Calcium specificity of the antigen-induced channels in rat basophilic leukemia cells.
Ion channels, activated upon IgE-Fc epsilon receptor aggregation by specific antigen, were studied in micropipet-supported lipid bilayers. These bilayers were reconstituted with purified IgE-Fc epsilon receptor complex and the intact 110-kDa channel-forming protein, both isolated from plasma membranes of rat basophilic leukemia cells (line RBL-2H3). In order to identify the current carrier through these ion channels and to determine their ion selectivity, we investigated the currents flowing through the IgE-Fc epsilon receptor gated channels in the presence of a gradient of Ca2+ ions. Thus, the solution in which the micropipet-supported bilayer was immersed contained 1.8 mM CaCl2, while the interior of the micropipet contained 0.1 microM Ca2+ (buffered with EGTA). Both solutions also contained 150 mM of a monovalent cation chloride salt (either K+ or Na+). The currents induced upon specific aggregation of the IgE (by either antigen or anti-IgE antibodies) were examined over a range of potentials imposed on the bilayer. The type of conductance event most frequently observed under the employed experimental conditions was a channel that has a slope conductance of 3 pS and a reversal potential practically identical with the calculated value for the reversal potential of calcium (134 +/- 11 mV in the presence of sodium, 125 +/- 13 mV in the presence of potassium). These results indicate that this channel is highly selective for calcium against the monovalent cations sodium and potassium. This same channel has a conductance of 4-5 pS in the presence of symmetrical solutions containing only 100 mM CaCl2 and 8 pS in the presence of 0.5 M NaCl with no calcium.(ABSTRACT TRUNCATED AT 250 WORDS)
Corcia
A
A
Department of Membrane Research, Weizmann Institute of Science, Rehovot, Israel.
Pecht
I
I
Hemmerich
S
S
Ran
S
S
Rivnay
B
B
D000818:Animals; D000941:Antigens / Q000276:immunology; D015220:Calcium Channels / Q000276:immunology / Q000378:metabolism*; D002122:Calcium Chloride / Q000494:pharmacology; D002462:Cell Membrane / Q000032:analysis; D004553:Electric Conductivity; D004591:Electrophoresis, Polyacrylamide Gel; D004594:Electrophysiology; D007073:Immunoglobulin E / Q000378:metabolism; D007946:Leukemia, Mast-Cell; D008051:Lipid Bilayers / Q000378:metabolism; D008407:Mast Cells / Q000032:analysis* / Q000276:immunology; D008565:Membrane Proteins / Q000276:immunology / Q000302:isolation & purification / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011961:Receptors, Fc / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000941:Antigens; D015220:Calcium Channels; D008051:Lipid Bilayers; D008565:Membrane Proteins; D011961:Receptors, Fc; D007073:Immunoglobulin E; D012965:Sodium Chloride; D011189:Potassium Chloride; D002122:Calcium Chloride