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Alamethicin channel permeation by Ca 2+ , Mn 2+ and Ni 2+ in bovine chromaffin cells
Author(s) -
Fonteriz R.I.,
López M.G.,
Garcia-Sancho J.,
Garcia A.G.
Publication year - 1991
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(91)80560-p
Subject(s) - alamethicin , chromaffin cell , ionomycin , chemistry , biophysics , analytical chemistry (journal) , membrane potential , depolarization , membrane , adrenal medulla , intracellular , chromatography , biochemistry , endocrinology , biology , catecholamine , lipid bilayer
Alamethicin causes a concentration‐dependent increase of (Ca 2+ ), in suspensions of bovine adrenal chromaffin cells loaded with fura‐2. The basal levels of Ca 2+ (234 ± 37 nM; n =4) increased to a maximum of 2347±791 nM ( n =3) with 100 μg/ml alamethicin. In the presence of 1 nM Ca 2+ the increase reached a plateau within about 2–5 s. This increase was due to Ca 2+ entry into chromaffin cells, since in the absence of Ca 2+ alamethicin did not modify [Ca 2+ ]. This contrasts with ionomycin (1 μM) which produced a Ca 2+ transient even in the absence of Ca 2+ , Mn 2+ ions also entered chromaffin cells in the presence of alamethicin, as measured by the quenching of fura‐2‐fluorescence following excitation at 360 nm. Resting chromaffin cells had a measurable permeability to Mn 2+ which was drastically increased by cell depolarization by K + (50 nM) addition. This suggests that Mn 2+ is able to permeate voltage‐dependent Ca 2+ channels. Ni 2+ uptake into either resting of K + ‐stimulated chromaffin cells was undetectable, but addition of alamethicin induced rapid uptake of this cation. The alamethicin‐induced entry of Ni 2+ was decreased by 50 mM K + . Overall, the results are compatible with the formation by alamethicin of ion channels in chromaffin cell plasma membranes.