Effects on K+ currents in rat cerebellar granule neurones of a membrane-permeable analogue of the calcium chelator BAPTA.
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 microM BAPTA-AM inhibited both IKV and IKSO in cultured neurones, but did not seem to affect IKA. Neither 25 microM BAPTA (free acid) nor 25 microM 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 microM BAPTA-AM. 3. BAPTA-AM (2.5 microM) reduced IKV in short-term culture CG neurones, with further inhibition being seen when the perfusate was changed to one containing 25 microM 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 microM BAPTA-AM. 5. The degree of inhibition of IKV by 25 microM 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.
Watkins
C S
CS
Department of Pharmacology, Royal Free Hospital School of Medicine, London.
Mathie
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology*; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004594:Electrophysiology; D005260:Female; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D002614:Chelating Agents; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium