Membrane potential action

ACTION POTENTIAL MEMBRANE POTENTIAL ACTION SPECTRUM Activated cluster,... 

PERMEABILITY PERMEABILITY CONSTANT MEMBRANE POTENTIAL ACTION POTENTIAL DEPOLARIZATION GOLDMAN EQUATION NERNST EQUATION RESTING POTENTIAL THRESHOLD POTENTIAL PATCH-CLAMP TECHNIQUE Membrane protein dynamics,... 

ABSTRACT Electrical phenomena in artificial cells are described. The constituent material of the cells, referred to as proteinoid or as thermal protein, have been extensively studied in the context of the origin of life, which led to the finding of excitability as one of the biofunctions. The activities found in proteinoid cells are such as to make them useful models for modern excitable cells as well as for protocells. For example, the proteinoid cells display double membrane, asymmetric permeability, membrane potentials, action potentials, and photoactivity. 

The demonstration of GABA receptors coupled to Cl channels in the posterior pituitary (Zhang and Jackson 1993) prevailed Zhang and Jackson (1995) by activation of these receptors and gating the Cl channels to alter membrane potential, action potentials, and the status of voltage-gated channels. Their results supported a depolarisation block mechanism in the inhibition of secretion by GABA. 

Other auxin-like herbicides (2,48) include the chlorobenzoic acids, eg, dicamba and chloramben, and miscellaneous compounds such as picloram, a substituted picolinic acid, and naptalam (see Table 1). Naptalam is not halogenated and is reported to function as an antiauxin, competitively blocking lAA action (199). TIBA is an antiauxin used in receptor site and other plant growth studies at the molecular level (201). Diclofop-methyl and diclofop are also potent, rapid inhibitors of auxin-stimulated response in monocots (93,94). Diclofop is reported to act as a proton ionophore, dissipating cell membrane potential and perturbing membrane functions. 

An Action Potential is a stereotyped (within a given cell) change of the membrane potential from a resting... 

Repolarization is a return of membrane potential to its resting value. It refers mostly to repolarization of an action potential, although a more general meaning of returning a membrane potential back to a more negative value after (forced) depolarization is also common. 

Resting potential is a stable membrane potential in nonexcitable cells, or the most stable membrane potential between Action Potentials in excitable cells. In some excitable tissues it is impossible to define a resting potential because of continuous change in membrane potential. 

Voluntary muscle contraction is initiated in the brain-eliciting action potentials which are transmitted via motor nerves to the neuromuscular junction where acetylcholine is released causing a depolarization of the muscle cell membrane. An action potential is formed which is spread over the surface membrane and into the transverse (T) tubular system. The action potential in the T-tubular system triggers Ca " release from the sarcoplasmic reticulum (SR) into the myoplasm where Ca " binds to troponin C and activates actin. This results in crossbridge formation between actin and myosin and muscle contraction. 

Sea urchin toxins extracted from spines or pedicellariae have a variety of pharmacological actions, including electrophysiological ones (75). Dialyzable toxins from Diadema caused a dose-dependent increase in the miniature end-plate potential frequency of frog sartorius muscle without influencing membrane potential (76). A toxin from the sea urchin Toxopneustes pUeolus causes a dose-dependent release of histamine (67). Toxic proteins from the same species also cause smooth muscle contracture in guinea pig ileum and uterus, and are cardiotoxic (77). 

Figure 1.4 Ionic basis for excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). Resting membrane potential ( — 70 mV) is maintained by Na+ influx and K+ efflux. Varying degrees of depolarisation, shown by different sized EPSPs (a and b), are caused by increasing influx of Na. When the membrane potential moves towards threshold potential (60-65 mV) an action potential is initiated (c). The IPSPs (a b ) are produced by an influx of Cl. Coincidence of an EPSP (b) and IPSP (a ) reduces the size of the EPSP (d)...

Identity of action. The proposed NT must produce effects postsynaptically which are identical physiologically (appropriate membrane potential changes) and pharmacologically (sensitivity to antagonists) to that produced by neuronal stimulation and the relased endogenous NT. 

Figure 1.9 Comparison of the effects of an endogenously released and exogenously applied neurotransmitter on neuronal activity (identity of action). Recordings are made either of neuronal firing (extracellularly, A) or of membrane potential (intracellularly, B). The proposed transmitter is applied by iontophoresis, although in a brain slice preparation it can be added to the bathing medium. In this instance the applied neurotransmitter produces an inhibition, like that of nerve stimulation, as monitored by both recordings and both are affected similarly by the antagonist. The applied neurotransmitter thus behaves like and is probably identical to that released from the nerve...

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