Fig. 1.

Sensitivity of epinephrine activated secretion to K_Ca1.1 blockers. Isolated mucosae were stimulated by epinephrine addition to the serosal solution from the standard basal condition with electrogenic secretion monitored by short-circuit current (I_sc) (see methods). A: I_sc was measured in adjacent mucosae during basal conditions with addition of IbTx (300 nM) to the mucosal solution of one (dotted line). B: adjacent mucosae were stimulated by epinephrine (5 μM) with one pretreated by mucosally added IbTx (200 nM) 60 min prior to epinephrine (dotted line). C: a third mucosa adjacent to those shown in panel B was treated with three successive concentrations of IbTx (10, 100, and 200 nM) beginning after epinephrine stimulation (dotted line), control (solid line), and IbTx pretreatment (dashed line). D and E: responses of epinephrine-activated I_sc (^epiI_sc) and transepithelial conductance (^epiΔG_t) to 3 concentrations of IbTx were measured with an adjacent mucosa as time control. Control ^epiI_sc and ^epiΔG_t were −125.8 ± 15.2 μA/cm² and +6.13 ± 1.34 mS/cm² (○, n = 3), respectively. Fractional inhibition by IbTx was corrected for any time-dependent changes, averaged, and scaled to the control ^epiI_sc or ^epiΔG_t (●). Values significantly different from control (P < 0.05) are indicated by an asterisk (*). A fit of Henri-Michaelis-Menten kinetics with a single binding site was made to the concentration dependence from each mucosa and the average (n = 3) shown as a dashed line: ^epiI_sc, ^IbTxIC₅₀ = 193 ± 41 nM, maximal fractional inhibition = 0.513 ± 0.121; ^epiΔG_t, ^IbTxIC₅₀ = 220 ± 77 nM, maximal fractional inhibition = 0.476 ± 0.040. An additional fit was made assuming that IbTx could inhibit ^epiI_sc or ^epiΔG_t completely (dotted line). F: adjacent mucosae were stimulated by epinephrine (1.0 μM) with one pretreated by paxilline (1.0 μM) addition to both mucosal and serosal solutions 35 min prior to epinephrine (dotted line).