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Contraction-induced glucose transport into skeletal muscle : the involvement of protein kinase C
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Abstract
The role of PKc as a possible intracellular mediator of
exercise-induced increase in skeletal muscle glucose transport was
investigated. Two skeletal systems were used, the in vivo rat
gastrocnemius-plantaris-soleus muscle preparation, and the in vitro
isolated soleus muscle preparation.
PKc was partially purified from gastrocnemius-plantarissoleus
skeletal muscle preparations by DE52 anion exchange
chromatography. The skeletal muscle content of PKc was found to be
higher than previously reported. Levels of PKc activity were found to be
comparable to those of published PKa values, which suggest an equally
important function for PKc in cellular events. The complete extraction of
PKc from skeletal muscle membranes required a high concentration of
Triton X100. This suggested that the hydrophobic domain of the enzyme
was tightly bound to the membrane bilayer. Analysis of the intracellular
distribution showed that a large proportion of the enzyme activity (60%)
was associated with the membrane component of resting muscle.
Electrical-induced contraction of the gastrocnemius‘ -
plantaris-soleus muscle group resulted in a time-dependent translocation
of PKc and a 2-fold increase in the concentration of both diacylglycerol
and phosphatidic acid. The maximal values for the latter were reached at
2 min and preceded the maximum translocation of PKc (10 min). No
PKm formation was detected by the production of a Ca 2+ -,
phospholipid-independent histone kinase activity. No reversal of
translocated PKc or decrease in the concentrations of diacyglycerol and
phosphatidic acid occurred after 30 min of rest following a 5 min period
of stimulation in vivo. The translocation of PKc was not influenced by
variations in applied load at maximal fiber recruitment, but was
dependent on the frequency of non-tetanic stimuli reaching a maximum
at 4 Hz. Thus, it is concluded that electrical-induced muscle contraction
increased the production of diacylglycerol and the translocation of PKc.
This is indictative of enzyme activation.
The relationship between PKc and glucose transport was
explored, in vivo, by varying the number of tetanic stimuli. Only one train
of stimuli (200 ms, 100 Hz) was required for maximum translocation of
PKc and for diacylglycerol and phosphatidic acid production. However,
more than 35 trains of stimuli were required to activate glucose transport.
The electrical stimulation of isolated soleus muscle in vitro increased the
rate of glucose transport, but this required 20 min to reach maximum.
Therefore, the time course for the activation of glucose transport is
slower than PKc translocation. Thus, it is concluded that a "causal"
relationship between electrical stimulation and the increase in glucose
transport involving PKc activation may exist.
In an attempt to further clarify a role for PKc in the
mechanism of glucose transport activation isolated soleus muscle was
depleted ("downregulated") of PKc activity by prolonged TPA treatment.
The response to both insulin and contraction in terms of glucose
transport was assessed. Muscles treated with TPA showed an increased
basal rate of 3-0-methylglucose uptake, responded partially to insulin,
but did not respond to contraction. The TPA treated and non-treated
muscles were indistinguishable in terms of pre-contraction content of
adenine nucleotide, creatine phosphate, lactate and glycogen, as well as
contractile performance and contraction-induced glycogenolysis. Thus, it
is concluded that treatment of isolated soleus muscle with TPA gives rise
to a marked loss of contraction-induced glucose transport.
Overall, the work embodied by this thesis supports a case
for the involvement of PKc in contraction-mediated uptake of glucose by
skeletal muscle.
| Item Type: | Thesis - PhD |
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| Authors/Creators: | Cleland, Perry J F |
| Keywords: | Protein kinases, Muscles |
| Copyright Holders: | The Author |
| Copyright Information: | Copyright 1990 the Author - The University is continuing to endeavour to trace the copyright |
| Additional Information: | Includes bibliographical references (leaves 110-127). Thesis (Ph.D.)--University of Tasmania, 1991 |
| Item Statistics: | View statistics for this item |
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