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 transmembrane Ca 2+ fluxes, and glycogen phosphorylase activation in dispersed trophocytes from the fat body of the cockroach, Periplaneta americana . Phosphorylase is maximally activated within 5 min after treating the trophocytes with either of the hypertrehalosemic hormones, Pea‐HTH‐I and Pea‐HTH‐II. Activation caused by Pea‐HTH‐II is sustained for a longer period than that produced by Pea‐HTH‐I. Chelation of extracellular Ca 2+ with EGTA blocks the activation of phosphorylase by HTH. Similarly, chelation of intracellular Ca 2+ with Quin 2 greatly diminishes the phosphorylase activating effect of both HTHs. The data support the view that an increase in the intracellular Ca 2+ concentration is required for the activation of phosphorylase and that extracellular Ca 2+ is an essential, although not necessarily sole, source of Ca 2+ for this purpose. Using 45 Ca 2+ to trace the movement of Ca 2+ following a challenge with either Pea‐HTH‐I or ‐II, it was shown that 45 Ca 2+ influx nearly doubled during the first 30 s. At this time, the trophocytes begin to expel Ca 2+ at a rate higher than that of untreated cells and this state persists for approximately 4 min. The Ca 2+ fluxes are consistent with its postulated role in the activation of phosphorylase. Arch. Insect Biochem. Physiol. 42:233–244, 1999. © 1999 Wiley‐Liss, Inc.