Figure 7.
Ito,f is selectively blocked by HpTx-3. Outward currents were recorded in mouse ventricular myocytes isolated from the apex and septum as described in Fig. 1 during 4.5-s depolarizing voltage steps to potentials between −20 and +60 mV from a holding potential of −70 mV; A–C in each panel were obtained from the same cell. In each cell, control currents (A) were recorded before exposure to 100 or 300 nM HpTx-3; outward K+ currents were again recorded after the effect of HpTx-3 reached a steady state (B). (B) The currents in the presence of HpTx-3 are plotted as solid lines, and the control records (A) are replotted as points to facilitate comparison. Off-line digital subtraction of the currents in the presence of HpTx-3 (B) from the controls (A) revealed that only the rapidly inactivating K+ current, Ito,f, in apex and septum cells is affected by HpTx-3 (C). Similar results were obtained in experiments on four cells. Scale bars, 2 nA and 500 ms.