Effects of ras and Rap1 on electrical excitability of differentiated NG108-15 cells.
Effects of two small G-proteins, Rap1 and Ras, on the sodium channel activity in NG108-15 cells were studied using sindbis virus-mediated gene transfer. When an activated Rap1A mutant (Rap1-12V, the activated mutant of Rap1 carrying glycine to valine substitution at codon 12) or a dominant-negative H-Ras mutant (Ras-17N, carrying serine to asparagine substitution at codon 17) was expressed in differentiated NG108-15 cells, the proportion of cells generating action potential decreased and the amplitudes of sodium current diminished. This effect was sensitive to an inhibitor of protein kinase A. The effects of a cyclic AMP (cAMP) analog (dibutyl cAMP) on sodium current in these cells were biphasic: inhibitory at lower concentrations (<100 microM) and enhancing at higher concentrations (200-500 microM). The inhibitory phase of cAMP effect was suppressed by an activated Ras mutant (Ras-12V) while the enhancing phase was suppressed by Rap1-12V. These data are consistent with the model that Rap1 and Ras function as counteracting regulators of voltage-gated sodium current through cAMP-dependent mechanisms.
Department of Molecular Oncology, Kyoto University Graduate School of Medicine, Yoshida, Konoe-cho, Sakyo-Ku, Kyoto 606-8501, Japan.
Y
Y
Imamura
N
N
Matsumoto
S
S
Kondo
H
H
Kitayama
M
M
Noda
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D045744:Cell Line, Tumor; D051379:Mice; D020827:rap1 GTP-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D018631:ras Proteins / Q000096:biosynthesis* / Q000235:genetics
D020827:rap1 GTP-Binding Proteins; D018631:ras Proteins