Download GLYCERINATED MUSCLE FIBER CONTRACTION IS DEPENDENT

Juliana Morales
April 14th, 2011
GLYCERINATED MUSCLE FIBER CONTRACTION IS DEPENDENT ON
ATP CONCENTRATION
Comment [D1]: Note the active title
INTRODUCTION
Over the course of evolution, many forms of locomotion have evolved. The
majority of these forms of locomotion use muscles to pull against a skeleton and produce
movement (Raven et al., 2008). The mechanism behind muscles contracting to move the
skeleton and produce movements is complex and requires a great deal of energy. Muscle
contraction is driven by ATP and occurs when actin and myosin filaments slide past
eachother (Rayment et al., 1993).
The brain coordinates all sensory and motor activities. When the brain sends an
impulse to a muscle to contract the impulse is received at the neuromuscular junction.
The impulse causes acetylcholine to be released, which binds to Na+ ion channels and
opens them. The opening of the Na+ ion channels causes an influx of sodium into the
muscle cell. The influx of Na+ ions into the cell causes the sarcolemma (the membrane
of the muscle cell) to depolarize. If the depolarization reaches a threshold, then an action
potential is produced. The action potential is then carried to the sarcoplasmic reticulum
by the T-tubules. Once the action potential reaches the sarcoplasmic reticulum, Ca2+ ion
channels are opened. Ca2+ then binds to troponin and causes a conformational change,
which causes tropomyosin to move and expose the myosin binding sites on the actin
filaments. Before the myosin fiber can bind to the actin filament at the binding site it
must become activated. To become activated, and ATP binds to the myosin head and
ATPase hydrolyzes the ATP molecule into ADP and an inorganic phosphate (Pi) which
Comment [D2]: The citation structure is
correct, but I don’t want you to use Raven (the
textbook). I want you to find primary articles.
both remain attached to the myosin head. The activated myosin head may then bind to
the myosin-binding site on the actin filament. When it binds to the actin the cross-bridge
is formed, the Pi is released and the power stroke begins. During the power stroke, the
myosin head rotates and pulls the actin filament closer to the center of the sarcomere
causing it to shorten and the muscle contracts. After the power stroke the ADP is
released, but the myosin remains attached to the actin filament until it hydrolyzes another
ATP. This cycles continues until the impulse stops and the Ca2+ ion channels close,
causing the myosin binding sites to be blocked by tropomyosin again. (Raven et al.,
2008)
According to Barclay (2003), a muscle shortens approximately 0.2 nm per ATP
Comment [D3]: This paragraph is a cogent
explanation of the subject matter without going
overboard.
Comment [D4]: Note how she is referring to
the paper but still CITING it properly.
used. Considering the fact that to produce movement a muscle must contract
significantly more that 0.2 nm and ATP is also used to relax the muscle, a significant
amount of ATP is used during contraction. The principle method of ATP production by
the majority of muscle fibers is oxidative phosphorylation (Korzeniewski, 1998). When
a motor impulse is received at the neuromuscular junction, it not only indirectly triggers
the myosin ATPase to hydrolyze ATP it also triggers the production of ATP in order to
support the high-energy demands of the contracting muscle (Korzeniewski, 1998). As
stated by Cooke and Bialek (1979), varying concentrations of ATP affect the force
generating cycles needed for muscle contraction (cross-bridge formation and the power
stroke). In order to test how the force generating cycles needed for muscle contractions
are affected by ATP concentrations, we exposed glycerinated muscle fibers from pigs to
5 different solutions of varying ATP concentrations. Glycerinated muscle fibers were
used so that neural stimulation and Ca2+ were not needed (Cooke and Bialek, 1979). We
Comment [D5]: Notice how this part of the
introduction begins to get more specific to the
reasons for the scientific question.
hypothesized that the highest ATP concentration in a salt solution would cause the most
muscle contraction because it would provide the most amount of energy.
Comment [D6]: Note the clear hypothesis
statement that she was able to incorporate with
the flow of the paragraph.
