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Contribution of Ca 2+ ‐activated K + channels and non‐selective cation channels to membrane potential of pulmonary arterial smooth muscle cells of the rabbit
Author(s) -
Bae Young Min,
Park Myoung Kyu,
Lee Suk Ho,
Ho WonKyung,
Earm Yung E.
Publication year - 1999
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.1469-7793.1999.747ad.x
Subject(s) - hyperpolarization (physics) , extracellular , chemistry , biophysics , membrane potential , reversal potential , depolarization , repolarization , patch clamp , intracellular , charybdotoxin , ouabain , electrophysiology , biochemistry , stereochemistry , medicine , sodium , biology , organic chemistry , receptor , nuclear magnetic resonance spectroscopy
1 Using the perforated patch‐clamp or whole‐cell clamp technique, we investigated the contribution of Ca 2+ ‐activated K + current ( I K(Ca) ) and non‐selective cation currents ( I NSC ) to the membrane potential in small pulmonary arterial smooth muscle cells of the rabbit. 2 The resting membrane potential (V m ) was ‐39·2 ± 0·9 mV ( n = 72 ). It did not stay at a constant level, but hyperpolarized irregularly, showing spontaneous transient hyperpolarizations (STHPs). The mean frequency and amplitude of the STHPs was 5·6 ± 1·1 Hz and ‐7·7 ± 0·7 mV ( n = 12 ), respectively. In the voltage‐clamp mode, spontaneous transient outward currents (STOCs) were recorded with similar frequency and irregularity. 3 Intracellular application of BAPTA or extracellular application of TEA or charybdotoxin suppressed both the STHPs and STOCs. The depletion of intracellular Ca 2+ stores by caffeine or ryanodine, and the removal of extracellular Ca 2+ also abolished STHPs and STOCs. 4 Replacement of extracellular Na + with NMDG + caused hyperpolarization V m of without affecting STHPs. Removal of extracellular Ca 2+ induced a marked depolarization of V m along with the disappearance of STHPs. 5 The ionic nature of the background inward current was identified. The permeability ratio of K + : Cs + : Na + : Li + was 1·7 : 1·3 : 1 : 0·9, indicating that it is a non‐selective cation current ( I NSC ). The reversal potential of this current in control conditions was calculated to be ‐13·9 mV. The current was blocked by millimolar concentrations of extracellular Ca 2+ and Mg 2+ . 6 From these results, it was concluded that (i) hyperpolarizing currents are mainly contributed by Ca 2+ ‐activated K + (K Ca ) channels, and thus STOCs result in transient membrane hyperpolarization, and (ii) depolarizing currents are carried through NSC channels.