Figure 4.

Coadministration of DELT and CLON inhibits K⁺-evoked release of CGRP from spinal cord slices in a synergistic manner. A, K⁺-evoked release of CGRP was challenged by administration of DELT, CLON and their combination. DELT (filled squares) and CLON (filled circles) inhibited the release of CGRP in a concentration-dependent manner with similar potency and efficacy. Coadministration of DELT and CLON at constant concentration ratio of 1:1 (open squares and open triangles) was ∼30-fold more potent than either drug given alone, suggesting that the interaction was synergistic. Error bars represent mean ± SEM for each concentration point (n = 3–9 samples/concentration). B, Isobolographic analysis of the data in Figure 3A. The y-intercept represents the CLON EC₅₀ (1.9 nm; 95% CI = 0.5–3.3), and the x-intercept represents the DELT EC₅₀ (2.3 nm; 95% CI = 0.5–4.2) when each was administered alone. The heavy line connecting the intercepts is the theoretical additive line and the open circle represents the theoretical additive combined EC₅₀. Coordinates for drug combinations falling below this line and outside the confidence limits indicate a synergistic interaction. Coadministration of CLON and DELT at a 1:1 concentration ratio resulted in an EC₅₀ (0.06; 95% CI = 0.01–0.1) of DELT in the presence of CLON that fell well below the additive line, indicating that the interaction was synergistic. Error bars parallel to each axis represent the lower 95% CI for each compound given alone. The error bars on the combined concentration points represent the upper and lower 95% CIs.