ELSEVIER European Journal of Pharmacology 280 (1995) 215-219 eJD Short communication NS 1619 activates BKca channel activity in rat cortical neurones Kevin Lee, Iain C.M. Rowe, Michael L.J. Ashford * Department of Pharmacology, Universityof Cambridge, Tennis Court Road, Cambridge, CB2 1Q J, UK Received 14 March 1995; accepted 25 April 1995 Abstract Single channel recordings of large conductance Ca2+-activated K + (BKca) channels were made from neurones isolated from rat motor cortex. Application of levcromakalim, pinacidil or diazoxide had no effect on BKca channel activity in excised patches. In contrast, NS 1619 (•-(2'-hydr•xy-5'-triflu•r•methy•pheny•)-5-triflu•r•methy•-2(3H)benzimidaza••ne) induced concentration- dependent activation of BKca channels with a calculated ECs0 of 32/zM. The NS 1619-induced activity was dependent on the presence of free Ca 2+ at the intracellular surface, but was not associated with a change in channel voltage sensitivity. Niflumic acid had no effect on BKca activity per se but prevented NS 1619-mediated activation. Keywords: NS 1619; BKca channel; Niflumic acid; Motor cortex 1. Introduction The potassium channel openers are a heterogeneous group of chemical compounds generally assumed to act upon ATP-sensitive K + (KA-rP) channels, a view par- tially supported by single channel recordings and the ability of sulphonylureas to block the potassium cur- rents induced by these agents (Edwards and Weston, 1993). However, it has been reported that pinacidil, one of the established or 'classical' potassium channel openers, can also increase large conductance Ca 2+- activated K ÷ (BKca) channel activity in smooth muscle (Gelband et al., 1989; Ashford et al., 1993). The list of potassium channel openers has recently expanded to include the benzimidazalone derivative NS 1619 (1-(2'- hydroxy-5'-trifluoromethylphenyl)-5-trifluoromethyl- 2(3H)benzimidazalone), which activates BKc~ chan- nels in a number of tissues (Olesen et al., 1994; Sellers and Ashford, 1994; Edwards et al., 1994), and the structurally related compound niflumic acid, which stimulates BKca channels in coronary smooth muscle (Toro et al., 1993). In the present study the action of three 'classical' potassium channel openers (diazoxide, pinacidil and levcromakalim) and two of the newer agents (NS 1619 * Corresponding author. Tel. (0223) 334017, fax (0223) 334040. 0014-2999/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0014-2999(95)00251-0 and niflumic acid) were examined on BKca channels in rat cortical neurones. These BKca channels are also activated by application of ATP to the cytoplasmic aspect of excised patches, an effect likely mediated by phosphorylation (Lee et al., 1994a). 2. Materials and methods 2.1. Preparation o f acutely dispersed cortical neurones Coronal slices (350 /xm thick) of cerebral cortex were cut from brains of male Sprague-Dawley rats (100-200 g weight) with a vibratome (Oxford Instru- ments). Portions of the motor cortex were dissected from the coronal sections and were incubated in 1 mg per ml Pronase E (Sigma) in artificial cerebral-spinal fluid gassed with 95% 0 2 and 5% CO 2 at 37°C for 10 min and then titurated by use of flame-polished Pas- teur pipettes of decreasing internal diameter. The dis- persed cells were plated onto tissue culture dishes and left for 30 min-1 h before use by which time the cells had adhered to the plates. 2.2. Recording and analysis All experiments were performed using either the inside-out or the outside-out configuration of the patch