Abstract

Ion channels belong to a class of integral membrane proteins, which when confronted with a stimulus, are able to change their conformation from a nonconductive to an ion-conductive one or vice versa. This chapter describes the surface charge effects on ion conduction in ion channels. A charged surface in the neighborhood of the ion conduction system influences the concentration of ions at the channel entrances and hence, its conductance. In biological membranes, fixed charges can originate in principle from three different sources: (1) the membrane lipids, (2) ionized groups in the channel-forming protein, and (3) nonprotein domains forming part of the molecular structure of the channel, such as acidic carbohydrate domains containing sialic acid. The most abundant charged phospholipid in biological membranes is phosphatidylserine (PS), which possesses a single negative charge from the carboxyl group in the serine residue of the lipid. Channel blockade by ions can be used to obtain an independent estimation of the surface charge of the vestibules.