Gating kinetics of potassium channel and effects of nerve growth factors in PC12 cells analyzed with fractal model

AIM: To study the gating kinetics of voltage-dependent K+ channels in clona l pheochromocytoma (PC12) cells and the effect of nerve growth factor (NGF) on it. METHODS: Outward currents of K+ channel were recorded in PC12 cells cultured with or without NGF using cell-attached patch-clamp technique. Th e kinetic features of K+ channel and the effect of NGF on them were analyze d based on the fractal model. RESULTS: The fractal dimension D for the clos ed durations of K+ channel in PC12 cells cultured without NGF was proportio nal to the absolute value of the pipette potential (V-p). Whereas the fract al dimension D' was inversely proportional to it. Under pipette potentials of 0, -30, - 50, and - 70 mV, the values of D were 1.75, 1.88, 1.95, and 2; and of D' were 1.51, 1.40, 1.34, and 1.23. After the addition of NGF the c hanges in the fractal dimensions became more complex. At the same pipette p otential, fractal dimensions for K+ channel in PC12 cells cultured with NGF for both the open and closed durations were not greater than those in PC12 cells cultured without NGF. The kinetic setpoints for both the close and o pen durations did not vary with the pipette potential with values as follow s: A(without NGF) = 0.29 +/- 0.05, A(with NGF) = 0.71 +/- 0. 06, A' (withou t NGF) = 0.110 +/- 0.020, and A' (with NGF) = 0.38 +/- 0.08. CONCLUSION: Th e voltage dependence of D(without NGF) increases the probability of the cha nnel for remaining closed for long durations as the patch is depolarized, a nd that of D'(without NGF) decreases the probability of the channel for rem aining open for long durations as the patch is depolarized. The addition of NGF in the PC12 cell culture accelerates the dynamic process of the K+ cha nnel occurring over long time scales.