Abstract
Trains of action potentials cause Ca(2+)-dependent facilitation and inactivation of presynaptic P/Q-type Ca(2+) channels that can alter synaptic efficacy. A potential mechanism for these effects involves calmodulin, which associates in a Ca(2+)-dependent manner with the pore-forming alpha(1A) subunit. Here, we report that Ca(2+) and calmodulin dramatically enhance inactivation and facilitation of P/Q-type Ca(2+) channels containing the auxiliary beta(2a) subunit compared with their relatively small effects on channels with beta(1b). Tetanic stimulation causes an initial enhancement followed by a gradual decline in P/Q-type Ca(2+) currents over time. Recovery of Ca(2+) currents from facilitation and inactivation is relatively slow (30 sec to 1 min). These effects are strongly inhibited by high intracellular BAPTA, replacement of extracellular Ca(2+) with Ba(2+), and a calmodulin inhibitor peptide. The Ca(2+)/calmodulin-dependent facilitation and inactivation of P/Q-type Ca(2+) channels observed here are consistent with the behavior of presynaptic Ca(2+) channels in neurons, revealing how dual feedback regulation of P/Q-type channels by Ca(2+) and calmodulin could contribute to activity-dependent synaptic plasticity.