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Long‐term induction of a unique Cl − current by endothelin‐1 in an epithelial cell line from rat lung: evidence for regulation of cytoplasmic calcium
Author(s) -
Mair Norbert,
Frick Manfred,
Meraner Andreas,
Schramek Herbert,
Dietl Paul
Publication year - 1998
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.1469-7793.1998.055bi.x
Subject(s) - lung , cytoplasm , calcium , endothelin 1 , line (geometry) , term (time) , endothelin receptor , chemistry , microbiology and biotechnology , medicine , endocrinology , biology , physics , geometry , mathematics , quantum mechanics , receptor
1 Using conventional microelectrodes, the perforated patch clamp technique and fluorescence microscopy with fura‐2, we investigated the relationship between the cell membrane potential, whole‐cell currents and the free cytoplasmic Ca 2+ concentration ([Ca 2+ ] i ) in response to 10 nM endothelin‐1 (ET) in a rat respiratory epithelial cell line (L2). 2 Microelectrode experiments revealed that ET caused an immediate depolarization of the cell membrane potential ( V m ) by 25 mV, which was unaffected by Na + replacement with N ‐methyl‐D‐glucamine + (NMDG + ) or by omission of bath Ca 2+ . In contrast, ET depolarized the cells by 61 mV in the presence of low Cl − (6 mM), resulting in a complete breakdown of V m .3 In perforated patch clamp experiments, the ET‐induced whole‐cell current ( I ET ) exhibited a slight outward rectification with a reversal potential ( V rev ) of ‐22·7 mV. I ET was reduced by 85 % in low Cl − (6 mM), but was unaffected by Ca 2+ removal, Na + replacement with NMDG + , pipette K + replacement with Cs + or 1 mM Ni 2+ in the bath. 4 IET was unaffected by (+)‐isradipine (100 nM), a specific L‐type Ca 2+ channel (L‐VDCC) blocker. Transient inward Sr 2+ currents through L‐VDCCs were blocked by ET. 5 ET induced a biphasic Ca 2+ signal, consisting of a ‘peak’ and a ‘plateau’ elevation of [Ca 2+ ] i . Simultaneous patch clamp and fura‐2 measurements revealed that I ET coincided with intracellular Ca 2+ release but clearly outlasted the elevation of [Ca 2+ ] i . When the rise of [Ca 2+ ] i was prevented by pretreatment with thapsigargin in a Ca 2+ ‐free bath, both activation time and amplitude of I ET were reduced. Under these conditions, ET caused a decrease of [Ca 2+ ] i . 6 The Cl − channel blocker mefenamic acid (MFA) had a dual, concentration‐dependent effect on both I ET and the ET‐induced ‘plateau’ elevation of [Ca 2+ ] i : an increase at 10 μM, but an almost complete block at 100 μM. The effect of MFA on I ET preceded the effect on [Ca 2+ ] i . 7 The ET‐induced ‘plateau’[Ca 2+ ] i fell below control values in a low‐Cl − (6 mM) solution. 8 These data indicate an amplifying function of intracellular Ca 2+ release on an otherwise Ca 2+ ‐independent, unique Cl − current by ET. Moreover, this Cl − current appears to be functionally coupled with dihydropyridine (DHP)‐insensitive Ca 2+ entry, suggesting a modulatory role for long‐lasting effects of ET.