CALCIUM-DEPENDENT SIGNAL-TRANSDUCTION BY THE HYPERTREHALOSEMIC HORMONE IN THE COCKROACH FAT-BODY

The hypertrehalosemic hormones (HrTH) are insect peptides that stimula te the fat body to synthesize trehalose. The present research investig ated the relative importance of extra- and intracellular Ca2+ for HrTH signal transduction in the fat body of the cockroach, Blaberus discoi dalis. Although trehalose synthesis could be stimulated significantly by B. discoidalis HrTH (Bld-HrTH) in the absence of Ca2+, the presence of Ca2+ was necessary to attain a maximum hormonal response. Entry of extracellular Ca2+ mediated by ionophores (A23187, ionomycin) produce d no significant hypertrehalosemic effects, whereas release of intrace llular Ca2+ by thimerosal or thapsigargin significantly stimulated tre halose synthesis. The hypertrehalosemic effect by thimerosal occurred independently of extracellular Ca2+. Dantrolene inhibits intracellular Ca2+ release, and its presence partially suppressed Bld-HrTH-dependen t hypertrehalosemia. In conclusion, the presence of either extracellul ar Ca2+ or intracellular Ca2+ enhanced the Bld-HrTH response, but agen ts that affected intracellular Ca2+ release produced the more conclusi ve effects. (C) 1995 Academic Press, Inc.