Pharmacological unloading prevents contracture, improves viability and function in an ischemia-reperfusion model using porcine, rabbit and primate cardiac slices

Background Reperfusion after warm or cold myocardial ischaemia can trigger early irreversible contracture, causing acute mechanical failure and prolonged dysfunction. Here, we suggest using living cardiac slice culture as an ischaemia-reperfusion model to enable testing of early-window cardioprotective strategies. Purpose To explore whether transient pharmacological contractile unloading prevents acute contracture and preserves long-term electromechanical function in living myocardium subjected to warm and cold ischaemia. Methods After warm and cold ischaemia, left-ventricular slices of 300 µm thickness were mounted in biomimetic culture chambers with preload and electrical pacing. At culture initiation, slices were treated with a combination of mavacamten (Mava), cytochalasin D (CytoD) and 2,3-butanedione monoxime (BDM) or vehicle as control for 2 h, followed by complete washout and drug-free culture. Porcine cohort (slices/hearts): 11/7 control vs 16/10 combination; 2 h diastolic tension and post-washout twitch force were quantified. Rabbit cohort: 13/4 control, 40/6 BDM, 36/4 BDM+CytoD, 36/5 BDM+CytoD+Mava. Baboon cohort: 2 healthy donors (16 slices total) cultured up to 3 weeks; longitudinal force/diastolic tension, force–frequency response, post-pause potentiation and connexin-43 lateralisation were assessed. Results In pig myocardium, which was exposed to 10 min of warm and 5 h of cold ischaemia, untreated slices developed a marked contracture, indicated by a diastolic tension surge at 2 h (16210 ± 1064 µN), with absent twitch force after washout (0 µN). Pharmacological contractile unloading attenuated 2 h diastolic tension (7099 ± 1188 µN; 56% lower), elicited post-washout mechanical activity (twitch force: 337 ± 66 µN) and enabled a regular response to electrical stimulation typically persisted for up to 7 days. In rabbit (5 min warm and 3–4 h cold ischaemia), control slices developed irreversible contracture (14510 ± 1720 µN) and never responded to electrical stimulation. Adding BDM (9419 ± 1120 µN) and BDM+CytoD (4138 ± 550 µN) reduced contracture significantly, while BDM+CytoD+Mava even caused slight relaxation (-1463 ± 182 µN). In baboon (5 min warm and 3 h cold ischaemia), the same protocol showed directionally consistent preservation of electromechanical reserve versus control, including lower diastolic tension, a more positive force–frequency relationship with improved contractile reserve, increased post-pause potentiation and reduced Cx43 lateralisation after long-term culture. Conclusion A brief period of pharmacological unloading via myofilament–cytoskeletal contractile-silencing may prevent contracture, preserve long-term function and stabilise structural features in rabbit, pig and primate myocardium. These cross-species findings support pharmacological unloading as a post-conditioning strategy with potential relevance for heart transplantation or myocardial ischaemia.