title: Membrane proteins involved in potassium shifts during muscle activity and fatigue.
abstract: Muscle activity is associated with potassium displacements, which may cause fatigue. It was reported previously that the density of the large-conductance Ca2+-dependent K+ (BK(Ca)) channel is higher in the T tubule membrane than in the sarcolemmal membrane and that the opposite is the case for the ATP-sensitive K+ (K(ATP)) channel. In the present experiments, we investigated the subcellular localizations of the strong inward rectifier 2.1 K+ (Kir2.1) channel and the Na+-K+-2Cl- (NKCC)1 cotransporter with Western blot analysis of different muscle fractions. Furthermore, muscle function was studied while trying to manipulate the opening probability or transport capacity of these proteins during electrical stimulation of isolated soleus muscles. All experiments were made with excised muscle from male Wistar rats. Kir2.1 channels were almost undetectable in the sarcolemmal membrane but present in the T tubule membrane, whereas NKCC1 cotransporters were present in the sarcolemmal membrane. For muscles incubated in a buffer containing pinacidil, NS1619, Ba2+, or bumetanide, there was a faster reduction in peak force (P < 0.05). Furthermore, bumetanide incubation reduced the peak force at the onset of electrical stimulation (P < 0.05). Thus the effects on muscle force indicate that these drugs can affect K+-transporting proteins and thereby influence K+ accumulation, especially in the T tubules, suggesting that K(ATP) and BK(Ca) channels are responsible for K+ release and decrease in force during repeated muscle contractions, whereas Kir2.1 and NKCC1 may have a role in K+ reuptake.
authors.affiliation: Copenhagen Muscle Research Centre, Institute of Molecular Biology and Physiology, August Krogh Bldg., DK-2100 Copenhagen Ø, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Kristensen
authors.forename: Thomas
authors.initials: T
authors.lastname: Hansen
authors.forename: Carsten
authors.initials: C
authors.lastname: Juel
mesh_terms: D000818:Animals; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008297:Male; D008565:Membrane Proteins / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D028021:Sodium-Potassium-Chloride Symporters / Q000502:physiology*; D064506:Solute Carrier Family 12, Member 2; D013314:Stress, Mechanical; D014018:Tissue Distribution
chemical_list: C494842:Kcnma1 protein, rat; C489461:Kir2.1 channel; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008565:Membrane Proteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; C578879:Slc12a2 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D011188:Potassium