The Use of Radioisotopes to Characterise the Abnormal Permeability of Red Blood Cells from Sickle Cell Patients

Abstract

1.1 Membrane transport and radioisotopes In order to function, cells of necessity must transport a variety of substances across their plasma membranes. Aside from simple non-polar entities, most of these will require the presence of special transport proteins. Radioisotopes, used as tracers for these substrates, have provided an invaluable tool for understanding the mechanism and regulation of such transport pathways. In this chapter, we will cover some theoretical and practical issues concerning the measurement of transport with radioactive tracers. As an illustration, we will focus on membrane transport in red blood cells, a tissue much used in the study of membrane permeability. In particular, we will look at the abnormal cation permeability of red blood cells from sickle cell patients to show how radioactive tracer methodologies can be used to investigate the pathophysiology of membrane permeability. Chemical analysis of transport is feasible, but can often be tedious and slow. That by radioactive tracers has the advantage of being relatively immediate whilst retaining comparative simplicity. The first artificial radioisotopes were produced by Curie and Juliot in 1934 when they synthesised phosphorus-30 by exposure of aluminium-27 to Ǐ particles. Over the next 50 years or so, numerous different radioisotopes became available and were widely used to follow transport across biological membranes. Seminal examples include the use of 24Na+ to investigate active Na+ transport across the giant axon of cuttlefish in the mid 1950s (Hodgkin & Keynes, 1955a, 1955b; as elegantly retold by Boyd, 2011, following Keynes’ death last year). The perceptive analysis of these studies underpinned the hypothesis and identification of the Na+/K+ pump by Skou, Post, Jolly and colleagues (Skou, 1957; Post & Jolly, 1957; Glynn, 2002; Skou, 2003), whilst in the late 1960s onwards Glynn and colleagues also used 24Na+ and 42K+ to study the pump (Garrahan & Glynn, 1967) and especially the existence of occluded ions (Glynn et al., 1984; Glynn, 2002). With more recent methodogical advances and the more restrictive practices surrounding use of radioactive compounds, other non-radioactive methods (such as ion-sensitive