METHODS
Fifteen microscope slides were obtained and labeled according to what solution
Comment [D7]: If the first word of your
sentence is a number, spell the number out.
would be placed on them (3 slides per each solution). The solutions were prepared by
mixing the supplied solutions (ATP in salt solution and ATP in distilled water) with
appropriate amounts of distilled water in order to make the following solutions: 0.25%
ATP and distilled water, 0.25% ATP and salt solution, 0.10% ATP and salt solution,
0.05% ATP and salt solution. A solution with 0.00% ATP in distilled water was also
used. A piece of skeletal muscle from a pig was obtained and separated into 15 very thin
(approximately 0.2 mm in diameter) strands using a needle. Forceps were used to
transfer the muscle strands to the appropriate slides. The length of the muscle strands
was measured in centimeters with a ruler and recorded in a table. While the muscle
fibers were observed under a microscope, 5 drops of the appropriate solution were added
to the muscle fiber and the contraction of the muscle was observed. After 40 seconds the
length of the muscle strand was measured again and recorded. This was repeated for all
of the 15 muscle strands.
Comment [D8]: Note the clarity and explicit
descriptions of her methods.
RESULTS
Muscle Strand
1
Muscle strand
2
Muscle strand
3
0.25% ATP
and Distilled
water
0.25% ATP
and salt
solution
0.10% ATP
and salt
solution
0.05% ATP
and Salt
solution
0% ATP and
salt solution
Length Before
Solution
5.1
4.4
3.3
3.8
4.7
Length after
solution
2.3
4.3
3.1
3.6
4.7
% contraction
54.9%
2.2%
6.0%
5.3%
0.0%
Length Before
Solution
3.9
4.8
3.5
4.8
5.0
Length after
solution
3.2
3.6
3.4
4.6
5.0
% contraction
17.9%
25.0%
2.9%
4.2%
0.0%
Length Before
Solution
2.6
3.2
5.0
3.5
2.4
Length after
solution
2.8
2.6
4.6
3.5
2.4
% contraction
-7.3%
18.8%
8.0%
0.0%
0.0%
average % contraction
Standard deviation
21.8%
0.312859926
15.3%
0.117886951
5.6%
0.025696952
3.2%
0.027970222
0.0%
0
Table 1. Skeletal muscle fibers from pigs were used. Measurements are given in centimeters and were
taken 40 seconds after the muscle fibers were exposed to the various solutions. Prior to being exposed to
the solutions the muscle fibers were glycerinated.
Comment [D9]: The student has a clearly
labeled table with a succinct caption. The two
lines under the table is the caption.
Average Percent Contraction
Average Percent Contraction In
Various Solutions
60.0%
50.0%
40.0%
30.0%
20.0%
10.0%
0.0%
-10.0%
-20.0%
0.25% ATP 0.25% ATP 0.10% ATP 0.05% ATP
and
and salt
and salt
and Salt
Distilled
solution
solution
solution
water
0% ATP
and salt
solution
Figure 1. Skeletal muscle fibers from pigs were used. Measurements were taken 40 seconds after the
muscle fibers were exposed to the various solutions. Prior to being exposed to the solutions the muscle
fibers were glycerinated.
Comment [D10]: This is what your graphs
should look like aesthetically. Clean, white
background, well labeled without unnecessary
legends… and labeled FIGURE 1,2 etc…
On average, the solution that caused the most percent muscle contraction in 40
seconds was the 0.25% ATP solution in distilled water, but the standard deviation was
very high (Figure 1). The 0.25% ATP in salt solution produced the second highest
percent of muscle contraction on average, followed by the 0.10% ATP in salt solution,
Comment [D11]: In the Results paragraph the
student basically does fact stating but refers to
the tables and figures when doing so.
the 0.05% ATP in salt solution, and 0% ATP in salt solution (Table 1). The 0% ATP in
salt solution did not cause the muscle to contract at all (Table 1).
