Dose-dependent effects of the NSP4114-135 and NV464-483 peptides on the initial rate of pH gradient-activated chloride uptake by rabbit intestinal BBM vesicles. Fixed amounts of BBM vesicles were mixed with variable amounts of peptide in the appropriate volume of membrane (Tris gluconate) buffer to give the indicated (final) peptide concentrations. After preincubation for 5 min at 22°C, aliquots were used to measure the initial rate of 15 mM chloride uptake in the presence of an initial pHo/pHi = 5.0/7.5 gradient. Symbols: (▲) for NSP4114-135 and (△) for NV464-483. Results are shown as absolute uptake rates in pmoles·mg membrane protein-1·s-1 ± standard deviation with 6 – 15 determinations per point. Because the two peptides gave statistically indistinguishable results, the two sets of data were pooled to obtain the overall fits in Table 1. The continuous line illustrates the best overall fit obtained by fixing the ni value to 1.