maximum isometric tetanic stresses at L 0 (the preparation length that produced the maximum isometric tetanic force) of 212☑05 and 290☑66 kN m −2 for the fibers from the outer and inner surfaces of the mantle, respectively, did not differ significantly ( P=0.29). CMP circular fibers near the inner surface of the mantle produced higher force relative to maximum isometric tetanic force, P 0, at all points along the ascending limb of the length–tension curve than CMP circular fibers near the outer surface of the mantle. We found that both the length–twitch force and length–tetanic force relationships of the obliquely striated, central mitochondria-poor (CMP) circular muscle fibers varied with radial position in the mantle wall. We tested the hypothesis that circular muscle contractile properties vary transmurally in the mantle of the Atlantic longfin squid, Doryteuthis pealeii. This transmural gradient of strain may require the circular muscle fibers near the inner and outer surfaces of the mantle to operate in different regions of the length–tension curve during a given mantle contraction cycle. During contraction of the mantle of squid, the circular muscle fibers along the inner (lumen) surface of the mantle experience circumferential strains 1.3 to 1.6 times greater than fibers along the outer surface of the mantle. Hollow cylindrical muscular organs are widespread in animals and are effective in providing support for locomotion and movement, yet are subject to significant non-uniformities in circumferential muscle strain.
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