Abstract

We have investigated whether IP 3 metabolism presents particular changes during critical stages of muscle development. With this aim, we have measured IP 3 formation through phospholipase C activity, IP 3 removal through IP 3 5-phosphatase and IP 3 3-kinase activities, as well as IP 3 mass, during myogenesis in vivo and in vitro. In developing rat skeletal muscle, both IP 3 3-kinase and 5-phosphatase activities were relatively constant from embryonary day 15, the earliest age studied, to postnatal day 10; 5-phosphatase decreased upon further development. A transient, major increase in phospholipase C activity was evident at embryonary day 18 while a non-significant increase in IP 3 mass was detected at this embrionary age. In rat skeletal muscle in primary culture, all enzyme activities as well as the mass of IP 3 increased significantly in myotubes compared to myoblasts. Myotubes incubated with calcitonin gene-related peptide, responded with a transient increase in IP 3 mass after 2 to 10 sec; the CGRP-induced increase being completely blocked by U-73122, a phospholipase C inhibitor. Furthermore, IP 3 mass increased within 1 hr after exposure to differentiating agents of both RCMH cells, a line derived from normal human skeletal muscle, and C 2C 12 cells. These results indicate that changes in IP 3 metabolism can be correlated to critical stages of muscle development and differentiation, suggesting a possible role for IP 3 in these processes.