Excitation of model ventricular myocytes by stretch-activated currents

A combined experimental and computer model of a cardiac myocyte was used to study the interaction between currents from stretch-activated ion channels (SACs) and other membrane currents, specially sodium (I_Na) and potassium (I_kl), in determining cardiac excitation. Experimentally observes currents activated either by voltage or stretch were simulated based on a myocyte model, a modified Ebihara-Johnson model. Charge threshold for activation by stretch was measured as functions of timing within the cardiac cycle and baseline potassium conductance, g_kl. Model simulations approximated real voltage clamp behaviours and action potentials triggered by currents from SACs. The model predicted that (1) peak I_Na of the stretch-induced impulse showed a parabolic relation to baseline g_Kl with the maximum I_Na of 60% (relative to control level) occurring at a g_Kl of 0.03 mS/cm², and (2) charge threshold was inversely related to g _Kl, regardless of stretch coupling interval. The authors´ results showed that reducing g_kl had contrasting effects on stretch-induced activation of model myocytes: it increased their likelihood for a given stretch magnitude but reduced their tendency to generate depressed action potentials