Membrane Pores

Abstract

Every cell in the body is surrounded by a narrow membrane that consists of lipids and proteins. The lipids provide insulation from the external environment, while the proteins play an opposite role: they sense the environment and transmit information to the interior of the cell. In many cases, the signals are transmitted through narrow pores across the membrane; the propagation of impulses in nerves and the contraction of muscles are examples. Different types of protein make different kinds of pores: some for the passage of specific inorganic ions like K+, Na+, and Ca2+, and others for the passage of organic nutrients, like glucose and amino acids.

Membrane pores across the cell membrane are also induced by a variety of toxic agents. In this case, the pores are non-specific, and the outcome is detrimental to the life of the cell, since essential ions and molecules leak out. Agents as diverse as viruses, bacterial and animal toxins, low concentrations of detergents, and other molecules cause such pores to be formed. We have found that these types of pores have certain properties in common. One is that pores are closed by divalent cations; the action of zinc in this regard may play a role in fighting off infections caused by some viruses and bacteria. Another property is that if a voltage difference is applied across the pore, current does not flow continuously but oscillates between high and low conductance states. Such fluctuations of current are typical also of the endogenous ion channels for K+, Na+, and Ca2+, mentioned above.

In order to better understand the nature of these effects, we have studied pores created across synthetic membranes made of organic polymers like polyethyleneterephthalate (PETP). Surprisingly, these too show fluctuations of current and inhibition by divalent cations. Such results provide new insights into the mechanisms underlying the flow of ions and molecules through biological membrane pores. They also open up the possibility of using synthetic membranes in various novel situations.