Frequency-dependent effects of Bay K 8644 on tetanic contractions of frog skeletal muscle.

1. The effects of the calcium channel agonist, Bay K 8644 (1-100 microM), on tetanic contractions, elicited by the stimulation frequencies of 100 Hz, 50 Hz and 25 Hz for 2 s, were investigated on frog skeletal muscle fibers. 2. Although the area under the tetanic force versus time curve was greatly reduced at the stimulation frequency of 100 Hz, this effect was significantly reversed at the lower stimulation frequencies of 50 and 25 Hz, at all concentrations tested. 3. During the intracellular recordings, it was revealed that the sodium action potentials elicited with the stimulation frequency of 100 Hz for 2 s were significantly blocked. 4. Similar to mechanical recordings, the blockade of repetitively elicited action potentials was also significantly reversed at lower stimulation frequencies of 50 and 25 Hz for all concentrations of Bay K 8644 tested. 5. In conclusion, the results indicate that Bay K 8644 depresses both tetanic contractions and action potentials in a frequency-dependent manner in frog skeletal muscle fibers.