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 ameri cana with either of the hypertrehalosemic hormones, HTH-I or HTH-II leads t o an increase in the cytosolic concentration of Ca2+ from similar to 80 to similar to 310 nM with a rise time of approximately 110 s. The Ca2+ concent ration then declines to the resting level during the ensuing 5 min. In the absence of extracellular Ca2+ the increase in [Ca2+](i) due to HTH is limit ed to similar to 100 nM. The calmodulin inhibitors calmidazolium and W-7 al so limit to a similar degree the ability of HTH to increase [Ca2+](i). Phor bol 12-myristate 13-acetate, an activator of protein kinase C, was shown to block Ca2+ entry through the plasma membrane. Additional evidence to suppo rt the view that HTH enhances Ca influx has been ' obtained by measuring th e quenching of fura-2 fluorescence when Ca2+ is replaced with Mn2+. (C) 200 1 Elsevier Science Ltd. All rights reserved.