Regulation of an outwardly rectifying chloride conductance in renal epithelial cells by external and internal calcium.
We have used perforated patch clamp and Fura-2 microfluorescence measurements to study Ca(2+)-activated Cl- currents in cultured mouse renal inner medullary collecting duct cells (mIMCD-3). The conductance was spontaneously active under resting conditions and whole cell currents were time and voltage-independent with an outwardly rectifying current-voltage relationship. The channel blockers DIDS, niflumic acid, glybenclamide and NPPB reversibly decreased the basal currents, whereas the sulfhydryl agent, DTT produced an irreversible inhibition. Increasing or decreasing extracellular calcium produced parallel changes in the size of the basal currents. Variations in external Ca2+ were associated with corresponding changes in free cytosolic Ca2+ concentration. Increasing cytosolic Ca2+ by extracellular ATP or ionomycin, further enhanced Cl- conductance, with whole cell currents displaying identical biophysical properties to the basal currents. However, the agonist-stimulated currents were now increased by DTT exposure, but still inhibited by the other channel blockers. Using RT-PCR, three distinct mRNA transcripts belonging to the CLCA family of Ca(2+)-activated Cl- channel proteins were identified, two of which represent novel sequences. Whether different channels underlie the basal and agonist-stimulated currents in mIMCD-3 cells is unclear. Our findings establish a novel link between alterations in external and internal Ca2+ and the activity of Ca(2+)-activated Cl- transport in these cells.
Department of Physiological Sciences, University Medical School, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK.
G S
GS
Stewart
M
M
Glanville
O
O
Aziz
N L
NL
Simmons
M A
MA
Gray
D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D004847:Epithelial Cells; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
C492109:CLCA1 protein, human; D018118:Chloride Channels; D002712:Chlorides; C492299:Clca2 protein, mouse; C116464:Clca3a1 protein, mouse; D000255:Adenosine Triphosphate; D002118:Calcium