Figure 7.
TA muscles from older rats are weaker and more sensitive to TC. Maximal tetanic force produced by TA muscles (newtons/cm2, right vertical axis) was significantly less at 30 months compared with 6 months (■ and □, respectively, **p < .05 vs 6 months). The ratio of force produced in response to nerve stimulation to force resulting from direct muscle stimulation (NS/MS, left vertical axis) in TA muscles from 6 and 30-month-old rats (Δ and ▼, respectively). For 6-month TA muscles, NS/MS decreased monotonically as TC concentration increased; neuromuscular blockade was effectively 100% with 10 μm TC. TA muscles from 30-month-old rats were more sensitive to TC: The decrease in NS/MS decreased more at lower concentrations, reaching almost 100% block by 2 μM (*p < .05 vs 6 months). TA = thyroarytenoid; TC = tubocurarine.