Adenophostin A induces spatially restricted calcium signaling in Xenopus laevis oocytes

The activation of intracellular calcium release and calcium entry across th e plasmalemma in response to intracellular application of inositol 2,4,5-tr isphosphate and adenophostin A, two metabolically stable agonists for inosi tol 1,4,5-trisphosphate receptors, was investigated using Xenopus laevis oo cytes and confocal imaging. Intracellular injection of inositol 2,4,5-trisp hosphate induced a rapidly spreading calcium signal associated with regener ative calcium waves; the calcium signal filled the peripheral regions of th e cell in 1-5 min. Injection of high concentrations of adenophostin A (250 nM) similarly induced rapidly spreading calcium signals. Injection of low c oncentrations of adenophostin A resulted in calcium signals that spread slo wly (>1 h). With extremely low concentrations of adenophostin A (similar to 10 pM), stable regions of Ca2+ release were observed that did not expand t o peripheral regions. When the adenophostin A-induced calcium signal was re stricted to central regions, compartmentalized calcium oscillations were so metimes observed. Restoration of extracellular calcium caused a rise in cyt oplasmic calcium restricted to the region of adenophostin A-induced calcium mobilization, The limited diffusion of adenophostin A provides an opportun ity to examine calcium signaling processes under spatially restricted condi tions and provides insights into mechanisms of intracellular calcium oscill ations and capacitative calcium entry.