Further kinetic analysis of the chemically modified acetylcholine receptor.

The acethylcholine receptor was chemically modified using bisulfite to add a sulfonate group to a disulfide bond on the alpha subunit, and diamide, an oxidizing agent, to form an interchain disulfide bond between beta subunits of adjacent receptors. In previous work, both reagents increased mepc decay times but produced no change in mean channel open time or conductance as measured by spectral analysis of endplate current fluctuations (Steinacker and Zuazaga 1981). In the current work, we show that, while both chemical modifications increase the decay time of the miniature endplate current, only sulfonation increases the time to peak. Sulfonation also produced an effect on voltage jump current relaxation time, which parallels the increase in miniature endplate current decay time, and an increase in the ratio of the current relaxation amplitudes. Diamide had no effect on voltage jump current relaxation amplitudes or time constants. These data are analyzed in an attempt to correlate changes in specific rate constants to changes in the macroscopic current measurements.