Comparison of Ca2+ mobilizing activities of cyclic ADP-ribose and inositol trisphosphate.

Abstract

We have previously shown that a metabolite of NAD+ generated by an enzyme present in sea urchin eggs and mammalian tissues can mobilize intracellular Ca2+ in the eggs. Structural determination established it to be a cyclized ADP-ribose, and the name cyclic ADP-ribose (cADPR) has been proposed. In this study, Ca2+ mobilizations induced by cADPR and inositol trisphosphate (IP3) in sea urchin egg homogenates were monitored with Ca2+ indicators and Ca2(+)-specific electrodes. Both methods showed that cADPR can release Ca2+ from egg homogenates. Evidence indicated that it did not act as a nonspecific Ca2(+)-ionophore or as a blocker of the microsomal Ca2(+)-transport; instead, it was likely to be operating through a specific receptor system. This was supported by its half-maximal effective concentration of 18 nM, which was 7 times lower than that of IP3. The receptor for cADPR appeared to be different from that of IP3 because heparin, an inhibitor of IP3 binding, had no effect on the cADPR action. The Ca2+ releases induced by cADPR and IP3 were not additive and had an inverse relationship, indicating overlapping stores were mobilized. Microinjection of cADPR into intact eggs induced transient intracellular Ca2+ changes and activated the cortical reaction. The in vivo effectiveness of cADPR was directly comparable with IP3 and neither required external Ca2+. In addition, both were effective in activating the eggs to undergo multiple nuclear cycles and DNA synthesis. These results suggest that cADPR could function as a second messenger in sea urchin eggs.

The NO Pathway Acts Late during the Fertilization Response in Sea Urchin Eggs

“…What we can say is that the timing of cADPR production at fertilization appears to be later than that of InsP 3 measured in a previous study (16) in L. pictus and suggests that cADPR regulates the later phase of the transient. Our data indicate cADPR levels peak at 200 nM at fertilization; cADPR levels of 40 -150 nM are reported to release Ca 2ϩ in intact sea urchin eggs on microinjection (5,10,11), so the increases we observe are physiologically relevant. One paradox is that the previously measured levels of cGMP in A. crassispina and H. pulcherrimus (18) are orders of magnitude lower than the concentration required to activate intact eggs on microinjection (46, and the present study).…”

Endogenously Bound Calmodulin Is Essential for the Function of the Inositol 1,4,5-Trisphosphate Receptor

“…The latter value was calculated by summing, in retrograde order, the amount of tracer remaining in the cells at the end of the efflux and the amounts of tracer collected during the successive time intervals. Ca 2ϩ Measurements in Sea Urchin Egg Homogenates-Agonist-induced calcium release was measured with the fluorescent dye fluo3 (3 M) (Invitrogen) using Lytechinus pictus egg homogenates as previously described (23). Briefly, homogenates were diluted successively to 2.5% final v/v over 4 h at 17°C in Glu IM (250 mM potassium gluconate, 20 mM HEPES, and 1 mM MgCl 2 (pH 7.2)) supplemented by an ATP regeneration system (1 mM ATP, 10 units/ml creatine kinase, and 10 mM phosphocreatine) together with protease inhibitors.…”

Localization of the Cyclic ADP-ribose-dependent Calcium Signaling Pathway in Hepatocyte Nucleus

“…In addition to its immuno-functions, CD38 has been shown to play an important role in insulin secretion via the cADPR-dependent calcium signaling pathway (13). Indeed, results suggest the appearance of autoantibodies to CD38 in patients may contribute to the development of noninsulin-dependent diabetes (14).The calcium stores mobilized by cADPR and NAADP have been shown to be co-purified with that sensitive to IP 3 , which is believed to be the endoplasmic reticulum (3,15,16). Increasing evidence suggests that the nuclear envelope may also be an important source of Ca 2ϩ stores.…”

“…The calcium stores mobilized by cADPR and NAADP have been shown to be co-purified with that sensitive to IP 3 , which is believed to be the endoplasmic reticulum (3,15,16). Increasing evidence suggests that the nuclear envelope may also be an important source of Ca 2ϩ stores.…”