Effects of halothane on functionally skinned rabbit soleus muscle fibers: A correlation between tension transient and45Ca release

The mechanism(s) involved in the halothane-induced increase in skeletal muscle contraction was studied using functionally skinned soleus muscle fibers from rabbits: For the tension study, single functionally skinned fibers were individually mounted on two pairs of forceps, with one end attached to a photodiode tension transducer. Ca²⁺-activated tension development of the contractile proteins, and Ca²⁺ uptake and release from the sarcoplasmic reticulum (SR) using caffeine-induced tension transients were studied. To measure the amount of calcium, skinned fibers at 0.1 g/ml were used and 0.075 Ci⁴⁵Ca/ml was spiked in the solution 3 (pCa 6.5 and 1 mM EGTA]) which promoted rapid loading of Ca²⁺. Halothane (1–3%) did not change the Ca²⁺]-tension relationship; 2 and 3% halothane reduced the maximum Ca²⁺-activated tension by 6–7%. Halothane (1–3%) added to the solution 3, reduced⁴⁵Ca uptake by 3, 22 and 23%; however, the subsequent caffeine-induced tension transient and⁴⁵Ca release were increased by 10–40%. During the release phase only halothane increased both caffeine-induced tension transient and⁴⁵Ca release by 20–60%. The effects of halothane on the tension transient and on the⁴⁵Ca release were comparable. There was no dose-response relationship to the effects of halothane on the above parameters. It is concluded that halothane affects the SR by increasing its membrane permeability to Ca²⁺, resulting in an increase in myoplasmic Ca²⁺] and thus in the twitch tension in skeletal muscle.