Hormonal activation of phosphorylase in cockroach fat body trophocytes: A correlation with trans-membrane calcium flux

This study is an investigation of the temporal relationship between transme mbrane Ca2+ fluxes, and glycogen phosphorylase activation in dispersed trop hocytes from the fat body of the cockroach, Periplaneta americana. Phosphor ylase is maximally activated within 5 min after treating the trophocytes wi th either of the hypertrehalosemic hormones, Pea-HTH-I and Pea-HTH-II. Acti vation caused by Pea-HTH-II is sustained for a longer period than that prod uced by Pea-HTH-I. Chelation of extracellular Ca2+ with EGTA blocks the act ivation of phosphorylase by HTH. Similarly, chelation of intracellular Ca2 with Quin 2 greatly diminishes the phosphorylase activating effect of both HTHs. The data support the view that an increase in the intracellular Ca2 concentration is required for the activation of phosphorylase and that ext racellular Ca2+ is an essential, although not necessarily sole, source of C a2+ for this purpose. Using Ca-45(2+) to trace the movement of Ca2+ followi ng a challenge with either Pea-HTH-I or -II, it was shown that Ca-45(2+) in flux nearly doubled during the first 30 s. At this time, the trophocytes be gin to expel Ca2+ at a rate higher than that of untreated cells and this st ate persists for approximately 4 min. The Ca2+ fluxes are consistent with i ts postulated role in the activation of phosphorylase. Arch. Insect Biochem , Physiol, 42:233-244, 1999, (C) 1999 Wiley-Liss, Inc.