Comparison of the initial gradients for the concentration dependence of the effect of amilorides on the dissociation of [3H]prazosin or [3H]yohimbine from the α1A- or α2A-adrenergic receptors, respectively
| Amiloride | n | α1A-Adrenergic Receptor | α2A-Adrenergic Receptor | ||
|---|---|---|---|---|---|
| Initial Gradient K2 ∗ (k−2 −k−1) | Affinity ∗ Fold Increase K2 ∗ (k−2 −k−1)/k−1 | Initial GradientK2 ∗ (k−2 −k−1) | Affinity ∗ Fold Increase K2 ∗ (k−2 −k−1)/k−1 | ||
| Amiloride | 4 | 43 ± 3 | 2,100 | 3.4 | 101 |
| DMA | 6 | 102 ± 5 | 4,900 | 34 | 1,010 |
| BZA | 2 | 141 ± 3 | 6,700 | 11 | 310 |
| EPA | 2 | 186 ± 3 | 8,800 | 270 | 7,900 |
| MBA | 2 | 187 ± 2 | 8,900 | 400 | 12,000 |
| HMA | 3 | 393 ± 20 | 19,000 | 1,100 | 32,000 |
For the α1A-adrenergic receptor, the initial gradient estimates were derived as described in the legend of Fig. 5, and are expressed as means ± S.E. of n experiments. For the α2A-adrenergic receptor, the values were calculated with published data (Leppik et al., 1998). To enable comparison, each estimate was divided by the antagonist dissociation rate (k −1) in the absence of amiloride analog (0.0212 ± 0.0004 min−1 for [3H]prazosin/α1A-adrenergic receptor, 0.034 ± 0.001 min−1 for [3H]yohimbine/α2A-adrenergic receptor). Thek −2 is the antagonist dissociation rate from the amiloride analog-occupied receptor, and K 2 is the affinity of the amiloride analog at the antagonist-occupied receptor.