Fig. 3. The ionic current activated during osteoclast spreading is a potassium current. (a) Currents were recorded with a voltage ramp protocol (insert). (a) Current-voltage (I-V) relationships measured at the peak of oscillation and at the baseline. (b) Current voltage relationship of the difference current (peak—baseline) (E_rev=-75 mV, [K+]_o=5 mM). (c) I-V curves of the difference current measured in the presence of different external potassium concentrations. E_rev shifted to positive potentials when external potassium increased. (d) Plot of E_rev versus Log of the external potassium concentration. The linear regression gave a slope of 57.8 mV per decade, in agreement with a potassium current.