffeine-sensitive Ca2+ store in bovine chromaffin cells is largely distinct from the InsP3-sensitive Ca2+ store, and its release mechanism shares characteristics with the ryanodine receptor of muscle cells.

Intracellular Ca2+ stores of T lymphocytes: Changes induced by in vitro and in vivo activation

“…During the last few years evidence in favor of IP3-independent release mechanisms has indeed been accurnulated in various cell types [21,[31][32][33][34].…”

Ca2+ release from platelet intracellular stores by thapsigargin and 2,5-di-(t-butyl)-1,4-benzohydroquinone: relationship to Ca2+ pools and relevance in platelet activation

“…GTP-dependent release [6] and uptake [10] processes have been described in organelles that are distinct from those that affect Ins(1,4,5)PJ, and more recently a large number of studies have described Ca2l-induced Ca2+-release mechanisms (using caffeine as a pharmacological probe) from the Ins(1,4,5)P3-insensitive stores, and such mechanisms are thought to be important in the propagation of Ca2+ oscillations (e.g. [11][12][13][14]). In platelets the intracellular Ca2+ store has often been referred to as the dense tubular system [15,16] and is a membrane system that is analogous to the smooth sarcoplasmic reticulum of skeletal muscle.…”

Inositol 1,4,5-Trisphosphate- and Caffeine-Sensitive Ca2+-Storing Organelle in Bovine Adrenal Chromaffin Cells

“…Poulsen et al (29) showed that the receptors for IP3 and ryanodine are co-distributed in subfractions of microsomes by immunoblotting using specific antibodies, which supports the results of the present study. On the other hand, Cheek et al (10), and Robinson and Burgoyne (11) reported that IP3 and caffeine released Ca2+ from discrete Ca2+ stores, while Stauderman et al…”

“…On the other hand, caffeine, a powerful potentiator of Ca2+-induced Ca2+ release (CICR) from the sarcoplasmic reticulum in muscle, evoked Ca2+ mobilization and catecholamine secretion (4,6,7) in a Ca2+-free condition, and both were blocked by the CICR channel inhibitor ryanodine in an use-dependent manner in bovine adrenal chromaffin cells (5,8). Furthermore, using digitonin-permeabilized cells of the bovine adrenal medulla, IP3 was found to release Ca2+ from internal store sites (9), which was distinct from caffeine-sensitive stores (10,11). The results of these studies indicate the existence of functional Ca2+-storage sites, which are responsive to IP3 or caffeine in adrenal chromaffin cells (12).…”