XB-IMG-155615
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Fig 1. Isolation of Ito amplitude and inactivation kinetics.Whole-cell patch-clamp recordings were taken from individual murine cardiomyocytes isolated from the left ventricular free wall. Outward currents were activated by depolarizing voltage pulses from -80 to +40 mV. Inward sodium currents (not shown) were inactivated by a brief (8 ms) prepulse to -50 mV. Voltage protocols are shown below current traces. A. Prepulse-inactivation-subtraction method to isolate Ito in a male wild-type (KChIP2+/+) myocyte. A fraction of current was optionally inactivated by a 160 ms prepulse to -40 mV. Subtraction of the remaining outward current (2) from the compound outward current (obtained without the 160 ms prepulse, 1) yielded a rapidly inactivating current trace (S), referred to as Ito. The inactivation of the Ito trace was fitted by a single-exponential function. B. Compound outward current recorded from the same myocyte as in A during a 5 s voltage pulse to +40 mV (dotted lines represent zero current). For the same current trace the decay was fitted by a double-exponential (2exp, top) and a triple-exponential function (3exp, bottom). The root mean square (RMS) values of the fits are indicated. C. Corresponding RMS2exp and RMS3exp values obtained for 12 male KChIP2+/+ myocytes. RMS3exp values were significantly smaller than RMS2exp values (§, Student's paired t-test); i.e. the triple-exponential fit was more accurate. D. Mean time constants obtained by fitting the decay of isolated Ito traces with a single-exponential function (τs, empty bar) and by fitting the compound outward current decay with a triple-exponential function (τ1, τ2 and τ3, grey bars). Note the close match between τs and τ1. E. Mean peak amplitude of the isolated Ito traces (empty bar) and amplitudes of the individual time constants obtained by triple-exponential fitting (A1, A2 and A3, grey bars). The amplitude of the non-inactivating current component (A0, right grey bar) was obtained by fitting P/n leak-subtracted current traces (not shown). Image published in: Waldschmidt L et al. (2017) © 2017 Waldschmidt et al. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution license Larger Image Printer Friendly View |