Figure 2.
(A) Intracellular calcium buffering prevents LTD. A Purkinje neuron was voltage-clamped with a patch pipette filled with solution containing 10 mM 1,2-bis(2-amino phenoxy)ethane-N,N,N′,N′-tetraacetic acid. Two pulses of InsP3+ΔV (arrows) failed to induce LTD. Experiment JL255A. (B) Evidence of saturation. A 30-s train of PF+ΔV (arrow) was used to induce LTD. Two subsequent 30-s trains of PF+ΔV (second and third arrows) failed to induce additional depression as maximal depression was achieved with the first train. Photo-release of InsP3+ΔV (hashed arrow) also failed to induce additional depression, which suggests a common pathway for both protocols. (C) The InsP3 receptor antagonist heparin (50 μg/ml in the patch pipette) prevented induction of LTD by 30-s (first arrow) and 100-s (second arrow) trains of PF+ΔV, indicating that InsP3-evoked calcium release is required for induction of LTD under physiological conditions. The transient decreases in responses after the trains are because of increases in membrane conductance presumably caused by calcium-activated K+ and Cl− channels. In all other figures amplitude of synaptic currents are shown after return of the membrane conductance to its resting level. Experiment JL166A.