Contractures in normal and denervated inferior oblique muscle of the rabbit

Abstract

Isometric contracture responses of normal and denervated inferior oblique muscles (IO) of the rabbit have been investigated in vitro at 35 degrees C. The threshold concentration for eliciting potassium contractures was about 20 mM K+. In normal IU low potassium concentrations up to about 50 mM K+ evoked only sustained contractures, higher concentrations were responded by contractures with an initial transient component. The transient tension development was maximal at about 100 mM K+ the sustained component at 80 mM K+. After denervation the characteristic time course of the contractures was not changed, but the tension output of the preparation was diminished and long-term denervated IO have a somewhat lowered threshold. In normal IO acetylcholine (ACh), succinylcholine (SCh) and choline (Ch) caused also sustained contractures, the threshold doses were about 5 microM for ACh and SCh and 500 microM for Ch. The ACh sensitivity of the preparations was increased by physostigmine and decreased or abolished by d-tubocurarine. Denervation increased the drug sensitivity but the shape of the contractures was hardly influenced. The properties of slow tonic muscle fibres in mammalian extraocular muscles (EOM) probably responsible for sustained contractures and their changes after denervation are discussed.

Inferior oblique muscle fixation to the orbital wall: A profound weakening procedure

“…Advantages of this procedure include reversibility and that it can be converted into another form of weakening procedure, if required. ( J AAPOS 2007;11: [17][18][19][20][21][22] I ntraocular muscle-weakening procedures can be divided into 3 categories: (1) procedures in which the muscle is reattached to the sclera, including recession, 1 anterior transposition, 2 and nasal anteriorization of the IO; 3 (2) procedures in which the muscle is weakened but is not reattached to the sclera, including disinsertion, 4 myotomy, 4 myectomy, 4,5 and extirpation; 6 and (3) denervation of the IO muscle. 7,8 Complications after IO weakening procedures include persistent overaction, marked underaction, limitation of upgaze, antielevation syndrome, subsequent overaction of the IO muscle of the opposite eye, Y-pattern exotropia in upgaze, incyclotorsion, changes in eyelid position, esotropia in upgaze, and distortion of the inferior rectus muscle.…”

“…IO myectomy corrected 14 ⌬ of vertical deviation in primary position and IO recession corrected 8 ⌬ of vertical deviation in the primary position. 19 Chang et al 11 reported 33 subjects with unilateral SO palsy who underwent anterior transposition temporal to the IR muscle insertion. The mean postoperative correction was 10 ⌬ of hypertropia in the primary position.…”

“…4,6,7,8 Animal studies showed contracture and hyper- Ela-Dalman et al trophy of the IO muscle after denervation. 18,19 The time frame between denervation and recurrent overaction of the IO muscle ranges between 2 to 5 months after nerve sectioning to 8 to 18 months after nerve excision. 7,8 In our study, 7 of 14 IO muscles had ϩ3 or more overaction preoperatively.…”

Succinylcholine activation of human horizontal eye muscles

“…The multiply innervated fibres of the global layer resemble the slow fibres of amphibian muscle, and the multiply innervated fibres of the orbital layer are similar to the so‐called intermediate muscle fibres of amphibia (Smith & Ovalle 1973; Lännergren 1979). Succinylcholine has been shown to induce contracture of eye muscles in both animals (Hess & Pilar 1963; Kern 1965; Bach‐y‐Rita & Ito 1966; Katz & Eakins 1967; Asmussen & Gaunitz 1981) and humans (Simonsz et al. 1988).…”

Specific Metabolic Properties of Rat Oculorotatory Extraocular Muscles Can Be Linked to Their Low Force Requirements

“…Tonic fibers are possibly responsible for the fact that EOMs display some properties normally observed only in muscles of lower vertebrates or in neonatal or denervated mammalian muscles (e.g., acetylcholine contractures). 23 EOMs also possess some unusual structural features: They contain very thin fibers organized in layers with abundant capillaries, 24 -26 their motor unit size is very small, 10 -12 and many fibers branch and form muscle-tomuscle junctions. 27 With electron microscopy, it has been shown that EOMs unusually contain many mitochondria and an extensive sarcotubular (SR-T) system.…”