Figure 2.
Experimental protocol for measurements of cardiac restitution using a dynamic pacing protocol in contracting and contraction-inhibited hearts uncoupled with Blebbistatin. (A) Measurement pre- and post-Blebbistatin in the same heart (total N = 10 hearts). Pacing from fp = 2.0 to fp = 10.0 Hz with progressively decreasing step size. After the first restitution measurement in the contracting heart, Blebbistatin was added at concentrations of up to 2.8μM. After 20–45 min, when Blebbistatin typically had suppressed all contractile motion, the second restitution measurement was performed in the contraction-inhibited heart. The reversal of the effect of Blebbistatin was verified in a washout experiment (after 1 h). (B) Subsequent increase of Blebbistatin concentration (0.0, 0.7, …, 2.8μM). The restitution measurement from (A) was performed for baseline and then repeated for all four concentrations in the same heart. The concentration was immediately increased after the previous measurement, and the next measurement was started after 30 min.