help button home button Biophys. J.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS

Biophysical Journal 24: 135-160 (1978)
© 1978 the Biophysical Society

This Article
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Related articles in Biophys. J.
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Nass, M M
Right arrow Articles by Krouse, M E
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Nass, M M
Right arrow Articles by Krouse, M E

Response of acetylcholine receptors to photoisomerizations of bound agonist molecules.

M M Nass, H A Lester and M E Krouse

ABSTRACT

In these experiments, agonist-induced conductance is measured while a sudden perturbation is produced at the agonist-receptor binding site. A voltage-clamped Electrophorus electroplaque is exposed to trans-Bis-Q, a potent agonist. Some channels are open; these receptors have bound agonist molecules. A light flash isomerizes 3(-35)% of the trans-Bis-Q molecules to their cis form, a far poorer agonist. This causes a rapid decrease of membrane conductance (phase 1), followed by a slower increase (phase 2). Phase 1 has the amplitude and wavelength dependence expected if the channel closes within 100 mus after a single bound trans-Bis-Q is isomerized, and if the photochemistry of bound Bis-Q resembles that in solution. Therefore, the receptor channel responds rapidly, and with a hundred-fold greater closing rate, after this change in the structure of a bound ligand. Phase 2 (the conductance increase) seems to represent the relaxation back toward equilibrium after phase 1, because (a) phase 2 has the same time constant (1(-5) ms) as a voltage- or concentration-jump relaxation under identical conditions; and (b) phase 2 is smaller if the flash has led to a net decrease in (trans-Bis-Q). Still slower signals follow: phase 3, a decrease of conductance (time constant 5(-10 ms); and phase 4, an equal and opposite increase (several seconds). Phase 3 is abolished by curare and does not depend on the history of the membrane voltage. We consider several mechanisms for phases 3 and 4.


Related articles in Biophys. J.:

DISCUSSION

Biophys. J. 1978 24: 154-160. [PDF]  





HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 1978 by the Biophysical Society.