Calcium-dependent signal transduction by the hypertrehalosemic hormone in the cockroach fat body.

The hypertrehalosemic hormones (HrTH) are insect peptides that stimulate the fat body to synthesize trehalose. The present research investigated the relative importance of extra- and intracellular Ca2+ for HrTH signal transduction in the fat body of the cockroach, Blaberus discoidalis. 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) produced no significant hypertrehalosemic effects, whereas release of intracellular Ca2+ by thimerosal or thapsigargin significantly stimulated trehalose synthesis. The hypertrehalosemic effect by thimerosal occurred independently of extracellular Ca2+. Dantrolene inhibits intracellular Ca2+ release, and its presence partially suppressed Bld-HrTH-dependent hypertrehalosemia. In conclusion, the presence of either extracellular Ca2+ or intracellular Ca2+ enhanced the Bld-HrTH response, but agents that affected intracellular Ca2+ release produced the more conclusive effects.