Effects of 2-MeSATP and ATP on catecholamine release. A. Amperometric currents recorded from chromaffin cell batches in response to brief pulses of increasing 2-MeSATP and ATP concentrations. Cells were allowed to rest for ~10 min between successive applications. Nominal agonist concentrations (in μM) are indicated beneath each trace. Nominal concentrations of test agents are used throughout this legend. Actual concentrations at the cell bed differ from nominal concentrations by a factor of 1.64 (see Methods). Concentrations along the X axis in Fig. 3B are actual concentrations at the cell bed; B. Dose-response curves of catecholamine release evoked by 2-MeSATP and ATP (circles and squares, respectively). Data from the experiment depicted in A and two similar experiments. Also depicted are data for UTP (100 μM; filled square) as well as for 2-MeSATP stimulations in presence of 50 μM PPADS (diamond), in the virtual absence of extracellular Ca2+ (EGTA-containing solution, inverted triangle) and in absence of extracellular Na+ (Na+ replacement for NMG+, triangle) (n = 3 experiments for each condition).