Fig. 9.

Relative ability of eight antagonists to block the three types of nicotinic response to 200 μm ACh expressed in approximate IC₅₀ values. Estimates of IC₅₀values were made by visual inspection of the data and have been established with the notion of obtaining a weighted rank ordering rather than of obtaining rigorously defined IC₅₀ values (see Results). A perusal of a given tone of column (black, gray, or white) permits an evaluation of the differential facility with which the different antagonists block a given response type. A comparison of the three column tones for each antagonist reveals the ability of a given antagonist to discriminate between the different response types. Empty columns with two asterisks are cases in which no effect (NE) on the ACh response was seen with the maximum concentration tested, the value of which is indicated in lieu of the data column. One asterisk indicates that the antagonist can induce a slight reduction in the tagged response, but that the highest concentration used failed to block the response by half (only case being that of 20 μm αCTx ImI on the sustained Cl response). V-d, Instances in which the block of the cationic response was voltage-dependent.