Ion channels in membranes

The development of biophysical techniques to make possible measurements of single ion channels in membrane bilayers has been fundamental to the advances in the understanding of how natural ionophores, particularly ion channel proteins, operate at the molecular level. The two principal techniques are the planar lipid... 

Urry, D. W. On the Molecular Structure and Ion Transport Mechanism of the Gramicidin Transmembrane Channel. In Membranes and Transport, Vol. 2, (ed. Martonosi, A.), p. 285, Plenum Publishing Corporation, New York 1982... 

The patch-clamp technique is based on the formation of a high resistance seal (109-10lon) between the tip of a glass micropipette and the cell membrane it touches (gigaohm-seal). This technique allows recordings of ionic currents through single ion channels in the intact cell membrane and in isolated membrane patches at a... 

In a different context, a micropipette has been applied to monitor the current through a single-ion channel in a biological membrane. The patch-clamp technique invented by Sackmann and Neher [119] led to their Nobel Prize in medicine. The variations in channel current with voltage, concentration, type of ions, and type of channels have been explored. While the functions of specific channels, in particular their ionic selectivity, have been well known, only a handful of channels have the internal geometry and charge distribution determined. The development of a theory to interpret the mass of channel data and to predict channel action is still lacking. 

Marine toxins modify the functions of many different types of ion channels in animal cell membranes. These channels may be important for maintaining the cell s resting potential, for generating electrical membrane signals, such as impulses, and for controlling hormonally triggered or metabolic responses. Thus toxins may depolarize membranes, leading to a (sometimes transient) increase in cellular activities, or they may... 

It has been known for some years that gramicidin forms transmembrane ion channels in lipid bilayers and biological membranes and that these channels are assembled from two molecules of the polypeptide 213). The channels are permeable specifically to small monovalent cations [such as H+, Na+, K+, Rb+, Cs+, Tl+, NH4+, CHjNHj, but not (CH3)2NH2+J and small neutral molecules (such as water, but not urea). They do not allow passage of anions or multivalent cations 21 n. 

The opening of masses of ion channels in nematode muscle membranes may be detected using the two-microelectrode voltage-clamp technique. In contrast, the opening of single ion channels may be recorded using the vesicle preparation and patch-clamp technique. These techniques are both described below. 

Under basal conditions, PKC is predominantly a cytoplasmic protein. Upon activation by Ca2+ or DAG, the enzyme associates with the plasma membrane, the site of many of its known physiological substrates, including receptors and ion channels. In fact, the translocation of PKC from the cytoplasm to the membrane has long been used as an experimental measure of enzyme activation. Such translocation has often been assayed by phorbol ester binding phorbol esters are tumor-promoting agents that selectively bind to and activate PKC. The molecular basis of the translocation of PKC from the cytoplasm to the plasma membrane has been solved. Subsequent to activation, PKC binds with high affinity to a series of membrane-associated proteins, termed receptors for... 

Mechanisms that may contribute to synchronous hyperexcitability include Alterations of ion channels in neuronal membranes... 

In smooth muscle, the sarcoplasmic reticulum (SR) plays an important role in regulating cell excitability by communicating intimately with ion channels in the surface membrane. In most cases, Ca2+ release from ryanodine-sensitive Ca2+ release channels (RyRs) in the SR leads to a paradoxical decrease in smooth muscle cell excitability due to activation of plasma membrane K+ channels (Fig. 1 Nelson et al 1995). This is in stark contrast to cardiac muscle, where Ca2+ release from RyRs supplies the majority (> 90%) of Ca2+ required for contraction (Cheng et al 1993, Cannell et al 1995). In this paper, we will briefly review the basic... 

To date, all smooth muscle types examined display characteristic Ca2+ release events known as Ca2+ sparks (Fig. 1 see Jaggar et al 2000 for review). Ca2+ sparks are localized Ca2+ release events through RyRs in the SR located very close (10—20nm) to the surface membrane. Ca2+ sparks can activate Ca2+ -dependent ion channels in the cell surface, and the physiological response of the particular cell type will reflect the type of ion channels involved (Fig. 1). 

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