From owner-biophysics@net.bio.net Sun Feb 08 22:00:00 1998 Path: biosci!daresbury!not-for-mail From: Pentcho Valev Newsgroups: bionet.biophysics Subject: Membrane capacitance Date: 9 Feb 1998 08:08:17 -0000 Lines: 33 Sender: lpddist@mserv1.dl.ac.uk Distribution: bionet Message-ID: <6bmdhh$gsq@mserv1.dl.ac.uk> Original-To: biophys@dl.ac.uk Jonathan Marder wrote:>>>>>>>>>>>>>>>>>> Pentcho, this is really not so mysterious. There are lateral movements of ions until electroCHEMICAL equilibrium is reached. Once this happens, there will be no more net ion fluxes. I see no problem with membrane patches attracting concentrations of particular ions - in fact I expect that this is documented in the literature.<<<<<<<<<<<<<<<<<<< It seems to me that there will be lateral fluxes even at equilibrium (although half of my mind rejects this as absurd). Let us have a close look at the situation: pH 2 -------high-capacitance---------low-capacitance----------------------- pH 7 The membrane is permeable only to H+. If (at equilibrium) the potential in each compartment is uniform (this is universally accepted), there will be a lateral gradient of H+ concentration close to the membrane - e.g., in the lower compartment, the H+ concentration will be higher at the high-capacitance patch than at the low-capacitance one. As the potential is uniform, we should expect a lateral H+ flux from the high-capacitance patch to the low-capacitance one (in the lower compartment). The other possible assumption is that, at equilibrium, the potential in each compartment is not uniform. We could analyse this situation as well but it is clear even without analysis that, if correct, the assumption would disturb the established theoretical paradigm to such an extent that practically a new theory will have to be built. Best regards, Pentcho .