If the skinned muscle fibre is immersed in the salt solution similar to intracellular muscle cytoplasm and also contains Ca2+, the cell membrane of the fibres will become impermeable for small molecules like ATP because the permeability of the cells depend on the concentration of free ionized calcium Ca2+ in cytoplasm.
This can be explained with the help of an example. Put the whole muscle fibres in the Ca2+ indicatorfura-2 conjugated to high molecular weight dextran. The fluorescence when measured from cytoplasm was found 17 degrees C (Isaevaand & Shirokova, 2003). The fluorescence excitation spectrum of fura dextran was turned slightly red in resting fibres compared with the spectrum of the Ca (2+)-free indicator in buffer solutions.
If we compare the spectra in the cytoplasm and in the vitro solutions, we find an apparently "negative" cytoplasm (Ca2+), which probably reflects an alteration of the indicator properties in the cytoplasm. To change the indicator's fluorescence signal in terms of cytoplasm [Ca2+], we applied beta-escin to permeabilize the cell membrane of the fibres immersed in fura dextran.
After treating this fibre with 5micro M beta-escin for 30 to 35 minutes, the cell membrane becomes permeable to small molecules like Ca2+, ATP, etc, whereas the 10-kD fura dextran only slowly leaked out of the fibre. Thus, it is possible to estimate calibration parameters in the indicator fluorescence in the fibres by changing the bathing solution [Ca2+] to various levels (Watanabe & Konishi, 1995).
The other substances essential for being the muscle fibre impermeable are fura dextran, MW approximately 10,000 and 0.52 microM.
The muscle fibre will remain permeable in absence of these substances for all kinds of substances.
Mechanism of graded skeletal muscle contraction in quadriceps:
There are many factors which are responsible for the contraction in quadriceps one of them is the force per fibre cross sectional area. Number of mitochondria which is present in the fibre plays important role in the supply of energy through the help of oxidative metabolism. With ageing cross sectional area of muscle tend to decrease due to decrease in the area of type 2 fibres and as a result of this a reflex which is termed as knee jerk reflex takes place. A specific kind of ligament namely strike patellar stretches the muscle of quadriceps and activate the sensory neuron which in turn synapses with the α-motor neuron to quadriceps and results in the contraction of quadriceps (Frueh, Hayes, Lynch & Williams, 1994, March 1).
Mechanism of graded skeletal muscle contraction in extra ocular muscle of the eye:
Movement of eyes is controlled by extra ocular muscles which are six in number and their actions depend upon the position of eye. Contraction in these muscles can be achieved by the experiment of temperature sensitivity (10-35 degrees C). Superior rectus and levator palpebrae superioris are the two muscles which show different response toward the temperature sensitivity. Superior rectus show fast contraction at 20 degree C then levtor but on the other hand produces lower maximum force level. Superior rectus show recreation phase which is biphasic in nature as a result of twitch response.
There are many antioxidants which alter the rate of skeletal muscle fatigue in different manner. Take a single fibre which is isolated from digitorum brevis of mouse. The antioxidant Tiron slowed down the rate of fatigue at 37ºC when compared to room temperature (22ºC). To measure intracellular calcium, single fibres were mixed with indo-1. A large decrease in myofibrillar Ca2+ sensitivity is responsible for the increased rate of fatigue at body temperature (37°C). The presence of Tiron is responsible for the decline of Ca2+ sensitivity and simultaneously decline in tetanic [Ca2+]i was noticed (Moopanar & Allen, 2005).
Mechanism: Single fibres were dissected from digitorium brevis muscle