Potential dependent channels schematic

A schematic representation of Na+ channels cycling through different conformational states during the cardiac action potential. Transitions between resting, activated, and inactivated states are dependent on membrane potential and time. The activation gate is shown as m and the inactivation gate as h. Potentials typical for each state are shown under each channel schematic as a function of time. The dashed line indicates that part of the action potential during which most Na+ channels are completely or partially inactivated and unavailable for reactivation. 

Figure 5. Schematic illustration of the energy dependence of the channel phase in different simple limits of Eq. (43), along with the corresponding potential energy curves. See Section IVC. (Reproduced with permission from Ref. 43, Copyright 2001 American Chemical Society.)...

Schematic diagram of a generalized noradrenergic junction (not to scale). Tyrosine is transported into the noradrenergic ending or varicosity by a sodium-dependent carrier (A). Tyrosine is converted to dopamine (see Figure 6-5 for details), which is transported into the vesicle by a carrier (B) that can be blocked by reserpine. The same carrier transports norepinephrine (NE) and several other amines into these granules. Dopamine is converted to NE in the vesicle by dopamine-B-hydroxylase. Release of transmitter occurs when an action potential opens voltage-sensitive calcium channels and increases intracellular calcium. Fusion of vesicles with the surface membrane results in expulsion of norepinephrine, cotransmitters, and dopamine-13-hydroxylase.

Figure 3. Schematic architecture of mitochondrial protein complexes. A transmembrane channel, called the permeability transition pore (FTP), is formed at the contaa sites between the inner and outer mitochondrial membrane (OM) of the mitochondria. The core components of PTP are the voltage-dependent anion channel (VDAC) in the outer membrane and the adenine nucleotide translocator (ANT) in the inner membrane (IM). VDAC allows diilusion of small molecules (<5 kDa), however ANT is only permeable to a few selected ions and metabolites and is responsible for maintaining the proton concentration gradient (pH) and the membrane elearic potential (A P,J. PTP is sometimes connected to destruction of permeability barrier and loss of the inner membrane potential and eventually results in mitochondrial membrane permeability transition during apoptosis and other specialized forms of cell death. Bax, Bak, Bc1-Xl and Bcl-2 locate in the outer membrane and may regulate the outer membrane permeability. The translocase of the outer membrane (TOM) and the translocase of the inner membrane (TlM) mediate protein import pathway in the mitochondria. Cy-D, cyclophilin D PBR, peripheral benzodiazepine receptor HK, hexokinase mtHSP70, mitochondrial heat shock protein 70.

Earlier sections of this chapter have illustrated potentiometric methods for the selective determination of ions and molecules. An alternative, elegant, more recent adaptation in which the currents flowing in tiny field effect transistors (FETs) can be used to probe ion concentrations is shown schematically in Fig. 5.8. The FET is made of n-p-n semiconductors which form respectively the source, channel and the drain. In a conventional FET the current flowing between the source and the drain is influenced by a voltage applied to the (metallic) gate (Fig. 5.8). In an ISFET an ion-selective membrane acts as the gate instead of a metal and the electrical potential it exerts on the source-to-drain current depends on the extent to which substrate ions have entered the membrane. The current therefore measures the ionic concentrations. Typical ion-membrane combinations for use in ISFETs are... 

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