Figure 7. The twitch amplitude and membrane current of two different cells under whole-cell voltage clamp. One cell was exposed to 0.25 mM halothane (0.5 vol%) and the other to 0.31 mM isoflurane (0.8 vol%). The enlarged beats shown in the lower panels were taken from times just before anesthetic introduction, just after introduction, and near the end of the record in the ongoing presence of the anesthetic, respectively. In each case, the early changes in twitch amplitude appear to be dissociated from changes in the calcium current. In both experiments, sodium currents were blocked with 20 micro Meter tetrodotoxin, and potassium currents were blocked with 4.9 mM Caesium sup + in the extracellular solution and with 120 mM Caesium sup + in the electrode-filling solution. The holding potential was -60 mV with steps to 0 mV lasting 105 ms.