Selective Inhibition of Pulmonary Vein Excitability by Constitutively Active GIRK Channels Blockade in Rats

Figures

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  Figure 1. Effects of 10−7 M acetylcholine (ACh) and 150 nM tertiapin-Q (TQ) on electrically evoked (5 Hz) action potentials recorded simultaneously in the LA wall (LA) and the pulmonary vein (PV) of the same preparation. Pairs of individual traces (a–c) are from a continuous recording obtained under basal conditions (a), then during ACh superfusion (b), and finally in the presence of ACh with the addition of tertiapin-Q (c). (d,e) represent the results obtained from individual microelectrode penetrations in the LA and PV of five preparations, respectively. Squares represent diastolic membrane potential (DMP); circles represent action potential peak values (AP peak). Open symbols represent mean values. SEM are not visible on the figure because they are smaller than the symbols.

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  Figure 2. Effects of 150 nM tertiapin-Q (TQ) on electrically evoked (5 Hz) action potentials recorded simultaneously by intracellular microelectrodes placed in the LA wall (LA) and the pulmonary vein (PV) of the same preparation. Pairs of individual traces (a,b) are from a continuous recording obtained from one preparation under basal conditions (a), then during the superfusion of tertiapin-Q (b). (c,d) represent the results obtained from individual microelectrode penetrations in the PV and LA of ten preparations, respectively. Squares represent diastolic membrane potential (DMP); circles represent action potential peak values (AP peak). Open symbols represent mean values. SEM are not visible on the figure because they are smaller than the symbols.

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  Figure 3. Concentration-dependent effects of acetylcholine (ACh) upon electrically evoked (5 Hz) action potentials in the PV and LA in the continuous presence of 150 nM tertiapin-Q (TQ). Traces are from a continuous recording obtained from one preparation in the PV (a) and LA (b). Data points linked by lines represent the results obtained from individual microelectrode penetrations in the PV (c) and LA (d) of 7 different preparations. Squares represent diastolic membrane potential (DMP); circles represent action potential peak values (AP peak). The mean and SEM values of the data are shown in Table 1.

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  Figure 4. Recovery of over-shooting action potentials in the pulmonary vein (PV) by activation of Kir6.2 (KATP) channels with the pinacidil analog P1075 in the presence of tertiapin-Q (TQ). Electrically evoked (5 Hz) action potentials simultaneously recorded by intracellular microelectrodes placed in the LA wall (LA) and the PV. The pairs of individual traces are from a continuous recording in the PV (a) and the LA (b) in the presence of first 150 nM tertiapin-Q, then following the addition of 30 µM P1075. (c,d). Data points linked by lines represent the results obtained from individual microelectrode penetrations in the PV (c) and LA (d) of seven different preparations, respectively. Squares represent diastolic membrane potential (DMP); circles represent action potential peak values (AP peak). Open symbols represent mean values. SEM are not visible on the figure because they are smaller than the symbols.

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  Figure 5. Comparison of the effects of iberiotoxin (IBTX), VU591, and tertiapin-Q (TQ) upon the quiescent membrane potential of cardiac muscle in the pulmonary vein (PV) of the rat. (a) Representative experiment comparing the effects of first iberiotoxin and then tertiapin-Q on the quiescent membrane potential (QMP). Data values for QMP were obtained by analyzing the otherwise continuous recording every second. The protocol consisted of that developed by Doisne et al. [27], where penetration of cardiac muscle in the PV was performed during 5 Hz electrical stimulation showing over-shooting action potentials. Electrical stimulation then ceased, and the preparation was allowed 10–15 min to establish an approximately steady-state QMP. In this example 10 min of superfusion of iberiotoxin was followed by 10 min superfusion of tertiapin-Q, as indicated by the bars above the recording. Columns and bars graphs represent mean and SEM values of QMP from 5 experiments comparing the effects of iberiotoxin and tertiapin-Q (b) and from 4 experiments comparing the effect of VU591 and tertiapin-Q (c).

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  Figure 6. Tertiapin-Q (300 nM) sensitive currents in isolated left atria (black trace) and pulmonary vein cardiomyocytes (red trace) recorded under control condition in the absence of acetylcholine. Data are expressed as the means of voltage ramp obtained from 8 LA and 10 PV cardiomyocytes. For clarity, vertical bars representing SEM are not included for all data points.

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  Figure 7. GIRK1 and GIRK4 subunits expression in the left atria (LA) and pulmonary vein (PV) cardiomyocytes. (a) Representative western blots of GIRK1 and GIRK4 in LA and PV cardiomyocytes. Bar graphs represent GIRK1 (b) and GIRK4 expression (c) in the PV relative to that in the LA. Data expressed as mean values ± SEM (n = 3, 2 rats/sample).