Fig. 4: Characterization of BK_Ca-channel activity recorded from undifferentiated amniotic fluid-derived stem cells (AFSCs).

Cells were bathed in a high K⁺ solution containing 0.1 μM Ca²⁺. a Original BK_Ca currents for different levels of membrane potential (indicated on the upper part of each trace). The upward deflection indicates an opening event of the BK_Ca channel. b Based on the I–V relationship of BK_Ca channels, the single-channel conductance in these undifferentiated AFSCs was 185 ± 4 pS (n = 11). Note that the dashed line indicates the reverse potential (i.e., 0 mV). c This bar graph summarized the effects of GMQ (10 μM), verruculogen (Verr, 1 μM), or TRAM-34 (1 μM) on the BK_Ca-channel open probability measured at + 60 mV (mean ± S.E.M.; n = 9 for each bar). The addition of 10 μM GMQ significantly increased the probability of channel openings (control vs. GMQ: 0.019 ± 0.004 vs. 0.039 ± 0.007, n = 9/group, p = 0.008), whereas 1 μM verruculogen effectively decreased open BK_Ca channels (control vs. verruculogen: 0.019 ± 0.004 vs. 0.002 ± 0.001, n = 9/group, p = 0.004). d–g Each large current downward deflection, with an amplitude of 3.1 ± 0.1 pA (n = 12), indicated the opening of a single BK_Ca channel. We simultaneously measured the open channel probability (d) and the waveform height (e) of the membrane potential in differentiated AFSCs. Each circled symbol in e indicates detection of the depolarizing waveform. f The probability of channel openings tended to be positively correlated with changes in the amplitude of depolarizing waveforms. The slope between the open channel probability and the waveform height was 0.44. g This graph showed the cross-correlation plot (i.e., correlation coefficient versus time lag) with a time lag of approximate 5.0 ms (indicated by an asterisk). ^*Significantly different from the control (p < 0.05)