Membrane electrical properties of fast- and slow-twitch muscles from rats with experimental hyperthyroidism
| Autor: | Lawrence C. Sellin, Joseph J. McArdle, R.C. Garnes |
|---|---|
| Rok vydání: | 1977 |
| Předmět: |
medicine.medical_specialty
ATPase Motor nerve Action Potentials Hyperthyroidism Motor Endplate Ouabain Membrane Potentials chemistry.chemical_compound Sarcolemma Developmental Neuroscience Myofibrils Internal medicine medicine Animals Denervation Membrane potential biology Chemistry Muscles Depolarization musculoskeletal system Muscle Denervation Rats Endocrinology Neurology Thyronine biology.protein Triiodothyronine Microelectrodes medicine.drug |
| Zdroj: | Experimental neurology. 56(1) |
| ISSN: | 0014-4886 |
| Popis: | Male rats were made hyperthyroid by daily injections by Na-3,3′,5′-triiodo- l -thyronine (T3). Twenty-four hours after the 10th injection, the fast-twitch extensor digitorum longus (extensor) and the slow-twitch soleus muscles were excised from anesthetized rats. Electrical properties of single muscle fibers were evaluated with intracellular microelectrode techniques. Experimental hyperthyroidism reduced the resting membrane potential (RMP) of the extensor to −68.5 mV from the control value of −78.9 mV. In contrast, the RMP of the ipsilateral soleus remained unaltered. The frequency of miniature end-plate potentials was equivalent to control for both muscles from hyperthyroid rats, suggesting that the polarity of the motor nerve terminal was not changed. Because denervation on the 4th day of injection prevented the depolarizing action of T3, the effects of experimental hyperthyroidism and denervation on various electrical properties of the sarcolemma were compared. Ouabain caused a 10- to 12-mV decrease of RMP for the extensor and soleus muscles from control rats as well as those receiving T3. In contrast, the RMP of denervated muscle was insensitive to ouabain. Specific membrane resistance (Rm) was slightly reduced by T3, whereas denervation caused a two- to three-fold increase of Rm. The threshold and rate of rise of action potentials ( dV dt ) recorded in the control extensor were −58.2 mV and 575 V/s, respectively. The corresponding values for the soleus, −54.0 mV and 452 V/s, were significantly different. Denervation caused an overall depression of the action potential and abolished these differences as well as decreased the overshoot of the action potentials in both muscles. Experimental hyperthyroidism had no effect on the overshoot of the action potential in either muscle. However, T3 did produce alterations in dV dt and threshold of action potentials recorded in the extensor muscle. We suggest that the effects of hyperthyroidism on the RMP and action potential of muscle are not due to changes in the electrogenic pumping capacity or specific membrane resistance of the sarcolemma and that nerves can regulate the sensitivity of muscle to thyroid hormones. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|