Abstract
Presynaptic calcium influx at most excitatory central synapses is carried by both Cav2.1 and Cav2.2 channels. The kinetics and modulation of Cav2.1 and Cav2.2 channels differ and may affect presynaptic calcium influx. We compared release dynamics at CA3/CA1 synapses in rat hippocampus after selective blockade of either channel subtype and subsequent quantal content restoration. Selective blockade of Cav2.1 channels enhanced paired-pulse facilitation, whereas blockade of Cav2.2 channels decreased it. This effect was observed at short (50 msec) but not longer (500 msec) intervals and was maintained during prolonged bursts of presynaptic activity. It did not reflect differences in the distance of the channels from the calcium sensor. The suppression of this effect by preincubation with the G(o/i)-protein inhibitor pertussis toxin suggests instead that high-frequency stimulation relieves inhibition of Cav2.2 by G(o/i), thereby increasing the number of available channels.