Blockade of Ca 2+ -activated K + channels by galantamine can also contribute to the potentiation of catecholamine secretion from chromaffin cells Eva Alés a , Francesca Gullo c , Esperanza Arias a , Román Olivares a , Antonio G. García a,b , Enzo Wanke c , Manuela G. López a,b, ⁎ a Instituto Teófilo Hernando. Departamento de Farmacología y Terapéutica, Facultad de Medicina, U.A.M., Universidad Autónoma de Madrid, C/, Arzobispo Morcillo 4, E-28029 Madrid – Spain b Instituto Universitario de Investigación Gerontológica y Metabólica and Servicio de Farmacología Clínica, Hospital de la Princesa, Madrid, Spain c Dipartimento di Biotecnologie e Bioscienze, Università of Milano-Bicocca, Piazza della Scienza 2, I-20126 Milano – Italy Received 16 November 2005; received in revised form 14 July 2006; accepted 19 July 2006 Available online 28 July 2006 Abstract Galantamine is a drug in clinical use for the treatment of Alzheimer's disease, but its mechanism(s) of action remains controversial. Here we addressed the question whether galantamine could potentiate neurotransmitter release by inhibiting small conductance Ca 2+ -activated K + channels (K Ca 2). Galantamine potentiated catecholamine secretory responses induced by 10 s pulses of acetylcholine and high [K + ] o applied to fast- superfused bovine adrenal chromaffin cell populations. Catecholamine release was significantly enhanced by galantamine although we did not find concentration dependence in the range 0.1–1 μM. The K Ca 2 channel blocker apamin (0.3 μM) occluded the potentiating effects of galantamine on acetylcholine-evoked secretion. Like apamin, galantamine also modified the firing of action potentials, but to a lesser extent. In addition, 1 μM galantamine reduced by 41% the K Ca 2 current without modifying the voltage-dependent Ca 2+ currents. These results constitute the first direct evidence that galantamine can potentiate neurotransmitter release by blocking K Ca 2 channels, in addition to its already demonstrated capacity to mildly block acetylcholinesterase or potentiate allosterically nicotinic receptors. © 2006 Elsevier B.V. All rights reserved. Keywords: Galantamine; K Ca 2 channels; Catecholamines; Chromaffin cell; Apamin 1. Introduction Alzheimer's disease is a progressive, degenerative disease with a constellation of symptoms that clearly suggest a complex etiology involving abnormal function and morphology in sev- eral neurotransmitter systems. For years, a strategy to improve cognitive function in Alzheimer patients has been the enhance- ment of cholinergic neurotransmission in the brain by inhibition of acetylcholinesterase. However, the therapeutic success of these compounds has been limited. Galantamine (an alkaloid extracted originally from the daffodil bulb galanthus nivalis) is an acetylcholinesterase inhibitor used in the clinic that, in ad- dition to blocking acetylcholinesterase with a mild potency (Thomsen et al., 1991; Woodruff-Pak et al., 2002) behaves as an allosteric potentiating ligand at nicotinic receptors (Schratten- holz et al., 1996; Albuquerque et al., 1997; Samochocki et al., 2003). Galantamine has been shown to potentiate glutamatergic and GABA-ergic (Gamma-aminobutyric acid ) neurotransmis- sion between Schaffer collaterals and CA1 neurons (Santos et al., 2002) and also to potentiate nicotine-evoked increases in intracelullar Ca 2+ and [ 3 H]noradrenaline release in SH-SY5Y cells (Dajas-Bailador et al., 2003). The current hypothesis by which galantamine enhances synaptic transmission is by acting on nicotinic receptors as an allosteric potentiating ligand. However, we had very preliminary results from our labo- ratory showing that galantamine could also enhance K + induced catecholamine secretion; this suggested to us that another mechanism could be involved in galantamine's mechanism of action, besides allosteric modulation of nicotinic receptors. European Journal of Pharmacology 548 (2006) 45 – 52 www.elsevier.com/locate/ejphar ⁎ Corresponding author. Departamento de Farmacología, Facultad de Medicina. U.A.M. C/ Arzobispo Morcillo 4, 28029 Madrid – Spain. Tel.: +34 91 4975386; fax: +34 91 4975397. E-mail address: manuela.garcia@uam.es (M.G. López). 0014-2999/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ejphar.2006.07.032