The gating of nucleotide-sensitive K+ channels in insulin-secreting cells can be modulated by changes in the ratio ATP4-/ADP3- and by nonhydrolyzable derivatives of both ATP and ADP.
The 31P-NMR technique has been used to assess the intracellular ratios and concentrations of mobile ATP and ADP and the intracellular pH in an insulin-secreting cell line, RINm5F. The single-channel current-recording technique has been used to investigate the effects of changes in the concentrations of ATP and ADP on the gating of nucleotide-dependent K+ channels. Adding ATP to the membrane inside closes these channels. However, in the continued presence of ATP adding ADP invariably leads to the reactivation of ATP-inhibited K+ channels, even at ATP4-/ADP3- concentration ratios greater than 7:1. Interactions between ATP4- and ADP3- seem competitive. An increase in the concentration ratio ATP4-/ADP3- consistently evoked a decrease in the open-state probability of K+ channels; conversely, a decrease in ATP4-/ADP3- increased the frequency of K+ channel opening events. Channel gating was also influenced by changes in the absolute concentrations of ATP4- and ADP3-, at constant free concentration ratios. ADP-evoked stimulation of ATP-inhibited channels did not result from phosphorylation of the channel, as ADP-beta-S, a nonhydrolyzable analog of ADP, not only stimulated but enhanced ADP-induced activation of K+ channels, in the presence of ATP. Similarly, ADP was able to activate K+ channels in the presence of two nonhydrolyzable derivatives of ATP, AMP-PNP and beta gamma methylene ATP.
Dunne
M J
MJ
M.R.C. Secretory Control Research Group, University of Liverpool, England.
West-Jordan
J A
JA
Abraham
R J
RJ
Edwards
R H
RH
Petersen
O H
OH
D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000502:physiology*; D002460:Cell Line; D005985:Glyceraldehyde / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000032:analysis / Q000187:drug effects* / Q000648:ultrastructure; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008564:Membrane Potentials / Q000187:drug effects; D009711:Nucleotides / Q000032:analysis / Q000494:pharmacology*; D010766:Phosphorylation; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D013873:Thionucleotides / Q000494:pharmacology
D007328:Insulin; D009711:Nucleotides; D015221:Potassium Channels; D013873:Thionucleotides; C030812:adenosine 5'-O-(2-thiodiphosphate); D005985:Glyceraldehyde; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate