# CONTROL OF ENZYME LEVELS IN SKELETAL MUSCLE CELLS

> **NIH NIH R01** · WASHINGTON UNIVERSITY · 1987 · $93,556

## Abstract

The fibers that compose mammalian skeletal muscles may differ greatly in
both twitch speed and levels of enzymes of energy metabolism.  Evidence
suggests that this heterogeneity is caused by differences in the patterns
of contractile activity among the fibers.  Increased muscle activity in
vivo is associated with increases in enzymes of oxidative energy metabolism
and decreases in glycolytic enzymes.  The mechanisms involved have not been
established, due in part to experimental limitations imposed by working
with whole animals.  I propose to use muscle cell culture to define ways in
which muscle activity and differentiation control enzyme levels.  In the
absence of nerve, cultured muscle cells develop high levels of glycolytic
enzymes and low levels of oxidative enzymes.  Primary cultures of rat
myotubes will be electrically stimulated to determine if increased activity
(in the absence of neural influences) is sufficient to promote conversion
to a more oxidative enzymatic complement.  Pharmacological evidence
suggests that the effects of muscle activity on enzyme levels are mediated
by calcium.  To investigate further, we will determine the effects of
electrical stimulation and the divalent cation ionophore, A23187, on the
rates of synthesis and degradation of selected enzymes.  These experiments
should provide information concerning the mechanisms by which calcium and
muscle activity change enzyme levels.  Under appropriate conditions,
cultured myotubes contract spontaneously, so that the effects of activity
may be investigated by comparing active cells to cells paralyzed with
tetrodotoxin.  Using this strategy, we have shown that muscle activity
leads to an increase in phosphorylase degradation and a fall in the level
of the enzyme.  The mechanism of the activity-dependent control of
degradation will be investigated in both cultured myotubes and skeletal
muscle in organ culture.  A key enzyme in regulating phosphorylase activity
is phosphorylase kinase.  The enzyme is composed of 4 nonidentical subunits
(Alpha, Beta, Gamma, Delta)4.  Red and white skeletal muscles contain
isozymes that differ in the molecular weight of the Alpha subunits.
Preliminary experiments indicate that both isozymes exist in cultured
myotubes, and that interconversion of isozymes can be accomplished by
modifying the contractile activity of these cells.  I now propose to
investigate the influences of differentiation and muscle activity on the
synthesis, degradation, and assembly of the kinase subunits.

## Key facts

- **NIH application ID:** 3156962
- **Project number:** 5R01AR034815-03
- **Recipient organization:** WASHINGTON UNIVERSITY
- **SAM.gov UEI:** L6NFUM28LQM5
- **Principal Investigator:** JOHN C. LAWRENCE
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1987
- **Award amount:** $93,556
- **Award type:** 5
- **Project period:** 1985-09-23 → 1991-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/3156962

## Citation

> US National Institutes of Health, RePORTER application 3156962, CONTROL OF ENZYME LEVELS IN SKELETAL MUSCLE CELLS (5R01AR034815-03). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/3156962. Licensed CC0.

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