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 PeaHTH-II, Activ ation caused by Pea-HTH-II is sustained for a longer period than that produ ced by Pea-HTH-I. Chelation of extracellular Ca2+ with EGTA blocks the acti vation of phosphorylase by HTH. Similarly, chelation of intracellular Ca2with Quin 2 greatly diminishes the phosphorylase activating effect of both HTHs. The data support the view that an increase in the intracellular Ca2concentration is required for the activation of phosphorylase and that extr acellular Ca2+ is an essential, although not necessarily sole, source of Ca 2+ for this purpose. Using Ca-45(2+) to trace the movement of Ca2+ followin g a challenge with either Pea-HTH-I or -II, it was shown that (45)Ca(2+)inf lux nearly doubled during the first 30 a. At this time, the trophocytes beg in to expel Ca at a rate higher than that of untreated cells and this state persists for approximately 4 min. The Ca2+ fluxes are consistent with its postulated role in the activation of phosphorylase, (C) 1999 Wiley-Liss, In c.