Elevated Potassium and Possible Protective Effects of Mild Acidification on
Muscle Contractility in X. laevis Gastrocnemius Muscles
Luke Jensen, Debora Christensen (Mentor)
Dept of Biology, Drake University
INTRODUCTION
RESULTS (CONT’D)
 Muscle activity beyond the aerobic threshold causes an
accumulation of lactic acid and a loss of intracellular K+ to the
extracellular space.
2.5
Force of Contraction (N)
2
 Increasing concentration of extracellular K+ reduces contractile
function in isolated rat soleus muscle.
 Intracellular acidification reduces maximal force and velocity of
isolated skeletal muscle cells.
 Moderately elevated extracellular H+ provides a protective effect on
contractile force when paired with increased extracellular K+ in rat
soleus muscles.
Amphibian Ringer's Lactic
Acid (pH 6.85)
1.5
Amphibian Ringer's Lactic
Acid and 10 mM K+ (pH
6.85)
Amphibian Ringer's 10 mM
K+
1
Normal Amphibian Ringer's
0.5
0
0
Our objective in this study was to determine the separate andcombined
effects of lowered pH and increased K+ on:
•
Time to complete muscular fatigue in frog (Xenopus laevis)
gastocnemius muscle
Figure 1. Muscles were preincubated
for 30 minutes in their respective
solutions prior to testing
RESULTS
Force of muscle contraction
Figure 2. Muscles were mounted on
an MLT-500 force transducer. The
sciatic nerve was placed over the
stimulator and an IV drip bathed the
tissues.
•
•
4 test groups were evaluated to determine the effects of extracellular
K+ and pH on muscle fatigue (n=3/treatment).
Solutions used were:
• normal Amphibian Ringer’s solution (pH 7.45)
• Amphibian Ringer’s solution with 10 mM K+ (pH 7.45)
• Amphibian Ringer’s solution with lactic acid (pH 6.85)
• Amphibian Ringer’s solution with 10 mM K+ and lactic acid (pH
6.85)
Amphibian Ringer’s solution consists of 111 mM NaCl, 3.35 mM KCl,
2.7 mM CaCl2, 2.38 mM NaHCO3, 5.5 mM D-glucose.
Gastrocnemius muscles isolated with their sciatic nerve from pithed
frogs were incubated at room temperature for 30 minutes in their
respective solutions (Figure 1).
Gastocnemius muscles were mounted on a force transducer and
stimulated through the sciatic nerve at a supramaximal stimulus and
a frequency of 1 Hz with an ADInstruments PowerLab. Each muscle
was continuously bathed with their respective solution to prevent the
muscle and nerve from drying out (Figure 2).
Average Time to Exhaustion (hours)
METHODS
•
8
10
12
Figure 4. Average force of contraction for the first 10 minutes of
testing for each treatment group. The general trends are the
same for all groups and there were no statistically significant
deviations from the normal control (all p-values > 0.05).
• The time to exhaustion showed large differences between
treatment groups, but this was not statistically significant. The lack
of significance is likely due to insufficient sample size.
4.5
•
6
DISCUSSION
5
•
4
Time (min)
STUDY OBJECTIVES
•
2
4
• Acidosis has been implicated in inhibiting actin-myosin interactions
and increased K+ decreases the excitability of membrane of
muscle fibers during muscle fatigue.
3.5
3
• Overgaard, Hojfeldt and Nielsen (2010) found mild acidification to
have a protective effect on dynamic muscle contractions on rat
soleus muscles in the presence of elevated K+.
2.5
2
1.5
• The results of this study do not show the same protective effect to
be true for time to total muscular fatigue in frog gastrocnemius
muscles.
1
0.5
0
Normal Amphibian
Ringer's (pH 7.45)
Amphibian Ringer's
Lactic acid (pH 6.85)
Amphibian Ringer's with Amphibian Ringer's with
10 mM K+ (pH 7.45)
Lactic acid and 10 mM
K+ (pH 6.85)
Figure 3. Average hours to exhaustion for each treatment group (mean + std dev).
Lactic acid, elevated K+, and lactic acid with elevated K+ decreased the time to fatigue
compared to normal Amphibian Ringer’s by 42.3%, 67.8%, and 83.5%, respectively.
Despite this, none of the treatment groups showed a statistically significant difference
from the control group (all p-values > 0.05).
• There was no significant effect in the reduction of force of
contraction at any time point when compared to normal Amphibian
Ringer’s solution .
• Future studies should increase sample size to see if the differences
in time to exhaustion between treatment groups is an artifact of
small sample size.
ACKNOWLEDGEMENTS
I would like to thank Dr. Debora Christensen for her guidance and long hours of work on this project as well as Dr. Charisse Buising for providing the IV drip equipment.