Channel molecule

DHP drugs bind allosterically. The open L-channel is somehat more permeable to the Ba ion than to the Ca ion but is very much less permeable to the Na ion. Nonetheless, because Na ion concentrations are so much higher than Ca ion concentrations, the actual fraction of charge carried by the two ions is not always so clear. There are a number of states that the L-channel can be in, aside from simply being open or closed. It is the distribution of L-channel molecules among the various states that is influenced by transmembrane voltage. From another view the rate constants between the states are functions of the transmembrane voltage. 

Facilitated diffusion (channel), molecule moves down its electrochemical gradient. Active transport (pump) molecule moves up its electrochemical gradient (requires energy input). Pumps use energy (usually ATP hydrolysis). Na+ high outside/K+ high inside. 

Agnew, W. S. Voltage-regulated sodium channel molecules. Annu. Rev. Biochem. 46, 517-530,1984. 

There are at least five different types of voltage-dependent Ca2+ channel molecules, differing in their gating kinetics, modes of Ca2+-inactivation and Ca2+-iregulation, and sensitivity to specific marine toxins [13] (see Ch. 6). The distinctions between the types of channel are of considerable interest because the different subtypes are believed to subserve different cellular functions. For example, the control of neurotransmitter release in peripheral sympathetic neurons appears to be under the predominant control of N-type calcium channels. 

Figure 18. (a) Transmembrane channel molecule 14 with 21 amino acid peptide composed of 15 i-leucines and 6 21 -crown-7-L-phenylalanine. (b) Axial projection of the helix, (c) Side view of the channel structure. ... 

Does thermal motion make a difference for this aspect of the structure of ice Figure lb shows a snapshot from a simulation at finite temperature, prior to melting. While the perfect molecular alignments of the ideal lattice have been lost, the picture still shows discernible channels molecules in solids do move, but this motion does not affect the overall symmetry. 

Aidley, D.J. Stanfield, P.R. (1996) Ion Channels Molecules in Action, Cambridge University Press, Cambridge. 

Calcium channel ai and p subunits are subject to further heterogeneity due to alternate splicing, thus giving rise to a potentially vast number of different types of calcium channel molecules whose expression and distribution may be dynamically regulated to suit a particular physiological function. It is important to bear this in mind when comparing native calcium channel currents to data obtained in transient expression systems. 

Figure 2a illustrates the concepts of radiative and nonradiative decay, fluorescence quantum yield, and fluorescence decay. A molecule in an excited electronic state can relax by several channels. Molecules excited to a vibrational level in the excited state undergo vibrational relaxation (cooling, yellow arrows in Fig. 2a) to the lowest vibrational levels of the excited state in a... 

The stochastic nature can be understood by certain energy barriers that must be overcome before a channel can flip from one conformation (e.g., open) to another (e.g., closed). The energy needed for this purpose comes from the random thermal energy of the system. One can imagine that each time the channel molecule vibrates, bends or stretches, it has a chance to surmount the energy barrier. Each motion is like a binomial trial with a certain probability of success. Clearly, because the protein movements are on a picosecond time scale, but the channel stays open for milliseconds, the chance of success at each trial must be small, and many trials will be needed before the channel shuts. Usually, a normal Na+ channel does not reopen even though the depolarization may be pertained by the... 

All patches with Na+ channels had both early and late channel openings, corresponding to peak and persistent Na+ currents. The persistent Na current was typically 0.5% of the peak current. The Na channel openings included both the brief late openings and the burst openings described in other neuronal (Alzheimer et al 1993) and muscle cells (Patlak Ortiz 1986), openings that are believed to represent different kinetic states of the same channel molecule (Moorman et al 1990). The burst openings were seen in far less than 1% of pulses, and in some patches were not seen at all. 

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