Phosphodiesterases 3 and 4 Differentially Regulate the Funny Current, If, in Mouse Sinoatrial Node Myocytes

Figures

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  Figure 1. General PDE inhibition activates If in SAMs at rest via a PKA-independent mechanism. (A,B) Average (±SEM) normalized conductance-voltage plots for If in control (black), IBMX (100 µM in extracellular solution; red), PKI (10 µM in patch pipette; grey), or IBMX plus PKI (dark red). Numbers in parentheses in the legends indicate the number of cells in each dataset. Insets show representative If current families. Red traces show currents elicited by voltage steps to −120 mV to illustrate shifts in voltage dependence. Scale bars, 200 pA, 500 ms; and (C) average (±SEM) V1/2 for If for the indicated conditions. Asterisks indicate p < 0.05 versus control; one-way ANOVA with Holm-Sidak post-test.

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  Figure 2. PDE4 inhibition activates If in SAMs at rest via a PKA-independent mechanism. (A,B) Average (±SEM) normalized conductance-voltage plots for If in control (black), rolipram (10 µM in the extracellular solution; green), PKI (10 µM in the patch pipette; grey), or PKI plus rolipram (dark green). Numbers in parentheses in the legends indicate the number of cells in each dataset. Insets show representative If current families. Red traces elicited by voltage steps to −120 mV illustrate shifts in the voltage dependence. Scale bars, 100 pA, 500 ms. for control, 500 pA, 500 ms for PKI; and (C) shows the average (±SEM) V1/2 for If for indicated conditions. Asterisks indicate p < 0.05 versus control; one-way ANOVA with Holm-Sidak post-test.

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  Figure 3. Effects of PDE3 inhibition on If at rest. (A,B) Average (±SEM) normalized conductance-voltage plots for If in control (black), milrinone (50 µM in the extracellular solution; blue), PKI (10 µM in the patch pipette; grey), or milrinone plus PKI (dark blue). Numbers in parentheses in the legends indicate the number of cells in each dataset. Insets show representative If current families. Red traces elicited by voltage steps to −120 mV illustrate shifts in the voltage dependence. Scale bars, 100 pA, 500 ms for control, 500 pA, 500 ms for PKI; and (C) shows the average (±SEM) V1/2 for If for indicated conditions. Asterisk indicates p < 0.05 versus control; one-way ANOVA with Holm-Sidak post-test.

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  Figure 4. Effects of PDE inhibition on the ability of ISO to shift the voltage-dependence of If. The shift in V1/2 of If in response to ISO (ΔV1/2-ISO) was determined for individual cells by measuring V1/2 values before and after wash-on of ISO in (A) control Tyrode’s extracellular solution (black) or Tyrode’s solution with PKI (10 µM) in the patch pipette (grey); (B) IBMX (100 µM in the extracellular solution; red) or IBMX with PKI in the pipette (dark red); (C) rolipram (10 µM in the extracellular solution; light green) or rolipram with PKI in the pipette (dark green); and (D) milrinone (50 µM; blue) or milrinone with PKI in the pipette (dark blue). Dashed lines indicate the ΔV1/2-ISO shift in control conditions for comparison. Asterisks indicate p < 0.05 compared to the corresponding condition without PKI; t-tests. Double daggers indicate a significant shift in response to ISO (p < 0.05 versus a hypothetical shift of 0 mV; one-sample t-tests). Insets represent the hyperpolarization-activated currents elicited by single voltage steps to near the midpoint activation voltage for each condition from individual cells before (black) and after (red) wash-on of ISO in the absence (left) or…