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Ca 2+ and cAMP‐activated Cl − conductances mediate Cl − secretion in a mouse renal inner medullary collecting duct cell line
Author(s) -
Boese S. H.,
Glanville M.,
Aziz O.,
Gray M. A.,
Simmons N. L.
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.t01-1-00325.x
Subject(s) - ionomycin , forskolin , chemistry , symporter , medicine , biophysics , intracellular , ion transporter , endocrinology , bapta , membrane potential , extracellular , stimulation , microbiology and biotechnology , biology , biochemistry , membrane , transporter , gene
1 The nature of Cl − conductance(s) participating in transepithelial anion secretion by renal inner medullary collecting duct (IMCD, mIMCD‐K2 cell line) was investigated. 2 Extracellular ATP (100 μM) stimulated a transient increase in both whole‐cell Cl − conductance and intracellular free Ca 2+ . In contrast, ionomycin (10–100 nM) caused a sustained increase in whole‐cell Cl − conductance. Pre‐loading cells with the Ca 2+ buffer BAPTA abolished the ATP‐dependent responses and delayed the onset of the increase observed with ionomycin. 3 The Ca 2+ ‐activated whole‐cell Cl − current stimulated by ATP (peak) and ionomycin (maximal) displayed (i) a linear steady‐state current‐voltage relationship and (ii) time and voltage dependence with slow activation at +80 mV and slow inactivation at −80 mV. In BAPTA‐loaded cells, ionomycin‐elicited whole‐cell currents exhibited pronounced outward rectification with time‐dependent activation/inactivation. 4 Ca 2+ ‐activated and forskolin‐activated Cl − conductances co‐exist since ATP activation of whole‐cell current occurred during a maximal stimulation by forskolin in single cell recordings. 5 In IMCD epithelial layers, ATP and ionomycin stimulated an inward short circuit current ( I sc ) dependent upon basal medium Na + and Cl − /HCO 3 − but independent of the presence of apical bathing medium Na + and Cl − /HCO 3 − . This was identical to forskolin stimulation and consistent with transepithelial anion secretion. 6 PCR amplification of reverse‐transcribed mRNA using gene‐specific primers demonstrated expression of both cystic fibrosis transmembrane conductance regulator (CFTR) mRNA and Ca 2+ ‐activated Cl − channel (mCLCA1) mRNA in mIMCD‐K2 cells. 7 Ca 2+ and forskolin‐activated Cl − conductances participate in anion secretion by IMCD.