The decay of stimulus-evoked, AMPA receptor–mediated EPSCs became faster when glutamate release was reduced. A, Currents recorded in control extracellular solution (2 mm Ca²⁺ and 1 mmMg²⁺) and in low-calcium solution (0.5 mm Ca²⁺ and 2.5 mmMg²⁺). B, The same currents, scaled to the same peak amplitude. The current decay was faster in low-calcium solution. C, Currents evoked by paired stimuli at a 2 sec interval. D, Currents evoked by the first and second stimuli, scaled to the same peak amplitude. The second, depressed EPSC decayed faster than did the first response. Cells were held at −75 mV.