Mechanisms for the α-Adrenoceptor-Mediated Positive Inotropy in Mouse Ventricular Myocardium: Enhancing Effect of Action Potential Prolongation

Figures

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  Figure 1. Effects of pharmacological interventions on the positive inotropic responses to phenylephrine. (A) Typical traces of the positive inotropy induced by phenylephrine in the absence and presence of prazosin, SEA0400, nifedipine, and chelerythrine (CHE). Dots indicate the application of 10 µM phenylephrine. (B) Summarized results for effects of the drugs on the positive inotropy of neonatal mice. Columns and vertical bars indicate the mean ± S.E.M. from 5–6 ventricular preparations. The asterisks indicated significant differences, p < 0.05, from corresponding control values, as evaluated by one-way ANOVA with Dunnett’s test.

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  Figure 2. Effects of phenylephrine on the L-type Ca2+ current and voltage-dependent K+ current. Typical recording of the L-type Ca2+ current (A) and the K+ current (C) in the absence (gray) and presence (black) of 10 µM phenylephrine. The enlarged trace of the time axis was shown as an inset in (C). Current–voltage relationship of the L-type Ca2+ current (B) and the K+ current (D) obtained before (open circles) and after (closed circles) the application of 10 µM phenylephrine and after further application of 1 µM prazosin (gray circles). Symbols and vertical bars indicate the mean ± S.E.M. from 5 cardiomyocytes. The asterisks indicated significant differences, p < 0.05, from corresponding control values, as evaluated by one-way ANOVA with Dunnett’s test.

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  Figure 3. Effects of phenylephrine on the action potential configurations. Typical recording of action potential in the absence (open circle) and the presence (closed circle) of 10 µM phenylephrine.

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  Figure 4. Effect of cromakalim on the phenylephrine-induced action potential duration prolongation and the positive inotropy. (A) Typical action potential recording in the absence (open circle) and presence (closed triangle) of 30 µM cromakalim and after further application of 10 µM phenylephrine (closed circle). (B) Typical traces of the positive inotropy in the absence and presence of 30 µM cromakalim. Dots indicate the application of 10 µM phenylephrine. (C) Summarized results for effects of the drugs on the positive inotropy. Columns and vertical bars indicate the mean ± S.E.M. from 8 ventricular preparations. The asterisk indicates a significant difference, p < 0.05, from corresponding values in control, as evaluated by Student’s t-test.