Free energy of ATP-hydrolysis fails to affect ATP-dependent potassium channels in isolated mouse ventricular cells.
The single channel recording technique has been used to study the adenosine-5'-triphosphate (ATP)-dependent K+ channel in isolated mouse ventricular cells. The aim of this work was to determine if the activity of the K+ channel depends on the free energy of ATP-hydrolytic reaction (phosphorylation potential) in addition to the well-studied direct block by ATP. When the phosphorylation potential was changed from 60 to 50, to 40 and back to 60 kJ/mol at a constant ATP-concentration of 10(-4) mol/l, the ATP-channel activity showed a run down that is best described by a linear function. Changing the ATP-concentration of the bath solution from 0.01 to 1 and back to 0.01 mmol/l by a factor of 10 at a constant phosphorylation potential of 50 kJ/mol, resulted in a run down of the mean average current by a reduction of the open state probability in a concentration dependent manner. A dissociation constant of about 0.14 mmol/l could be estimated. The amplitude of the single channel current was not affected by ATP-concentrations in contrast to changes in phosphorylation potential. A significant increase in the single channel current accompanying a decrease in the phosphorylation potential at constant ATP concentrations was observed. This effect might be due to a decrease of free Mg2(+)-concentration by an increase of the ADP concentration in solutions with lower phosphorylation potentials. An allosteric regulation of the ATP-dependent K+ channel dependent on the free ATP concentration together with the Mg2(+)-ADP concentration seems to be a more likely explanation than regulation by phosphorylation/dephosphorylation secondary to a breakdown of ATP.
Albitz
R
R
Julius Bernstein Institute of Physiology, Martin Luther University, Halle, German Democratic Republic.
Kammermeier
H
H
Nilius
B
B
D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D006352:Heart Ventricles; D006868:Hydrolysis; D015640:Ion Channel Gating / Q000187:drug effects*; D051379:Mice; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D013816:Thermodynamics
D015221:Potassium Channels; D000255:Adenosine Triphosphate; D011188:Potassium