Figure 6. HCN current in hES-CMs.

A, representative single cell, whole-cell patch-clamp recording of current elicited by protocol depicted in Fig. 5. Note as in Fig. 5 the slowly developing hyperpolarization-activated current. Also, on the return voltage step to +40 mV a large inward current is activated for V_test > −70 mV. Inset, expanded time scale of the return step to −40 mV showing inward current. The inward current amplitude upon return to −40 mV is a function of the preceding membrane potential value. The largest inward current amplitude was measured following a −130 mV pulse, while following the −70 mV pulse the current amplitude was approximately half-maximal. B, 2 mm Cs⁺ induced complete block of slowly developing hyperpolarization-activated current. Note the lack of effect on the rapid inward current activated by the return voltage step to −40 mV C, current–voltage plot for 2.3 s isochronal Cs⁺−sensitive current. D, time course of activation was fitted to a single exponential function; shown is the time constant of activation as a function of V_test.