CHANGES IN IP3 METABOLISM DURING SKELETAL-MUSCLE DEVELOPMENT IN-VIVO AND IN-VITRO

We have investigated whether IP3 metabolism presents particular change s during critical stages of muscle development. With this aim, we have measured IP3 formation through phospholipase C activity, IP3 removal through IP3 5-phosphatase and IP3 3-kinase activities, as well as IP3 mass, during myogenesis in vivo and in vitro. In developing rat skelet al muscle, both IP3 3-kinase and 5 phosphatase activities were relativ ely constant from embryonary day 15, the earliest age studied, to post natal day 10; 5-phosphatase decreased upon further development. A tran sient, major increase in phospholipase C activity was evident at embry onary day 18 while a non-significant increase in IP3 mass was detected at this embrionary age. In rat skeletal muscle in primary culture, al l enzyme activities as well as the mass of IP3 increased significantly in myotubes compared to myoblasts. Myotubes incubated with calcitonin gene-related peptide, responded with a transient increase in IP3 mass after 2 to 10 sec; the CGRP induced increase being completely blocked by U-73122, a phospholipase C inhibitor. Furthermore, IP3 mass increa sed within 1 hr after exposure to differentiating agents of both RCMH cells, a line derived from normal human skeletal muscle, and C2C12 cel ls. These results indicate that changes in IP3 metabolism can be corre lated to critical stages of muscle development and differentiation, su ggesting a possible role for IP3 in these processes. Copyright (C) 199 7 Elsevier Science Inc.