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Properties of the delayed rectifier potassium current in porcine sino‐atrial node cells
Author(s) -
Ono Kyoichi,
Shibata Shigehiro,
Iijima Toshihiko
Publication year - 2000
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.1469-7793.2000.00051.x
Subject(s) - depolarization , chemistry , reversal potential , conductance , biophysics , membrane potential , gating , repolarization , electrophysiology , time constant , potassium channel , patch clamp , medicine , receptor , physics , biochemistry , biology , engineering , condensed matter physics , electrical engineering
1 Whole‐cell currents were recorded in single, spontaneously active cells dissociated from porcine sino‐atrial node, and the conductance and gating properties of the delayed rectifier K + current ( I K ) were investigated. 2 The isolated cells exhibited spontaneous action potentials at a rate of 80.5 ± 5.4 min −1 (mean ± s.e.m., n = 11 ). Under Ca 2+ current block, depolarization from ‐40 mV to various potentials activated a time‐dependent outward current ( I K ). The activation curve of I K showed a half‐activation potential (V ½ ) of 20.5 ± 2.1 mV and a slope factor ( S ) of 16.4 ± 1.2 mV ( n = 8 ). 3 As the duration of the depolarizing pulse to either +10 or +60 mV was prolonged, the amplitude of the tail current increased in proportion to that of the activated outward current during depolarization. 4 E4031 (2‐5 μM), a selective blocker for the rapidly activating component of I K ( I K,r ), hardly affected I K , but chromanol 293B, a selective blocker for the slowly activating component ( I K,s ), inhibited I K with an IC 50 of 8.79 μM. 5 The reversal potential of I K was ‐75.2 ± 2.3 mV with 5.4 mM external and 150 mM internal K + . The time courses of activation and deactivation of I K were fitted by the sum of two exponential functions at various potentials. The relationship between the time constants and membrane potential showed a bell‐shaped curve with a peak at around ‐10 mV for both fast and slow components. 6 The results indicate that in porcine sino‐atrial node cells I K is largely derived from I K,s and that I K,s plays a functional role in the slow diastolic depolarization. I K,s may, in part, account for the relatively slower heart rate of pigs than that of rabbit in which I K,r is a functionally dominant component of I K .