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Selective Enhancement of the Slow Component of Delayed Rectifier K + Current in Guinea‐Pig Atrial Cells by External ATP
Author(s) -
Matsimra Hiroshi,
Ehara Tsuguhisa
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.045bi.x
Subject(s) - depolarization , chemistry , conductance , biophysics , patch clamp , electrophysiology , repolarization , analytical chemistry (journal) , physics , medicine , biology , condensed matter physics , chromatography
1 The effects of external ATP on the rapidly and slowly activating components ( I Kr and I Kg , respectively) of the delayed rectifier K + current ( I K ) in guinea‐pig atrial myocytes were determined using the whole‐cell configuration of the patch‐clamp technique. 2 An envelope of tails test was conducted by applying depolarizing pulses to +40 mV from a holding potential of −40 mV for various durations between 50 ms and 2 s under control conditions and during exposure to 50 μM ATP. The ATP‐induced I K , obtained by digital subtraction, exhibited a constant ratio (0.37) of the tail current to time‐dependent current, regardless of the pulse duration. This current ratio was compatible with the predicted ratio of the driving force at +40 and −40 mV for a non‐rectifying K + conductance, suggesting that the ATP‐induced I K is due primarily to I Ks . 3 The amplitude of I Kr isolated from the I K enhanced by ATP, determined as an E‐4031 (5 μM)‐sensitive current, was similar to the control magnitude of I Kr , thus showing that external ATP did not cause an increase in I Kr . 4 The voltage‐dependent activation of the ATP‐induced I K during 500 ms depolarizing test pulses could be described by a Boltzmann equation with a half‐activation voltage ( V 1/2 ) of 11.5 mV and slope factor ( k ) of 12.0 mV, which were close to those of I Kg (V 1/4 of 12.1 mV and k of 12.3 mV), determined as an E‐4031‐resistant I K , under the same isochronal (500 ms) activation conditions. 5 These results provide evidence to suggest that extracellular ATP selectively potentiates the slow component of I K ( I Kg ), with no measurable effects on I Kr , in guinea‐pig atrial myocytes.