DIHYDROPYRIDINE EFFECTS ON SKELETAL-MUSCLE FATIGUE

1-degree The purpose of this investigation was to determine if alterations in extracellular calcium (Ca2+) influx by the dihydropyridine derivatives Bay K 8644 and nifedipine affected skeletal muscle fatigue. 2-degrees Tetanic contractions (80 Hz, 100 msec) of frog sartorius muscles were evoked every sec for 3 min. Muscles were fatigued in normal Ringer's solution (NR), in NR containing 1-mu-M nifedipine of 10-mu-M Bay K 8644 or in low CA2+ Ringer's. 3-degrees In each case, the experimental conditions increased the rate and magnitude of fatigue. Rate constants of fatigue obtained during Bay K 8644, nifedipine and low Ca2+ conditions (- .0122 +/- .0016, - .0397 +/- 0022 and 0.0169 +/- .0064 sec-1, respectively) were significantly greater than NR (- .0104 +/- .0006 sec-1, p < .05). In addition, tetanic forces developed at the end of the stimulation period under the experimental conditions (3.90 +/- 0.81, 1.21 +/- 1.40 and 2.04 +/- 1.10% of initial) were significantly less than NR (7.18 +/- 1.27%, p < .05). 4-degrees Caffeine contracture forces (10 mM) evoked immediately after stimulation were not significantly different between conditions. 5-degrees These results suggest that alterations in sarcolemmal Ca2+ exchange has some influence on the fatigue process.