Characterization and modulation of [125I]iberiotoxin-D19Y/Y36F binding in the guinea-pig urinary bladder.
The radioligand binding characteristics of the Ca(2+)-activated K(+) channel ligand [125I]iberiotoxin-D19Y/Y36F were examined in guinea-pig urinary bladder membranes. Saturation analysis revealed a single class of high affinity binding sites in the bladder with a K(D) value of 45.6 pM and a B(max) value of 112 fmol/mg protein. Specific binding was displaced by unlabeled iberiotoxin and penitrem A, but not by blockers of other classes of K(+) channels including alpha-dendrotoxin, margatoxin and apamin. The indole alkaloids, paxilline and verruculogen, significantly increased binding by 4.5- and 4.3-fold, respectively. Tetraacetic acid derivatives such as ethylenediamine tetraacetic acid and ethyleneglycoltetraacetic acid enhanced specific [125I]iberiotoxin-D19Y/Y36F binding about 2.5-fold, which was not attributable to calcium chelation. This increase was due to a significant change in ligand binding affinity (K(D)=6.3 pM), but not due to a change in the B(max), indicating that these compounds may enhance toxin binding via allosteric interactions. Collectively, these results demonstrate that the binding sites for [125I]iberiotoxin-D19Y/Y36F present in the urinary bladder shows a pharmacological profile typical of maxi-K(+) channels and can be modulated, not only by previously known indole alkaloids, but also by tetraacetic acid analogs.
Molinari
E J
EJ
Neurological and Urological Diseases Research, D-47C, 3rd Floor, Bldg. AP9A, Pharmaceutical Products Division, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064-3500, USA.
Sullivan
J P
JP
Wan
Y
Y
Brioni
J D
JD
Gopalakrishnan
M
M
D000818:Animals; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008024:Ligands; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D010455:Peptides / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated; D011869:Radioligand Assay; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*
D051036:Large-Conductance Calcium-Activated Potassium Channels; D008024:Ligands; D010455:Peptides; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; C120554:iberiotoxin-D19Y-Y36F