Tolerance for ATP-insensitive K(ATP) channels in transgenic mice.
To examine the role of sarcolemmal K(ATP) channels in cardiac function, we generated transgenic mice expressing GFP-tagged Kir6.2 subunits with reduced ATP sensitivity under control of the cardiac alpha-myosin heavy chain promoter. Four founder mice were isolated, and both founders and progeny were all apparently normal and fertile. Electrocardiograms from conscious animals also appeared normal, although mean 24-hour heart rate was approximately 10% lower in transgenic animals compared with littermate controls. In excised membrane patches, K(ATP) channels were very insensitive to inhibitory ATP: mean K(1/2) ([ATP] causing half-maximal inhibition) was 2.7 mmol/L in high-expressing line 4 myocytes, compared with 51 micromol/L in littermate control myocytes. Counterintuitively, K(ATP) channel density was approximately 4-fold lower in transgenic membrane patches than in control. This reduction of total K(ATP) conductance was confirmed in whole-cell voltage-clamp conditions, in which K(ATP) was activated by metabolic inhibition. K(ATP) conductance was not obvious after break-in of either control or transgenic myocytes, and there was no action potential shortening in transgenic myocytes. In marked contrast to the effects of expression of similar transgenes in pancreatic beta-cells, these experiments demonstrate a profound tolerance for reduced ATP sensitivity of cardiac K(ATP) channels and highlight differential effects of channel activity in the electrical activity of the 2 tissues.
Koster
J C
JC
Department of Cell Biology, Washington University School of Medicine, St Louis, MO, USA.
Knopp
A
A
Flagg
T P
TP
Markova
K P
KP
Sha
Q
Q
Enkvetchakul
D
D
Betsuyaku
T
T
Yamada
K A
KA
Nichols
C G
CG
D000200:Action Potentials; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D004553:Electric Conductivity; D004562:Electrocardiography; D049452:Green Fluorescent Proteins; D006321:Heart / Q000502:physiology*; D007202:Indicators and Reagents / Q000378:metabolism; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D009154:Mutation; D009206:Myocardium / Q000166:cytology; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000235:genetics* / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D012508:Sarcolemma / Q000502:physiology
D007202:Indicators and Reagents; D008164:Luminescent Proteins; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D049452:Green Fluorescent Proteins; D000255:Adenosine Triphosphate