N- and P/Q-type Ca2 channels mediate transmitter release with a similar cooperativity at rat hippocampal autapses

Abstract

The relationship between extracellular Ca2+ concentration and EPSC amplitude was investigated at excitatory autapses on cultured hippocampal neurons. This relationship was steeply nonlinear, implicating the cooperative involvement of several Ca2+ ions in the release of each vesicle of transmitter. The cooperativity was estimated to be 3.1 using a power function fit and 3.3 using a Hill equation fit. However, simulations suggest that these values underestimate the true cooperativity. The role of different Ca2+ channel subtype in shaping the Ca2+ dose-response relationship was studied using the selective Ca2+ channel blockers ω-agatoxin GIVA (ω- Aga), which blocks P/Q-type channels, and ω-cono..