Thio-NADP is not an antagonist of NAADP

被引:12
作者
Deborah M. Dickey
Robert Aarhus
Timothy F. Walseth
Hon Cheung Lee
机构
[1] University of Minnesota,Department of Pharmacology
[2] University of Minnesota,Department of Physiology
关键词
NAADP; Ca; release; Thio-NADP;
D O I
10.1007/BF02738310
中图分类号
学科分类号
摘要
Nicotinic acid adenine dinucleotide phosphate (NAADP) is a metabolite of NADP, which can release Ca2+ from stores that are distinct from those activated by either cyclic ADP-ribose or inositol 1,4,5-trisphosphate (IP3). It has previously been suggested that thio-NADP is a specific antagonist of NAADP (Chini et al. [1995]J. Biol. Chem.270, 3216–3223). Its effects in sea-urchin egg homogenates were investigated. At 50 μM, thio-NADP activates partial Ca2+ release and totally inhibits subsequent challenge with a saturating concentration of NAADP. Purification by HPLC eliminates the Ca2+ releasing activity of 50 μM thio-NADP and reduces the subsequent inhibition by 73.7±1.3%. The residual inhibitory effect is no more than that exerted by 50 μM of either NADP itself or nicotinic acid adenine dinucleotide (NAAD). These results are confirmed by32P-NAADP binding studies. Unpurified thio-NADP inhibits the specific32P-NAADP binding to egg microsomes with an IC50 of 40 μM. After HPLC purification, only 20% inhibition is seen at a concentration as high as 50 μM, similar to the extent of inhibition effected by 40 μM NADP. These results indicate the inhibitory substance in thio-NADP is a contaminant. The partial Ca2+ release activity of unpurified thio-NADP suggests the contaminant is NAADP itself. This is supported by the fact that pretreatment with a subthreshold concentration of only 2 nM NAADP totally desensitizes the egg homogenates such that no Ca2+ response is seen with saturating NAADP. Estimation from the binding studies shows that a contamination of 0.012% of NAADP in the unpurified thio-NADP samples is sufficient to account for the inhibitory effects. These results indicate thio-NADP is not an antagonist of NAADP.
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页码:63 / 73
页数:10
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共 36 条
  • [11] Lee H. C.(1995) release J. Biol. Chem. 270 30,327-30,333
  • [12] Aarhus R.(undefined)Nicotinic acid-adenine dinucleotide phosphate mobilizes Ca undefined undefined undefined-undefined
  • [13] Graeff R.(undefined) from a thapsigargin-insensitive pool undefined undefined undefined-undefined
  • [14] Gurnack M. E.(undefined)Activation and inactivation of Ca undefined undefined undefined-undefined
  • [15] Walseth T. F.(undefined) release by NAADP undefined undefined undefined-undefined
  • [16] Lee H. C.(undefined)Nicotinate adenine dinucleotide phosphate (NAADP) triggers a specific calcium release system in sea urchin eggs undefined undefined undefined-undefined
  • [17] Aarhus R.(undefined)ADP-ribosyl cyclase and CD38 catalyze the synthesis of a calcium-mobilizing metabolite from NADP undefined undefined undefined-undefined
  • [18] Genazzani A. A.(undefined)undefined undefined undefined undefined-undefined
  • [19] Empson R. M.(undefined)undefined undefined undefined undefined-undefined
  • [20] Galione A.(undefined)undefined undefined undefined undefined-undefined