-transparent.png){kind=logo}
In rat peritoneal mast cells, the activation of GTP-binding proteins (G proteins) by guanosine 5'-[gamma-thio]triphosphate GTP[gamma S] has been found to induce a transient rise in intracellular calcium as well as degranulation. A G protein that couples to phospholipase C (Gp) is thought to mediate the calcium response, whereas degranulation is mediated by a different G protein, termed Ge. In an attempt to activate mast-cell G proteins more selectively, the GTP analogues guanosine 5'-[alpha-thio]triphosphate (GTP[alpha S]) and guanosine 5'-[beta-thio]triphosphate (GTP[beta S]) (RP and SP diastereomers) were introduced into mast cells by means of patch pipettes. Degranulation and free intracellular calcium were monitored by cell capacitance and fura-2 measurements, respectively. It was found that RP-GTP[alpha S], like GTP[gamma S], induced both calcium release and exocytosis. In contrast, RP-GTP[beta S] induced repetitive calcium spikes that were not regularly accompanied by exocytosis. These results suggest that RP-GTP[beta S] selectively activates calcium signaling in mast cells. The RP-GTP[beta S]-induced oscillations were independent of extracellular calcium. They were absent in the presence of heparin or high concentrations of inositol 1,4,5-trisphosphate and modulated by compound 48/80, suggesting the involvement of the inositol phospholipid signaling pathway. Latency of appearance and spiking frequency were markedly modulated by varying the intracellular ATP concentration. The differential activation of intracellular calcium signaling and exocytosis by GTP[beta S] confirms the presence of independent signal-transduction pathways for the two cell responses. RP-GTP[beta S] may prove helpful in the biochemical and molecular characterization of Gp, the as-yet-unidentified G protein that couples receptors to intracellular calcium release.
F von zur Mühlen, and
F Eckstein, and
R Penner
June 1987,
Biochemical and biophysical research communications,
F von zur Mühlen, and
F Eckstein, and
R Penner
November 1992,
The Biochemical journal,
F von zur Mühlen, and
F Eckstein, and
R Penner
June 1990,
Biochemical Society transactions,
F von zur Mühlen, and
F Eckstein, and
R Penner
March 1997,
Endocrinology,
F von zur Mühlen, and
F Eckstein, and
R Penner
January 1994,
Methods in enzymology,
F von zur Mühlen, and
F Eckstein, and
R Penner
July 1999,
Archives of biochemistry and biophysics,
F von zur Mühlen, and
F Eckstein, and
R Penner
June 1992,
The Biochemical journal,
F von zur Mühlen, and
F Eckstein, and
R Penner
January 1990,
Neuroscience,
F von zur Mühlen, and
F Eckstein, and
R Penner
March 1994,
Current eye research,
F von zur Mühlen, and
F Eckstein, and
R Penner
September 1990,
The Biochemical journal,
