Role of stretch-activated channels on the stretch-induced changes of rat atrial myocytes

The role of stretch-activated channels (SACs) on the stretch-induced changes of rat atrial myocytes was studied using a computer model that incorporated various ion channels and transporters including SACs. A relationship between the extent of the stretch and the activation of SACs was formulated in the model based on experimental findings to reproduce changes in electrical activity and Ca2+ transients by stretch. Action potentials (APs) were significantly changed by the activation of SACs in the model simulation. The duration of the APs decreased at the initial fast phase and increased at the late slow phase of repolarisation. The resting membrane potential was depolarised from −82 to −70 mV. The Ca2+ transients were also affected. A prolonged activation of SACs in the model gradually increased the amplitude of the Ca2+ transients. The removal of Ca2+ permeability through SACs, however, had little effect on the stretch-induced changes in electrical activity and Ca2+ transients in the control condition. In contrast, the removal of the Na+ permeability nearly abolished these stretch-induced changes. Plotting the peaks of the Ca2+ transients during the activation of the SACs along a time axis revealed that they follow the time course of the Nai+ concentration. The Ca2+ transients were not changed when the Nai+ concentration was fixed to a control value (5.4 mM). These results predicted by the model suggest that the influx of Na+ rather than Ca2+ through SACs is more crucial to the generation of stretch-induced changes in the electrical activity and associated Ca2+ transients of rat atrial myocytes.