Photoactivation and dissociation of agonist molecules at the nicotinic acetylcholine receptor in voltage-clamped rat myoballs.
The photochemical properties of the azobenzene derivative, Bis-Q, were exploited to carry out an agonist concentration jump followed by a molecular rearrangement of bound agonist molecules at acetylcholine (ACh) receptor channels of voltage-clamped rat myoballs. Myoballs were bathed in solutions containing low concentrations of cis-Bis-Q, the inactive isomer. Whole-cell current relaxations were studied following a light flash that produced a concentration jump of agonist, trans-Bis-Q, followed by a second flash that produced net trans----cis photoisomerizations of Bis-Q molecules. The concentration-jump relaxation provided a measure of the mean burst duration for ACh receptor channels occupied by trans-Bis-Q (7.7 ms, 22 degrees C). The second current relaxation was a more rapid conductance decrease (phase 1, tau = 0.8 ms). Phase 1 may represent either the burst duration for receptors initially occupied by a single cis- and a single trans-Bis-Q molecule or that for unliganded receptors. Single-channel current recordings from excised outside-out membrane patches showed that single channels open following an agonist concentration jump comparable to that used in the whole-cell experiments; when many such records were averaged, a synthetic macroscopic relaxation was produced. Individual open channels closed faster following a flash that promoted trans----cis photoisomerizations of the bound ligand, thus confirming the whole-cell observations of phase 1.
L D
LD
Chabala
A M
AM
Gurney
H A
HA
Lester
D000818:Animals; D002478:Cells, Cultured; D004553:Electric Conductivity; D007473:Ion Channels / Q000502:physiology; D008027:Light; D009132:Muscles / Q000502:physiology*; D010777:Photochemistry; D000644:Quaternary Ammonium Compounds; D051381:Rats; D011978:Receptors, Nicotinic / Q000502:physiology*
D007473:Ion Channels; D000644:Quaternary Ammonium Compounds; D011978:Receptors, Nicotinic; C000295:Bis-Q