Colloids and Surfaces A: Physicochemical and Engineering Aspects. ll(l993) 119- 124 Elsevier Science Publishers B.V., Amsterdam 119 Modulation of surface flow by divalent cations and protons C.A. PasternakaT*, C.L. Bashford”, Y.E. Korchevbv’, T.K. Rostovtsevabv’ and A.A. Levb ‘Department of Cellular and M olecular Sciences, St. George’s Hospital M edical School (University of London), Cranmer Terrace, London S W I 7 ORE, UK bInstitute of Cytology, Russian Academy of Sciences, Tikhoretsky Avenue 4, 194064 St. Petersburg, Russian Federation (Received 15 October 1992; accepted 26 January 1993) Abstract The flow of electrolytes and non-electrolytes through narrow pores (about 1 nm radius) in synthetic membranes is reported. The characteristic features of such flow are the following. (i) The electrical conductivity displays fluctuations typical of single channel-like openings and closings. (ii) There is selectivity between anions and cations. (iii) The electrical conductance and flow of Rb+, Cl-, deoxyglucose or water is inhibited by the following ions in the order H+>Zn2+>Ca2’>Mg ‘+ The similarity of the behaviour between flow through such synthetic membranes and transport across biological membranes is noted, and its significance to biological phenomena is discussed. Keywords: Divalent cations; modulation; protons; surface flow; synthetic membranes. Introduction The flow of electrolytes or non-electrolytes through pores in biological membranes, which is induced by agents as varied as certain haemolytic viruses [l], bacterial [2,3] or animal [4] toxins, immune molecules [2,5,6] or detergents at sublytic concentration [4], shows properties that are remarkably similar from agent to agent. These include (a) inhibition by divalent cations, with a relative efficacy in the order Zn* + > Ca2 + > Mg2 + [7] and, (b) when the agents are incorporated into planar lipid bilayers with an applied voltage across them, fluctuations in the current typical of the “single channel” openings and closings of endoge- nous ion channels [S-lo]; in several of these *Corresponding author. ‘Present address: Dept. of Cellular & Molecular Sciences, St. George’s Hospital Medical School (University of London), Cranmer Terrace, London SW17 ORE, UK. systems, protons also inhibit flow (with relative efficacy H+ > Zn2+) [ll]. In an attempt to understand the basic mecha- nism that underlies these observations, we have studied the flow of electrolytes and non-electrolytes through purely synthetic membrane filters: we find that divalent cations and protons have the same effect and observe “single channel”-like fluctuations of the current, provided the membrane pores are narrow enough. We conclude that these effects are features of flow along any liquid-solid interface or channel wall, and can be observed whenever the contribution of bulk flow is minimised (as in the case of very narrow pores). Experimental Filters The filters (5 or 10 pm thick) were made of poly(ethylene terephthalate) (PETP). After heavy- 0927-7757/93/$06.00 0 1993 - Elsevier Science Publishers B.V. All rights reserved.