1. Whole cell recordings of voltage-activated K+ currents were made with the amphotericin B perforated patch technique from cerebellar granule (CG) neurones of 6–8 days rats that had been in culture for 1 to 16 days. By use of appropriate voltage protocols, the effects of the membrane-permeant form of BAPTA, 1,2-bis-(2-amino-phenoxy)ethane-N,N,N′,N′-tetraacetic acid acetoxymethyl ester (BAPTA-AM), on the transient A current (IKA), the delayed rectifier current (IKv) and a standing outward current (IKso) were investigated. 2. Bath application of 25 μm BAPTA-AM inhibited both IKv and IKso in cultured neurones, but did not seem to affect IKA. Neither 25 μm BAPTA (free acid) nor 25 μm ethylenediaminetetraacetic acid acetoxymethyl ester (EDTA-AM) had any significant effect on the magnitude of IKso. Similarly in short-term (1–2 days) cultured CG neurones IKv, but not IKA, was inhibited by 25 μm BAPTA-AM. 3. BAPTA-AM (2.5 μm) reduced IKv in short-term culture CG neurones, with further inhibition being seen when the perfusate was changed to one containing 25 μm BAPTA-AM. 4. Tetraethylammonium ions (TEA) (10 mM) reversibly inhibited IKv in these cells with a similar rate of block of IKv to that induced by 25 μm BAPTA-AM. 5. The degree of inhibition of IKv by 25 μm BAPTA-AM was both time- and voltage-dependent, in contrast to the inhibition of this current by TEA. 6. These data indicate that BAPTA-AM reduces K+ currents in cerebellar granule neurones and that this inhibition cannot be explained in terms of intracellular Ca2+ chelation, but is a direct effect on the underlying channels. |