Sodium current kinetics of transitional myocytes in Koch triangle of rabbit hearts.
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 alpha and beta.


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 alpha and type beta was (-1627 +/- 288) pA (alpha), (-35.17 +/- 6.56) pA/pF (beta) and (-3845 +/- 467) pA (alpha), (-65.64 +/- 10.23) pA/pF (beta) (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 (alpha), (-41.39 +/- 0.47) mV (beta) or (9.04 +/- 0.66) mV (alpha), (11.08 +/- 0.89) mV (beta). 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 (alpha), (-107.5 +/- 0.49) mV (beta) and (11.78 +/- 0.36) mV (alpha), (11.57 +/- 0.27) mV(beta), (P > 0.05), but time constants of inactivation were significantly different at (1.10 +/- 0.19) mV (alpha) and (2.37 +/- 0.33) ms (beta), (P < 0.05). Time constants of recovery from inactivation of INa for both types were (122.16 +/- 27.43) mV (alpha) and (103.84 +/- 28.97) ms (beta) (P < 0.05).


CONCLUSIONS
Transitional cardiomyocytes in rabbit hearts show a heterogeneous, voltage gated and time dependent fast inward sodium current. Types alpha and beta show the features of INa similar to those in slow- and fast-response myocytes, with probably better automaticity and conductivity, respectively.
Ren
Fu-xian
FX
Department of Cardiology, Second Hospital, Xi'an Jiaotong University, Xi'an, Shaanxi 710004, China.
Niu
Xiao-lin
XL
Ou
Yan
Y
Xie
Song-mei
SM
Ling
Feng-dong
FD
Zhou
Shi-sheng
SS
Li
Ya-jie
YJ
D000818:Animals; D005260:Female; D015640:Ion Channel Gating; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D032383:Myocytes, Cardiac / Q000378:metabolism*; D011817:Rabbits; D015222:Sodium Channels / Q000502:physiology*
D015222:Sodium Channels