Volume 272, Number 27, Issue of July 4, 1997 pp. 16984-16989
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

Cyclic ADP-ribose-gated Ca²⁺ Release in Sea Urchin Eggs Requires an Elevated [Ca²⁺]

(Received for publication, March 11, 1997, and in revised form, April 30, 1997)

From the Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322

Cyclic ADP-ribose (cADPr) has been shown to release intracellular Ca²⁺ from sea urchin eggs and a variety of vertebrate cell types, although its mechanism of action remains elusive. We employed the caged version of cADPr to study the [Ca²⁺] transient kinetics in intact sea urchin eggs for insights into how cADPr gates Ca²⁺ release. Ca²⁺ release triggered by photolytic production of cADPr was initially slow, with an effective delay of several hundred milliseconds before the onset of a rapid Ca²⁺ release phase. In contrast, Ca²⁺ release induced by photolysis of caged inositol 1,4,5-trisphosphate was immediate in onset and roughly an order of magnitude faster. The delay before cADPr-induced Ca²⁺ release was eliminated when the [Ca²⁺] was step-elevated coincident with the photoliberation of cADPr and greatly prolonged in the presence of exogenous Ca²⁺ buffers. Thus, the slow onset of Ca²⁺ release does not reflect an intrinsically slow rate by which cADPr gates release channels. Rather, a [Ca²⁺] rise from resting levels is needed to achieve more than minimal cADPr activity. Full release of Ca²⁺ by cADPr in intact sea urchin eggs requires a positive Ca²⁺ feedback.

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