Direct inhibition of the pancreatic beta-cell ATP-regulated potassium channel by alpha-ketoisocaproate.
The ATP-regulated potassium (KATP) channel plays an essential role in the control of insulin release from the pancreatic beta-cell. In the present study we have used the patch-clamp technique to study the direct effects of alpha-ketoisocaproate on the KATP channel in isolated patches and intact pancreatic beta-cells. In excised inside-out patches, the activity of the KATP channel was dose-dependently inhibited by alpha-ketoisocaproate, half-maximal concentration being approximately 8 mM. The blocking effect of alpha-ketoisocaproate was fully reversible. Stimulation of channel activity by the addition of ATP/ADP (ratio 1) did not counteract the inhibitory effect of alpha-ketoisocaproate. In the presence of the metabolic inhibitor sodium azide, alpha-ketoisocaproate was still able to inhibit single channel activity in excised patches and to block whole cell KATP currents in intact cells. No effect of alpha-ketoisocaproate could be obtained on either the large or the small conductance Ca2+-regulated K+ channel. Enzymatic treatment of the patches with trypsin prevented the inhibitory effect of alpha-ketoisocaproate. Based on these observations, it is unlikely that the blocking effect of alpha-ketoisocaproate is due to an unspecific effect on K+ channel pores. Leucine, the precursor of alpha-ketoisocaproate, did not affect KATP channel activity in excised patches. Our findings are compatible with the view that alpha-ketoisocaproate not only affects the beta-cell stimulus secretion coupling by generation of ATP but also by direct inhibition of the KATP channel.
Bränström
R
R
Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, S-171 76 Stockholm, Sweden.
Efendić
S
S
Berggren
P O
PO
Larsson
O
O
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004594:Electrophysiology; D005260:Female; D007515:Islets of Langerhans / Q000502:physiology*; D007651:Keto Acids / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D051379:Mice; D008820:Mice, Obese; D015394:Molecular Structure; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D019810:Sodium Azide / Q000494:pharmacology; D014357:Trypsin / Q000378:metabolism
D007651:Keto Acids; D026902:Potassium Channel Blockers; C015963:2-ketopentanoic acid; C013082:alpha-ketoisocaproic acid; D000255:Adenosine Triphosphate; D019810:Sodium Azide; D014357:Trypsin