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

✍ Scribed by J. E. Steele; R. Ireland

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 202 KB
• Volume: 46
• Category: Article
• ISSN: 0739-4462
• DOI: 10.1002/arch.13

✦ Synopsis

Abstract

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.