Table 1. Effects of saturating concentrations of nicotinic agonists on induction of transmitter release and whole-cell currents.
| DMPP (27) | Cytisine (22) | Nicotine (14) | ACh (10) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| EC50 (μM) | p | Emax | EC50 (μM) | p | Emax | EC50 (μM) | p | Emax | EC50 (μM) | p | Emax | |
| A. Current | 20.1 | 1.87 | 72.8 | 26.1** | 1.41** | 100.6* | 21.9 | 1.30** | 64.2 | 66.4** | 1.52** | 116.2** |
| ±0.7 | ±0.06 | ±5.2 | ±1.8 | ±0.03 | ±6.7 | ±1.7 | ±0.07 | ±8.3 | ±6.7 | ±0.07 | ±11.4 | |
| B. TTX-sensitive release | 3.86 | 4.03 | 2.59 | 7.01 | 1.58 | 3.47 | 7.60 | 3.18 | 3.13 | 7.45 | 4.11 | 0.95 |
| ±1.94 | ±1.57 | ±1.88 | ±1.66 | ±0.46 | ±0.30 | ±0.44 | ±0.42 | ±0.01 | ±1.94 | ±3.40 | ±0.06 | |
| C. TTX-insensitive release | 22.4 | 3.56 | 2.53 | 48.7 | 2.59 | 3.96 | 34.6 | 6.00 | 3.05 | 110.6 | 2.14 | 1.88 |
| ±4.6 | ±2.07 | ±0.20 | ±9.22 | ±0.78 | ±0.32 | ±1.2 | ±1.01 | ±0.13 | ±14.1 | ±0.27 | ±0.14 | |
| D. Ratio insensitive/sensitive | 5.80 | 0.97 | 6.94 | 1.14 | 4.55 | 0.97 | 14.84 | 1.97 | ||||
A, EC50 values, slope factors (p) and maximal effects (Emax, pA pF−1) for agonist-induced currents recorded by the perforated patch technique as described in Methods. Representative original current traces with concentration–response curves are shown in Fig. 4 Data points are the averaged parameters (± S.E.M.) from curve fits that were constructed for each individual cell (number of cells is given beside the agonist in parentheses). Statistical differences relative to the effects of DMPP were calculated by the Mann–Whitney test
P < 0.05
P < 0.01.
From this summary it appears that maximal effects of both nicotine and DMPP were smaller than those of ACh and cytisine. DMPP effects were also consistently smaller than either cytisine- or ACh-induced peak currents when compared in identical cells (cytisine, 106 ± 10 pA pF−1; DMPP, 74 ± 6 pA pF−1; means ± S.E.M.; P < 0.01, Wilcoxon test, n = 17; ACh, 116 ± 11 pA pF−1; DMPP, 69 ± 9 pA pF−1; P < 0.01, Wilcoxon test, n = 10; see also Fig. 4Aa and Ab). By contrast, a direct comparison of maximal effects of nicotine- and cytisine-induced currents in identical cells revealed no significant difference between the two substances (nicotine, 77 ± 5 pA pF−1; cytisine, 78 ± 5 pA pF−1; means ± S.E.M.; P > 0.05, Wilcoxon test, n = 5; see also Fig. 4Ba and Bb). Averaged cell capacitance was 33 ± 1 pF (mean ± S.E.M.), n = 41 cells. B, data points taken from curve fits of Fig. 2 and Fig. 3 (Emax, S%). TTX-sensitive release also stands for Cd2+ -sensitive release. C, data points taken from curve fits of Fig. 2 and Fig. 3. TTX-insensitive release also stands for Cd2+ -insensitive release. D, ratio of TTX-insensitive/TTX-sensitive transmitter release. Note that except for ACh, the ratio of EC50 values varies by a factor of about 6 (range, 4.55–6.94).