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: 1999
• Tongue: English
• Weight: 264 KB
• Volume: 42
• Category: Article
• ISSN: 0739-4462
• DOI: 10.1002/(sici)1520-6327(199912)42:4<233::aid-arch2>3.0.co;2-3

✦ Synopsis

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.