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We used the Dynamic Clamp technique for i) comparative validation of conflicting computational models of the hyperpolarization-activated funny current, If, and ii) quantification of the role of If in mediating autonomic modulation of heart rate. Experimental protocols based on the injection of a real-time recalculated synthetic If current in sinoatrial rabbit cells were developed. Preliminary results of experiments mimicking the autonomic modulation of If demonstrated the need for a customization procedure to compensate for cellular heterogeneity. For this reason, we used a cell-specific approach, scaling the maximal conductance of the injected current based on the cell's spontaneous firing rate. The pacemaking rate, which was significantly reduced after application of Ivabradine, was restored by the injection of synthetic current based on the Severi-DiFrancesco formulation, while the injection of synthetic current based on the Maltsev-Lakatta formulation did not produce any significant variation. A positive virtual shift of the If activation curve, mimicking the Isoprenaline effects, led to a significant increase in pacemaking rate (+17.3 ± 6.7%, p

Background: Loss of the rapid delayed rectifier K+ current (IKr) leads to remarkable action potential duration (APD) prolongation and instability (measured by its short term variability; BVR). It is unknown whether APD and its BVR can be separately modulated and which among IKr gating properties is more influential in determining them.Aims: to investigate 1) whether the effects of IKr blockade (by E4031) on APD and BVR are necessarily concordant; 2) the sensitivity of APD and BVR to changes in specific IKr gating parameters.Methods: a numerical IKr model (mIKr) was constructed to fit E4031-sensitive current, previously recorded under AP-clamp conditions in guinea-pig ventricular myocytes. Native IKr was blocked by E4031 and replaced by mIKr under Dynamic-Clamp (DC) conditions. Once established that mIKr was able to fully revert the effect of E4031 on APD and BVR, we tested the effect of negative and positive changes in its gating parameters. Maximal conductance (gmax), mid-potentials activation (V0.5A) and inactivation (V0.5I) and activation/deactivation time-constant (tau) were considered.Results: E4031 increased APD and BVR. mIKr injection restored APD and BVR (NS vs control). Shifts in V0.5I changed APD and BVR concordantly, both being increased for a −15 mV shift and decreased for +15 mV one. On the other hand, a +15 mV shift of V0.5A or a 35% reduction in gmax increased BVR without affecting APD significantly. Changes in tau (±50%), did not affect APD and BVR significantly, but an opposite trend was observed for the two variables.Conclusions: 1) restoration of the control APD and BVR by mIKr indicates that known IKr properties are adequate to account for IKr impact repolarization and its stability; 2) APD and BVR tend to change concordantly but they may be independently affected by changes in gating properties.