Regulation of intracellular calcium in dispersed fat body trophocytes of the cockroach, Periplaneta americana, by hypertrehalosemic hormone

Incubation of trophocytes from dissaggregated fat body of Periplaneta americana with either of the hypertrehalosemic hormones, HTH-I or HTH-II, leads to an increase in the cytosolic concentration of Ca 2+ from ∼80 to ∼310 nM with a rise time of approximately 110 s. The Ca 2+ concentration then declines to the resting level during the ensuing 5 min. In the absence of extracellular Ca 2+ the increase in [Ca 2+] i due to HTH is limited to ∼100 nM. The calmodulin inhibitors calmidazolium and W-7 also limit to a similar degree the ability of HTH to increase [Ca 2+] i. Phorbol 12-myristate 13-acetate, an activator of protein kinase C, was shown to block Ca 2+ entry through the plasma membrane. Additional evidence to support the view that HTH enhances Ca 2+ influx has been obtained by measuring the quenching of fura-2 fluorescence when Ca 2+ is replaced with Mn 2+.