Effects of Microgravity on Action Potential Wave Propagation in Rat Transmural Ventricle Tissue

Experiments mimicking microgravity condition have multiple effects on cardiac electrophysiology. Therefore, based on experimental data of rats with 2-weeks (short term) and 4-weeks (long term) tail suspension, effect of microgravity on action potentials (APs) were simulated by decreasing $I_{CaL}$ and increasing $I_{NaK}$ based on rat endocardial and epicardial models. Additionally, a 1D model was constructed by considering the increasing of connexin 43 under microgravity condition. Simulation results show that $I_{CaL}$ and $I_{NaK}$ changes have similar effect in reducing APD90 under short term condition, while the inhibition of $I_{CaL}$ is the main factor in reducing APD90 under long term condition. The simulated pseudo-ECG in both conditions showed a shortened QT interval and depressed of ST phase and $T$ wave as experimental observations. Increased expression of connexin 43 in microgravity condition resulted in a mild increase in conduction velocity. Meanwhile, the vulnerable window in 1D ventricle strand reduced in microgravity condition. Compared with short term microgravity condition, all these changes were more prominent in the long term microgravity condition. In conclusion, this study provides new insight into understanding of impaired cardiac functions in short and long term microgravity conditions during spaceflight.