THE METABOLIC CHARACTERISTICS OF THE LOCOMOTORY MUSCLES OF GREY SEALS(HALICHOERUS-GRYPUS), HARBOR SEALS (PHOCA-VITULINA) AND ANTARCTIC FURSEALS (ARCTOCEPHALUS-GAZELLA)
Jz. Reed et al., THE METABOLIC CHARACTERISTICS OF THE LOCOMOTORY MUSCLES OF GREY SEALS(HALICHOERUS-GRYPUS), HARBOR SEALS (PHOCA-VITULINA) AND ANTARCTIC FURSEALS (ARCTOCEPHALUS-GAZELLA), Journal of Experimental Biology, 194, 1994, pp. 33-46
It is not known precisely how marine mammals are able to maintain musc
le function during active swimming in breath-hold dives, when ventilat
ion stops and heart rate falls. Examination of muscle biochemistry and
histochemistry can provide information on the relative importance of
different metabolic pathways, the contractile potential of the muscle
fibres, the oxygen storage capacity of the muscle and the capillary di
stribution in these animals. In this study, samples of locomotory musc
le were taken from wild grey seals (Halichoerus grypus), harbour seals
(Phoca vitulina) and Antarctic fur seals (Arctocephalus gazella); Wis
tar rat muscle was analysed for comparative purposes. Activities of ci
trate synthase and beta-hydroxyacyl CoA dehydrogenase were higher in t
he harbour seal muscle than in the grey seal muscle, suggesting that h
arbour seals have a greater aerobic capacity. Both phocid muscles had
a greater reliance on fatty acid oxidation than the fur seal or rat mu
scles. The myoglobin data demonstrate that the grey seals have the hig
hest oxygen storage capacity of the three pinniped species, which corr
elates with their greater diving ability. Myoglobin levels were higher
in all three pinniped species than in the Wistar rat. The fibre type
compositions suggest that the muscles from the fur seals have higher g
lycolytic capacities than those of the phocid seals [fur seal pectoral
is, 7% slow-twitch oxidative fibres (SO), 25% fast-twitch oxidative gl
ycolytic fibres (FOG), 68% fast-twitch glycolytic fibres (FG); grey se
al 57% SO, 5% FOG, 38% FG; area per cents]. However, the pectoralis mu
scle of the fur seal, although the most glycolytic of the pinniped mus
cles studied, has the highest capillary density, which indicates a hig
h capacity for fuel distribution. These results show that, while pinni
ped muscle has an increased oxygen storage potential compared with the
muscle of a typical terrestrial mammal, there are no distinct adaptat
ions for diving in the enzyme pathways or fibre type distributions of
the pinniped muscle. However, the muscle characteristics of each speci
es can be related to its diving behaviour and foraging strategy.