Large conductance calcium-activated potassium channels (also known as BK channels, KCa1, Slo, maxi-K) are unique among K+-channels in that they are activated both by intracellular calcium ions and by depolarization of the cell membrane. The BK-channels are widespread in the nervous system, but their functional roles in the mammalian brain are not yet fully understood. Recently, Storm´s group has shown that BK-channels in presynaptic terminals can regulate transmitter release in the brain, in several glutamatergic pathways within the hippocampus. It is also known that there are several types of voltage-gated calcium channels located in the glutamate terminals: N, P, Q, R, and possibly also L-type. However, it is still not known which of these calcium channel types that are functionally coupled to the presynaptic BK-channels, i.e. which of them provide the Ca2+-ions that can activate these BK-channels. The results from my research project provide several lines of evidence that N- and P/Q-type calcium channels activate the presynaptic BK-channels in stratum radiatum of rat hippocampus. However, my results are not sufficiently complete to reach a reliable conclusion. Hence, more experiments are needed to clarify this issue.