Actin-based cell motility: myofibril contraction - Essay Example

Download file to see previous pages Muscle contraction is a very important physiological behavior to human. All physical movement for example lifting arms, swallowing food, heart beating involved muscles contraction. The mechanism of muscle contraction is studied by a lot of researchers.However, the most widely accepted theory was the “filament sliding model” proposed by Huxley and Niedergerke (1954), and Huxley and Hanson (1954). A skeletal muscle is made up of subunits called the fasicles. Fasicles are bundles of elongated muscle fibers which extend for the length of the muscle. The muscle fiber is segmented into distinct sectional bands. Within each muscle cell are numerous myofibrils, which also extend for the length of the muscle cell. Sarcomeres are the basic contractile subunit of myofibrils. Within the myofibrils subunit, there are thin and thick filaments. The thin filament is made up of actin while the thick filament is made up of myosin. These two filaments are the main constituent of the filament sliding model. During a muscle contraction, a crossbridge cycle was initiated. When the nervous system sends a synaptic signal to the muscle fiber through the release of acetylcholine into the synaptic clefts, it causes the sarcoplasmic reticulum to release calcium ion Ca2+. Ca2+ binds to the troponin. This activated the myosin ATPase and ATP is hydrolyzed by to ADP and Pi. ATP initially dissociates actomyosin into actin and myosin; i.e. the thick filaments will be detached from the thin filaments. It is bind to the myosin head in the thick filaments. ...
It is thought that the energy stored in the myosin molecule brings about a conformational change in the crossbridge tilting the angle from 90o to 45o. This tilting pulls the actin filament about 10 nm toward the center of the sarcomere, while the energy stored in myosin is utilized (Barane and Barane, 2002). The repeat formation and breaking of the crossbridge results the sliding of both the filament and shortening of the sarcomere (Stephen, 2000).
Thus, in this study, we aimed to observed the changes of the rabbit muscle during the contraction.

Materials and Methods:
Samples:
Glycerinated rabbit (Sylvilagus floridanus) psoas muscle.

Reagents:
100 mM KCl,
5.0 mM Pipes buffer,
4mM EGTA,
4 mM MgCl2, pH 7.0
0.1 M sodium pyrophosphate at pH 6.4.

Equipments and apparatus:
Clean microscope slides and cover glasses
Pasteur pipettes
Filter paper strips
Bucket with ice

A 2 cm segment of glycerinated rabbit (Sylvilagus floridanus) psoas muscle was soaked for 30 minutes in ice-cold standard salt solution: 100 mM KCl, 5.0 mM Pipes buffer, 4 mM EGTA, 4 mM MgCl2, pH 7.0. This washed out most of the glycerol and placed the myofibrils in the basic buffer.
The fibers and some of the salt solution were moved to a small Petri dish set inside a larger Petri dish of ice. Then, they were all placed on the stage of a dissecting microscope. Under the microscope, by using dissecting needles, the fibers were shredded longitudinally until they were less than 0.2 mm in diameter. The shredded muscle fibers were kept cold during the class and fibers were taken out as needed for observations.
A small drop containing muscle fibers was transferred by using a Pasteur pipette attached to a rubber bulb to the ...Download file to see next pagesRead More