Abstract
Gramicidin is a thoroughly studied cation ionophore widely used to experimentally manipulate the plasma membrane potential (PMP). In addition, it has been established that the drug, due to its hydrophobic nature, is capable of affecting the organization of membrane lipids. We have previously shown that modifications in the plasma membrane potential of epithelial cells in culture determine reorganizations of the cytoskeleton. To elucidate the molecular mechanisms involved, we explored the effects of PMP depolarization on some putative signaling intermediates. In the course of these studies, we came across some results that could not be interpreted in terms of the properties of gramicidin as an ionic channel. The purpose of the present work is to communicate these results and, in general, to draw attention to the fact that gramicidin effects can be misleadingly attributed to its ionic or electrical properties. In addition, this work also contributes with some novel findings of the modifications provoked on the signaling intermediates by PMP depolarization and hyperpolarization.
Highlights
Ever since its discovery in the late thirties [1], gramicidin has been first employed as an antibiotic [2] and later as an experimental model for the study of the basic properties of ionic channels [3]
When BCE cells are incubated in physiological solutions containing gramicidin, they undergo plasma membrane potential (PMP) depolarization [5, 20]
In the absence of extracellular sodium, gramicidin provokes hyperpolarization [5]. These findings suggest that BCE cells possess a significantly larger permeability for potassium than for sodium, a typical property of most nonexcitable animal cells
Summary
Ever since its discovery in the late thirties [1], gramicidin has been first employed as an antibiotic [2] and later as an experimental model for the study of the basic properties of ionic channels [3]. As a consequence of its properties as an ionic channel, the ionophore has been widely employed as an additional experimental tool to provoke modifications in the plasma membrane potential in diverse cellular systems, mainly as a depolarizing agent [4,5,6,7,8,9,10]. If extracellular sodium is replaced by a nonpermeant cation (e.g., choline), gramicidin provokes hyperpolarization. It has been known for a long time that, besides its properties as an ionophore, gramicidin affects the membrane structural organization by direct interaction with constitutive lipids [14, 15]. The possibility of utilizing gramicidin and its derivatives as potential therapeutic agents for several diseases has reactivated the interest in this molecule [17,18,19]
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