Cyclic ADP-ribose Induces Ca2+ Release from Caffeine-insensitive Ca2+ Pools in Canine Salivary Gland Cells

Abstract

Cyclic ADP-ribose (cADPR), a novel putative messenger of the ryanodine receptor, was examined regarding its ability to mobilize Ca2+ from intracellular Ca2+ stores in isolated cells of parotid and submandibular glands of the dog. cADPR induced a rapid and transient Ca2+ release in the digitonin-permeabilized cells of salivary glands. cADPR-induced Ca2+ release was inhibited by ryanodine receptor antagonists ruthenium red, ryanodine, benzocaine, and imperatoxin inhibitor but not by the inositol 1,4,5-trisphosphate (IP3)-receptor antagonist heparin. Thapsigargin, at a concentration of 3 to 30 microM, inhibited IP3-induced Ca2+ release, while higher concentrations were required to inhibit cADPR-induced Ca2+ release. Cross-potentiation was observed between cADPR and ryanodine or SrCl2, suggesting that cADPR sensitizes the Ca2+-induced Ca2+ release mechanism. Cyclic AMP plays a stimulatory role on cADPR- and IP3-induced Ca2+ release in digitonin-permeabilized cells. Calmodulin also potentiated cADPR-induced Ca2+ release, but inhibited IP3-induced Ca2+ release. Acetylcholine and ryanodine caused the rise in intracellular free Ca2+ concentration ([Ca2+]i) in intact submandibular and parotid cells. Caffeine did not produce any increase in Ca2+ release or [Ca2+]i rise in any preparation. ADP-ribosyl cyclase activity was found in the centrifuged particulate fractions of the salivary glands. These results suggest that cADPR serves as an endogenous modulator of Ca2+ release from Ca2+ pools through a caffeine-insensitive ryanodine receptor channel, which are different from IP3-sensitive pools in canine salivary gland cells. This system is positively regulated by cyclic AMP and calmodulin.

Subpopulation of Store-operated Ca2+ Channels Regulate Ca2+-induced Ca2+ Release in Non-excitable Cells

“…Well characterized pharmacological agents that modify the activity of the RyRs in muscle cells are caffeine and ryanodine. However, in agreement with previous work in parotid acinar cells (26,28,29), we were unable to see any stimulation of Ca 2ϩ release by using up to 20 mM caffeine and inhibition or stimulation of CICR by treating the cells with up to 250 M ryanodine. Although previous work reported inhibition of cADPR-mediated Ca 2ϩ release by ryanodine in parotid cells, all the effects were observed with microsomes (29,30 -free medium and stimulated with carbachol concentrations ranging from 0.1 M to 1 mM.…”

“…Similar uncertainties exist with ryanodine. Most studies on parotid acini of inhibition by ryanodine of Ca 2ϩ release induced by cADPR used permeabilized cells or microsomes (24,29,30). One study reported inhibition of large Ca 2ϩ oscillations induced by thapsigargin by 10 -50 M ryanodine but failed to find inhibition of the response to the agonist (28).…”

Identification of a Ryanodine Receptor in Rat Heart Mitochondria

“…Surprisingly, unlike the cardiac SR-RyR, caffeine did not enhance mitochondrial ryanodine binding (n ϭ 3). Caffeine-insensitive RyR, however, have been described in canine salivary glands (30) and in Jurkat cells (31 where millimolar concentrations of Mg 2ϩ reduced the open probability of the RyR and maintained the channel in a closed state (25,26,32). Accordingly, we studied the effects of Mg 2ϩ on [ 3 H]ryanodine binding in isolated heart mitochondria and observed a 50% inhibition in presence of 0.33 mM Mg 2ϩ (n ϭ 3, Fig.…”

Sarco‐endoplasmic reticulum Ca2+ ATPase (SERCA) inhibitors identify a novel calcium pool in the central nervous system

“…Although Ca 2+ is believed to be the endogenous activator of RyR, high millimolar concentrations of caffeine activate release via this channel. Cyclic ADP‐ribose (cADPr) and nicotinic acid‐adenine dinucleotide phosphate (NAADP), have also been proposed to activate release channels located on the ER (Yamaki et al . 1998; Bak et al .…”