Angiotensin II Induces Automatic Activity of the Isolated Guinea Pig Pulmonary Vein Myocardium through Activation of the IP3 Receptor and the Na+-Ca2+ Exchanger

Figures

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  Figure 1. Induction of automatic contractile activity by angiotensin II in pulmonary vein tissue preparations. (A) Typical contractile records on application of 100 nM angiotensin II (a), 1 μM angiotensin II (b), 1 μM angiotensin II in the presence of 10 μM losartan (c), 1 μM angiotensin II in the presence of 10 μM PD123,319 (d) and 1 μM angiotensin II in the presence of 100 nM carvedilol (e); (B) Summarized time course of the frequency of contraction induced by 100 nM angiotensin II (squares), and 1 μM angiotensin II (circles). The 0 min on the time scale indicates the onset of contractile activity. Symbols and vertical bars indicate the mean ± S.E.M. from 4 and 11 experiments, respectively; (C) Summarized results of the rate of induction of automatic contractions. Columns indicate the rate of induction 10 to 17 experiments. Asterisks indicate significant difference from the control (p < 0.05) as evaluated by the Fisher’s exact test.

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  Figure 2. Induction of automatic contractile activity by angiotensin I in pulmonary vein tissue preparations. (A) Typical contractile records on application of 1 μM angiotensin I alone (a), in the presence of 10 μM losartan (b), in the presence of 1 μM captopril (c), in the presence of 10 μM chymostatin (d); (B) Summarized time course of the frequency of contraction induced by 1 μM angiotensin I. The 0 min on the time scale indicates the onset of contractile activity. Symbols and vertical bars indicate the mean ± S.E.M. from 8 experiments; (C) Summarized results of the rate of induction of automatic contractions by angiotensin I. Columns indicate the rate of induction from 15 to 20 experiments. Asterisks indicate significant difference from the control (p < 0.05) as evaluated by the Fisher’s exact test.

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  Figure 3. Effect of angiotensin II on intracellular Ca2+ dynamics in pulmonary vein cardiomyocytes loaded with the Ca2+ sensitive fluoroprobe fluo-4. (A) Typical fluorescence images under quiescence (a), on firing of Ca2+ sparks (b; arrow) and on firing of a Ca2+ transient (c); (B) Time courses of the fluorescence of the entire cell (a, b) and in the circular region of 1 μm in diameter at the site shown by the arrow in Ab (c, d) before (a, c) and after the application of 1 μM angiotensin II (b, d). The time points Aa, Ab and Ac in panel b and d corresponds to the panels a, b and c of A; (C) Summarized results for the rate of induction of Ca2+ transients by angiotensin II. Columns indicate the rate of induction from 14 to 17 experiments. Asterisks indicate statistical significance (p < 0.05) from the control as evaluated by the Fisher’s exact test; (D) Summarized results for the increase in the frequency of Ca2+ spark firing by angiotensin II. Open columns, hatched columns and closed columns indicate the frequency in the absence of agents, after the application of 10 μM losartan or 3 μM xestospongin C, and after further application of 1 μM angiotensin II, respectively. Columns and vertical…

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  Figure 4. Effects of angiotensin II on automatic action potential firing and diastolic depolarization. (A) A typical membrane potential trace on application of 1 μM angiotensin II (a) and an expanded trace after the application showing the oscillation of the membrane potential and diastolic depolarization preceding the action potentials (b); (B) Summarized results for the rate of induction of action potentials by 1 μM angiotensin II alone and in the presence of 0.1–3 μM xestospongin C, 0.1-1 μM SEA0400, 2 μM 2-APB, 2 mM Ni2+, or 0.1 μM ryanodine. Columns indicate the rate of induction from 12 to 14 experiments. Asterisks indicate statistical significance (p < 0.05) from the control as evaluated by the Fisher’s exact test; (C) Typical spontaneous action potential traces before and after the application of 1 μM angiotensin II (a) and an overlay of the diastolic depolarization phase before (black) and after (red) the application (b); (D) Summarized results for the increase in action potential firing frequency by angiotensin II; (E) Summarized results for the increase in the diastolic depolarization slope by angiotensin II. Open and closed columns in D and E indicate the values before and…

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  Figure 5. Enhancement of diastolic depolarization by angiotensin II under constant firing frequency. (A): Typical action potential traces under 1 Hz stimulation in the absence and presence of 1 μM angiotensin II. Arrows indicate field stimulation at 1 Hz; (B) Typical traces of the diastolic depolarization phase before (black) and after (red) the application of 1 μM angiotensin II overlaid for comparison. Angiotensin II was added alone (a) or in the presence of 10 μM losartan (b), 3 μM xestospongin C (c) or 1 μM SEA0400 (d); (C) Summarized results for the angiotensin II-induced changes in the diastolic depolarization slope. Columns and vertical bars indicate the mean ± S.E.M. from 6 experiments. Asterisks indicate statistical significance (p < 0.05) from the control as evaluated by the Dunnett’s test for multiple comparisons.

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  Figure 6. Effect of losartan, xestospongin C and SEA0400 on spontaneous action potentials. (A): Typical traces before and after the application of 10 μM losartan (a) and their diastolic depolarization phase overlaid for comparison (b); (B) Typical traces before and after the application of 3 μM xestospongin C (a) and their diastolic depolarization phase overlaid for comparison (b); (C) Typical traces before and after the application of 1 μM SEA0400 (a) and their diastolic depolarization phase overlaid for comparison (b); (D) Summarized results for the decrease in action potential firing frequency; (E) Summarized results for the decrease in the diastolic depolarization slope. Open and closed columns in D and E indicate the values before and after the addition of agents, respectively. Columns and vertical bars indicate the mean ± S.E.M. from 6 experiments. Asterisks indicate statistical significance (p < 0.05) as evaluated by the paired t-test.