Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-1855, USA.Current Biology (Impact Factor: 9.57). 05/2006; 16(8):R272-6. DOI: 10.1016/j.cub.2006.03.050
Membrane biophysics is a vast field, in which life uses all of the physical forces and laws to organize physiological processes. The simple physics of the phospholipid bilayer often dominates the structure of the membrane to provide compartmentalization of cellular space - proteins work within the constraints of the bilayer to catalyze lipid metabolism, bend membranes, transport impermeant substances, organize microdomains, and many other essential processes of life.
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ABSTRACT: Membrane voltage “noise” produced by adenosine 5'-triphosphate (ATP) in smooth muscle cells has been analyzed to infer the properties of individual ATP-activated membrane ionic channels and compare these with the kinetics of the quantal synaptic potential in smooth muscle, the spontaneous excitatory junction potential. (sEJP). Pressure application of ATP (10 μM in Krebs solution) for 10-30 seconds through a micropipette, but not application of Krebs alone, produced steady, low-amplitude membrane depolarizations accompanied by an increase in membrane voltage noise. Spectral noise analysis yielded a channel mean open time (m.o.t) for ATP-activated channels of 45.7±4.5 ms at 37°C. The decay time constant of SEJPs under similar conditions was 42.2±18.3 ms. This was not significantly different (P>0.05) compared with the m.o.t. of ATP-activated channels. By analogy with other synapses, it is concluded that ATP produces channel activations in smooth muscle consistent with its mediation of sEJPs. The authors' analysis suggests the amplitude of the elementary depolarization to be ~20-30 μV, thus the number of ATP-activated channels underlying typical sEJPs of amplitude 3-12 mV may be approximately 100-500. These findings are discussed in relation to the microphysiology of operation of the autonomic nerve-smooth muscle synapse
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ABSTRACT: This chapter discusses the photosynthetic pigment–protein complexes in planar lipid membranes. The photosynthetic pigment–protein complexes may be classified into two separated and functionally distinctive classes: reaction centers (PS II, PSI and BRC) and light harvesting complexes (such as the largest light- harvesting complex of PS II, LHCII). Major part of research on photosynthetic pigment–proteins carried out with the application of model planar lipid membranes concerns the electron flow across the reaction centers, in particular BRC. The fact that the membrane separated two water bulk phases containing cytochrome c and ubiquinone, the secondary electron donors and acceptors to BRC, respectively, enabled the observation of light-induced electric current and voltage across the protein—containing membrane. The wavelength dependence of the photoresponse matched the absorption spectrum of reaction centers, which is a proof of functional reconstitution of the protein complex. The main physiological function of photosynthetic antenna complexes, such as LHCII, is harvesting light quanta and transferring excitation energy toward the reaction centers. According to the current knowledge these pigment–proteins are not directly involved in the linear or cyclic photosynthetic electron transfer in the thylakoid membranes.