Potassium-related membrane currents in the bullfrog atrial muscle differentiated in the presence of barium.
Effects of Ba on the potassium-related currents were studied on the bullfrog atrial muscle under voltage clamp with double sucrose-gap techniques. Ba, in a dose over 0.1 mM, abolished the anomalous rectification of the membrane by inhibiting the background current which reversed sign nearly at the K equilibrium potential (IK1). Ba, thus reducing the K-depletion current for hyperpolarizations, revealed the presence of funny inward current (If or Ih) in the proper atrial muscle. An increase in [K]0 increased If, and the current showed a threshold at about -80 mV and was saturated at above -160 mV in 5 mM [K]0. The delayed outward current (Ix) for depolarizations was also depressed by Ba. The depression occurred in a voltage- and time-dependent manner, manifesting an unblocking for stronger depolarizations. An analysis of the current tail, however, disclosed that low concentrations of Ba (up to 0.1 mM) inhibited the accumulation component (Ia) of the current without diminishing the next slow component of Ix (Ixs). The remaining Ixs showed a reversal potential of -82 mV, suggesting that this current is largely carried by potassium ions. These data clearly show that in the presence of Ba, If and Ixs can be differentiated from other membrane currents in the frog atrial muscle.
Goto
M
M
Ikeda
K
K
Umeno
T
T
Mitsuiye
T
T
D000818:Animals; D001001:Anura; D001464:Barium / Q000494:pharmacology*; D001696:Biomechanical Phenomena; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D006325:Heart Atria; D007473:Ion Channels / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism*; D010210:Papillary Muscles / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011930:Reaction Time
D007473:Ion Channels; D001464:Barium; D011188:Potassium