92
H.-D. ]ANKOWSKY
In fish the red and white skeletal muscles have different structures and
functions [1, 3]. As the cytochrome oxidase activity gives a measure of the
oxidative metabolic capacity of a tissue, we compared manometrically the
activity of this enzyme in homogenates from different parts of the musculature of the silver eel. The cytochrome oxidase activity of the deeper
white muscles is approximately the same from the front and the tail of the
fish (02-uptake 160 ,ulj100 mg wet weightjhr). When one takes a peripheral muscle sample from the tail containing red fibres the enzyme activity
is much higher (02-uptake 350 ,ulj100 mg wet weightjhr). Thus the difference in the oxygen uptake of muscle from the anterior and the posterior
parts of the body is due only to the red fibres, although the amount of these
fibres is very small. Frozen sections across body musculature of adult eels
and 10 cm long young eels enable us to estimate, by measuring the areas,
that about 5 % of the muscle from the tail region consists of red fibres; in
the head region the value is still lower.
From the histological point of view the two types of muscle fibres are
markedly different. In the young eel the red musculature is 100-120 ,u
thick; the sarcoplasm-rich fibres have a diameter of about 37 ,u. They contain a lot of fat (sudan red test) and show a high succinic dehydrogenase
activity (nitro-BT test). The diameter of the white fibres is 77-110 ,u and
the succinic dehydrogenase activity is much weaker. Electron microscopic
studies show that in longitudinal sections the proportion of the total fibre
area occupied by mitochondria is less than 1 % in white fibres, but in the
red fibre approximately 15 %. The white fibres contain only a few small
mitochondria in the sarcoplasmic surface layer; between the fibrils they are
absent (Fig. 1a). In the red muscle fibre the sarcoplasmic coat is 1.5-2 ,u
thick and contains many mitochondria, especially in the neighbourhood of
capillaries. Only in the red fibres are elongated mitochondria found between the fibrils (Fig. 1 b): (1 ,u broad, up to 8.5 ,u long); attached to and
between the mitochondria lie many fat droplets.
Some preliminary investigations indicate that there are variations of
mitochondrial ultrastructure in the red muscles of eels adapted to different
temperatures; mitochondria of cold acclimated fish seem to have more
tightly packed cristae. As the oxidative capacity of certain tissues has been
correlated with the number and structure of their mitochondria, such a
change would agree with the metabolic data of eel muscle. In the Cyprinid
fish, Idus idus, an increase in the mitochondria content of muscles takes
place during the process of cold acclimation as was previously shown by
conventional staining techniques [2].
Little is known about the physiological properties of the red muscle in
fish. PROSSER [4] has measured the tonic electrical activity in the body wall
muscles of eels. There was a striking correspondence between tonic action
potentials and the tissue oxygen consumption with regard to the two ends
H.-D. ]ANKOWSKY
In fish the red and white skeletal muscles have different structures and
functions [1, 3]. As the cytochrome oxidase activity gives a measure of the
oxidative metabolic capacity of a tissue, we compared manometrically the
activity of this enzyme in homogenates from different parts of the musculature of the silver eel. The cytochrome oxidase activity of the deeper
white muscles is approximately the same from the front and the tail of the
fish (02-uptake 160 ,ulj100 mg wet weightjhr). When one takes a peripheral muscle sample from the tail containing red fibres the enzyme activity
is much higher (02-uptake 350 ,ulj100 mg wet weightjhr). Thus the difference in the oxygen uptake of muscle from the anterior and the posterior
parts of the body is due only to the red fibres, although the amount of these
fibres is very small. Frozen sections across body musculature of adult eels
and 10 cm long young eels enable us to estimate, by measuring the areas,
that about 5 % of the muscle from the tail region consists of red fibres; in
the head region the value is still lower.
From the histological point of view the two types of muscle fibres are
markedly different. In the young eel the red musculature is 100-120 ,u
thick; the sarcoplasm-rich fibres have a diameter of about 37 ,u. They contain a lot of fat (sudan red test) and show a high succinic dehydrogenase
activity (nitro-BT test). The diameter of the white fibres is 77-110 ,u and
the succinic dehydrogenase activity is much weaker. Electron microscopic
studies show that in longitudinal sections the proportion of the total fibre
area occupied by mitochondria is less than 1 % in white fibres, but in the
red fibre approximately 15 %. The white fibres contain only a few small
mitochondria in the sarcoplasmic surface layer; between the fibrils they are
absent (Fig. 1a). In the red muscle fibre the sarcoplasmic coat is 1.5-2 ,u
thick and contains many mitochondria, especially in the neighbourhood of
capillaries. Only in the red fibres are elongated mitochondria found between the fibrils (Fig. 1 b): (1 ,u broad, up to 8.5 ,u long); attached to and
between the mitochondria lie many fat droplets.
Some preliminary investigations indicate that there are variations of
mitochondrial ultrastructure in the red muscles of eels adapted to different
temperatures; mitochondria of cold acclimated fish seem to have more
tightly packed cristae. As the oxidative capacity of certain tissues has been
correlated with the number and structure of their mitochondria, such a
change would agree with the metabolic data of eel muscle. In the Cyprinid
fish, Idus idus, an increase in the mitochondria content of muscles takes
place during the process of cold acclimation as was previously shown by
conventional staining techniques [2].
Little is known about the physiological properties of the red muscle in
fish. PROSSER [4] has measured the tonic electrical activity in the body wall
muscles of eels. There was a striking correspondence between tonic action
potentials and the tissue oxygen consumption with regard to the two ends