Alamethicin channel permeation by Ca2+, Mn2+ and Ni2+ in bovine chromaffin cells.
Alamethicin causes a concentration-dependent increase of [Ca2+]i in suspensions of bovine adrenal chromaffin cells loaded with fura-2. The basal levels of Cai2+ (234 +/- 37 nM; n = 4) increased to a maximum of 2347 +/- 791 nM (n = 3) with 100 micrograms/ml alamethicin. In the presence of 1 mM Cae2+ the increase reached a plateau within about 2-5 s. This increase was due to Ca2+ entry into chromaffin cells, since in the absence of Cae2+ alamethicin did not modify [Ca2+]i. This contrasts with ionomycin (1 microM) which produced a Cai2+ transient even in the absence of Cae2+. Mn2+ 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 Mn2+ which was drastically increased by cell depolarization by K+ (50 mM) addition. This suggests that Mn2+ is able to permeate voltage-dependent Ca2+ channels. Ni2+ uptake into either resting or K(+)-stimulated chromaffin cells was undetectable, but addition of alamethicin induced rapid uptake of this cation. The alamethicin-induced entry of Ni2+ was decreased by 50 mM K+. Overall, the results are compatible with the formation by alamethicin of ion channels in chromaffin cell plasma membranes.
Fonteríz
R I
RI
Departamento de Fisiología y Bioquímica, Facultad de Medicina, Universidad de Valladolid, Spain.
López
M G
MG
García-Sancho
J
J
García
A G
AG
D000408:Alamethicin / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D002417:Cattle; D002837:Chromaffin Granules / Q000378:metabolism*; D005454:Fluorescence Polarization; D007473:Ion Channels / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008345:Manganese / Q000378:metabolism*; D009532:Nickel / Q000378:metabolism*
D002413:Cations, Divalent; D007473:Ion Channels; D000408:Alamethicin; D008345:Manganese; D015759:Ionomycin; D009532:Nickel; D002118:Calcium