Maximal force potential of tetanized mammalian smooth muscle

By applying abrupt load clamps of varying magnitude at a given moment during the course of an isotonic tetanus in smooth muscle of canine trachea (TSM) and saphenous vein (CSV), it is possible to obtain a measure of the maximal load-bearing capacity of the force-producing sites in these muscles. This capacity has been termed maximal force potential (MFP). By applying such load clamps at differing times throughout the course of the tetanus and beyond, we have been able to obtain MFP curves for TSM and CSV. MFP curves for these smooth muscles differ from those for striated muscle. First, although MFP in striated cardiac muscle is only about 20% greater than tetanic force, it is up to nearly 200% greater in smooth muscle. Second and more importantly, although in striated muscle MFP curves return to zero along with the tetanic force curves, in smooth muscle MFP is maintained for long after the isometric tetanus has returned to zero.