A new intact mammalian muscle preparation suitable for in vitro investigations.

IN experiments dealing with transport mechanisms for various substances in in vitro muscle preparations, the only mammalian muscle with intact cell membranes which is commonly used is the rat diaphragm. The reason is that this muscle is thin enough to be suitable for in vitro investigations and that a method has been described1 for dissecting it out with intact and undamaged cells. The diaphragm cannot, however, be accepted as a typical skeletal muscle, either anatomically or physiologically, and general conclusions drawn from work on this muscle alone are open to serious criticism2,3. Other muscles have therefore been tried3–5; but there have been great difficulties in dissecting them out with intact cells. Promising results were reported5,6 with a preparation of the extensor digitorum longus from the rat, but other authors7 have reported very inconsistent results with this preparation. We have now found that the levator ani muscle from young male rats is small enough to be suitable for in vitro investigations and that this muscle can be dissected out without damage to its cells. This muscle has been used earlier in morphological in vivo studies, mainly of the anabolic actions of various hormones8–11, and in an in vitro investigation12 as a ‘cut’ preparation.