The K+ channel iKCA1 potentiates Ca2+ influx and degranulation in human lung mast cells.
BACKGROUND
Human lung and blood-derived mast cells express a Ca2+-activated K+ channel (KCA) that has electrophysiological properties resembling the intermediate conductance KCA (iKCA1). This channel is predicted to enhance IgE-dependent mast cell responses.


OBJECTIVE
To confirm the identity of this channel as iKCA1 in human lung mast cells and to examine the effect of an iKCA1 opener, 1-ethyl-2-benzimidazolinone (1-EBIO), on Ca2+ influx and degranulation after IgE-dependent activation.


METHODS
iKCA1 expression was examined by using RT-PCR. Ion currents were measured by using the patch clamp technique in human peripheral blood-derived mast cells, freshly isolated human lung mast cells (HLMCs), and long-term cultured HLMCs (LTHLMCs). Currents were manipulated with the specific iKCA1 opener 1-EBIO and the iKCA1 blockers clotrimazole and TRAM-34. Ratiometric Ca2+ imaging was performed on single fura-2-loaded cells, and histamine release was measured by radioenzymatic assay.


RESULTS
Both fresh HLMCs and LTHLMCs expressed iKCA1 mRNA. The iKCA1 opener 1-EBIO induced iKCA1 currents in 89% of human peripheral blood-derived mast cells, 12% of fresh HLMCs, and 67% of LTHLMCs, which were blocked by the iKCA1 blockers clotrimazole and TRAM-34. After cell activation with a suboptimal concentration of anti-IgE, 1-EBIO enhanced the IgE-dependent rise in cytosolic-free Ca2+ and potentiated IgE-dependent histamine release.


CONCLUSIONS
Opening of iKCA1 enhances IgE-dependent Ca2+ influx and histamine release in HLMCs. Inhibition of iKCA1 may provide a novel approach to the treatment of mast cell-mediated disease.
Mark Duffy
S
S
Department of Infection, Immunity and Inflammation, Institute for Lung Health, University of Leicester Medical School, UK.
Berger
Patrick
P
Cruse
Glenn
G
Yang
Weidong
W
Bolton
Sarah J
SJ
Bradding
Peter
P
D001562:Benzimidazoles / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015550:Cell Degranulation / Q000187:drug effects / Q000276:immunology*; D002478:Cells, Cultured; D003022:Clotrimazole / Q000494:pharmacology; D006632:Histamine / Q000276:immunology; D006801:Humans; D007073:Immunoglobulin E / Q000276:immunology; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D008168:Lung / Q000166:cytology / Q000276:immunology; D008407:Mast Cells / Q000187:drug effects / Q000276:immunology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology
D001562:Benzimidazoles; D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D015221:Potassium Channels; D011720:Pyrazoles; C411671:TRAM 34; D007073:Immunoglobulin E; D006632:Histamine; D003022:Clotrimazole; C102635:1-ethyl-2-benzimidazolinone; D002118:Calcium