摘要Background Few studies have explored the inward sodium current (INa) kinetics of transitional cardiomyocytes.This study aimed to explore the kinetics of transitional cardiomyocytes types α and β.Methods The whole-cell patch clamp technique was used to study the rapid INa of isolated transitional cardiomyocytes in the Koch triangle of rabbit hearts.Results Maximal amplitude and density of INa in type a and type β was (-1627±988) pA (α),(-35.17±6.56) pA/pF (β) and (-3845±467) pA (α),(-65.64±10.23) pA/pF (β) (P<0.05).Steady state activation curves of INa,fitted to a Boltzmann distribution for both types,were sigmoid in shape.Half activation voltage and slope factors did not significantly differ between types at (-43.46±0.85) mV (α),(-41.39±0.47) mV (β) or (9.04±0.66) mV (α),(11.08±0.89) mV (β).Steady state inactivation curves of INa,fitted to a Boltzmann distribution in both types were inverse "S" shape.Half inactivation voltage and slope factors were (-109.9±0.62) mV (α),(-107.5±0.49) mV (β) and (11.78±0.36) mV (α),(11.57±0.27) mV (β),(P>0.05),but time constants of inactivation were significantly different at (1.10±0.19) mV (α) and (2.37±0.33) ms (β),(P<0.05).Time constants of recovery from inactivation of INa for both types were (122.16±27.43) mV (α) and (103.84±28.97) ms (β) (P<0.05).Conclusions Transitional cardiomyocytes in rabbit hearts show a heterogeneous,voltage gated and time dependent fast inward sodium current.Types a and 13 show the features of INa similar to those in slow-and fast-response myocytes,with probably better automaticity and conductivity,respectively.