DISCUSSION
Our results both contradicted and supported our hypothesis that the highest ATP
concentration in a salt solution would cause the most muscle contraction because it would
provide the most amount of energy. When muscles contract, the force generating cycles
require a large amount of energy in the form of ATP (Cooke and Bialek, 1979). In order
Comment [D12]: In the case of ambiguous
results the student addresses the hypothesis
accordingly.
to accommodate for the significant increase in ATP usage between a resting muscle and a
contracting muscle when a motor impulse is received at a neuromuscular junction the
production of ATP by oxidative phosphorylation is triggered (Korzeniewski, 1998).
Thus, the amount of force generating cycles and the amount of contraction is limited by
the amount of ATP present in a muscle cell when an action potential is generated.
Research of this kind is important because it could give us a better understanding of how
muscle uses ATP and it could possible give insight to muscle fatigue and diseases
affecting the contraction of muscle.
Comment [D13]: Good re-explanation of the
theory
Our results support the majority of the research previously conducted on this
topic. In a study done by Cooke and Bialek in (1979) it was shown that the velocity of
glycerinated muscle contraction increased with ATP concentration. A study conducted
Comment [D14]: Here, the student
incorporates her work into other research
by He et al. (2000) on human muscle fibers also supports our results. They found that
during the shortening phase of muscle contraction the rate of ATP consumption increased
proportionally to the shortening velocity. These findings are consistent with our results
because when ATP concentration was increased, there was also an increase in the average
percent of muscle contraction. This is comprehensible because the only factor limiting
muscle contraction in both our system and the system used in Cooke and Bialek’s
experiment was ATP due to the muscle being glycerinated and not needing an electrical
impulse or Ca+ ions to contract. Therefore, the more ATP present, the more the muscle
was able to contract.
As previously stated, our results both contradicted and supported our hypothesis.
We predicted that the highest concentration of ATP would cause the muscle to contract
the most. This part of our hypothesis was consistent with out results because the solution
that caused the highest average percent of contraction was the 0.25% ATP in distilled
water. We also predicted that the solution that caused the muscle to contract the most on
average would be a salt solution. This prediction was not supported by our results.
However, the solution that we predicted to cause the most muscle contraction, 0.25%
ATP in salt solution, caused the second highest average percent of contraction and had a
significantly smaller standard deviation than the 0.25% ATP in distilled water solution.
The percent muscle contraction for each trial in the 0.25% ATP in salt solution and
0.25% ATP in distilled water were not precise and they were erratic, while the percent
muscle contraction for the 0.10% ATP in salt solution, the 0.05% ATP in salt solution
and the 0.0% ATP in distilled water solutions were relatively precise and consistent. The
third trial of 0.25% ATP in distilled water actually got longer by 7.3%. The
impreciseness of the results of the 0.25% ATP solutions could be attributed to sources of
error. One possible source of error is that students prepared the ATP solutions and there
could have been contamination or miscalculations while they were preparing the
solutions and while the solutions were being applied to the muscle fibers. Our results do
allow us to conclude that muscle contraction increases with increasing ATP
concentrations, but due to the impreciseness, great variability between trials and
relatively small difference between the average percent contraction of both 0.25%
solutions, we cannot conclude that the salt solution vs. the distilled water made a
significant difference in the results.
Comment [D15]: Mentioning of error is
important
REFERENCES
Barclay, C. 2003. Models in which many cross-bridges attach simultaneously can explain
the filament movement per ATP split during muscle contraction. International
Journal of Biological Macromolecules. 32:139–147.
Cooke, R, and Bialek, W. 1979. Contraction of Glycerinated Muscle Fibers as a Function
of the ATP Concentration. Biophys. J. 28:241-258.
Korzeniewski, B. 1998. Regulation of ATP supply during muscle contraction: theoretical
studies. Biochem. J. 330:1189–1195.
Rayment, I, Holden, H, Whittaker, M, Yohn, C, Lorenz, M, Holmes, K, Milligan, R.
1993. Structure of the Actin-Myosin Complex and Its Implications for Muscle
Contraction. Science. 261:58-65.
Raven, P., H., Johnson, G., B., Losos, J., B., Mason, K., A., Singer, S., R. 2008. Biology.,
9th Edition. Pearson Education, Inc., CA.
Comment [D16]: You can use Microsoft’s
reference style, but ensure that you are
consistent.