Arf-1 (ADP-ribosylation factor-1) is involved in the activation of a mammalian Na+-selective current.
Stimulation of mammalian cells often results in an increase in the intracellular Na(+) concentration, brought about by Na(+) influx into the cell via Na(+)-permeable ion channels. In some cell types, particularly renal epithelia and mast cells, non-hydrolysable analogues of GTP, such as GTP[S] (guanosine 5'-[gamma-thio]triphosphate), activate a non-voltage-activated Na(+)-selective current. We have carried out whole-cell patch-clamp experiments to examine how GTP[S] activates the Na(+) current in a rat mast cell line. The ability of GTP[S] to activate Na(+) influx was prevented by including GTP in the pipette solution, indicating the involvement of small G-proteins. Brefeldin A and Arf-1-(2-17), inhibitors of Arf-1 (ADP-ribosylation factor-1) proteins, suppressed the activation of Na(+) entry by GTP[S]. However, non-active succinylated Arf-1-(2-17) or an N-terminal myristoylated peptide directed towards Arf-5 were ineffective. Arf proteins modulate the cytoskeleton, and disruption of the cytoskeleton with cytochalasin D or its stabilization with phalloidin impaired the development of the Na(+) current. Disaggregation of microtubules was without effect. Dialysis with cAMP or inhibition of cAMP phosphodiesterase with caffeine both decreased the extent of Na(+) entry, and this was not prevented by pre-treatment with broad-spectrum protein kinase inhibitors. Collectively, our results suggest that the mechanism of activation of a mammalian non-voltage-activated Na(+)-selective current requires an Arf small G-protein, most probably Arf-1.
Straube
Sebastian
S
Laboratory of Cellular and Molecular Signalling, Department of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
Parekh
Anant B
AB
D020823:ADP-Ribosylation Factor 1 / Q000502:physiology*; D008841:Actin Cytoskeleton / Q000502:physiology; D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000494:pharmacology; D004553:Electric Conductivity; D015640:Ion Channel Gating; D008407:Mast Cells / Q000201:enzymology / Q000502:physiology; D020559:Monomeric GTP-Binding Proteins / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D015222:Sodium Channels / Q000378:metabolism*
D015222:Sodium Channels; D000242:Cyclic AMP; D020823:ADP-Ribosylation Factor 1; D020559:Monomeric GTP-Binding Proteins