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Etruscan shrew muscle: the consequences of being small

Klaus D. Jürgens^*

Zentrum Physiologie, Medizinische Hochschule, D-30623 Hannover, Germany

View larger version (15K): [in a new window]   Fig. 1. Example of isometric twitch contractions at 21°C of soleus (A) and extensor digitorum longus (B) muscle of Suncus etruscus stimulated simultaneously with a supramaximal electrical pulse of 1 ms duration. The curves are digital scans of original recordings. Time to peak force (tp) is the time between the stimulus (upward-pointing arrow) and the occurrence of maximal force, and the 50, 75 and 90% relaxation times (tr50, tr75, tr90) are the times for the decay from maximal force to 50, 25 and 10% of maximal force, respectively.

View larger version (35K): [in a new window]   Fig. 2. Myosin heavy chain composition of extensor digitorum longus (EDL) (17 pooled muscles) and soleus (SOL) (16 pooled muscles) of Suncus etruscus demonstrated by electrophoresis. Lane M, myosin heavy chains HCI and HCIId of rabbit muscles.

View larger version (16K): [in a new window]   Fig. 3. Myosin light chain composition (fLC1 and fLC2) of extensor digitorum longus (A) and soleus (B) muscle of Suncus etruscus separated by two-dimensional electrophoresis. TM, tropomyosin.

View larger version (14K): [in a new window]   Fig. 4. Ratio of lactate dehydrogenase to citrate synthase (LDH/CS) activity in gastrocnemius muscle of mammals of different body masses (Mb). The symbols represent data for Suncus etruscus () and Crocidura russula () (Peters et al., 1999) together with those for the shrew Sorex vagrans (body mass 4-5 g) ([UNK]) and several larger mammals (), taken from Emmett and Hochachka (1981). The solid line is the result of a linear regression on a double-logarithmic scale in which all data points were included: log(LDH/CS)=0.304logMb+0.623; r2=0.62).

View larger version (41K): [in a new window]   Fig. 5. Pattern of electrophoretically separated cytosolic proteins and corresponding densitograms of extensor digitorum longus (EDL) (17 pooled muscles) and soleus (SOL) (16 pooled muscles) of Suncus etruscus. CK, creatine kinase.