RESUMO
This study was undertaken to assess the localization of the Na+,K+-ATPase in the neuroepithelial cells of the macula sacculi. In vitro perilymphatic (basolateral) perfusion with ouabain produced a significant drop in the membrane potential. Endolymphatic (apical) application of ouabain had practically no effect on membrane potentials. This suggests that Na+,K+-ATPase is asymmetrically distributed in the neuroepithelial cells.
Assuntos
Máculas Acústicas/enzimologia , Sáculo e Utrículo/enzimologia , ATPase Trocadora de Sódio-Potássio/análise , Ambystoma mexicanum , Animais , Técnicas In Vitro , Potenciais da Membrana/efeitos dos fármacos , Ouabaína/farmacologia , Perilinfa/efeitos dos fármacosRESUMO
1. The macula sacculi in the mudpuppy is an inner ear sensory area accessible for intracellular recordings in vitro and in vivo. 2. The resting potentials recorded in vitro can be explained by the electrodiffusion theory assuming a uniform ionic selective in the membranes of the neuroepithelial cells. 3. The resting potentials recorded in vivo are significantly larger than predicted by the electrodiffusion theory, probably because of an electrogenic metabolic process present in the neuroepithelial cells. 4. An equivalent circuit is proposed to explain the resting electrogenesis in the neuroepithelial cells present in the sensory area.
Assuntos
Células Ciliadas Auditivas/fisiologia , Mecanorreceptores/fisiologia , Urodelos/fisiologia , Animais , Técnicas In Vitro , Cinética , Potenciais da Membrana/efeitos dos fármacos , Potássio/farmacologiaRESUMO
The optic nerve of Necturus maculosus consists of a homogeneous population of astroglia and bundles of unmyelinated axons. The glial cell processes ramify within the nerve roughly delineating fascicles of axons and come together at the periphery to form a complete external limiting membrane interrupted only by narrow clefts between adjacent processes. They are frequently "attached" to one another, forming specialized junctions. Blood vessels are entirely outside the nerve which is surrounded by a basal lamina. The temperature dependence of the glial membrane potential is accurately predicted by the Nernst relation. The membrane potential is unaffected by changes in Cl, Na, Li, and guanidinium which are apparently impermeant. The permeability of the glial membrane to other cations is in the sequence Tl greater than K greater than Rb greater than Cs greater than NH4. This suggests that the chemical nature of the site of potassium permeability in glial cells is similar to that in the neuron.
Assuntos
Astrócitos/ultraestrutura , Neuroglia/ultraestrutura , Nervo Óptico/citologia , Urodelos/anatomia & histologia , Animais , Astrócitos/fisiologia , Permeabilidade da Membrana Celular , Cloretos/metabolismo , Eletrofisiologia , Nervo Óptico/fisiologia , Potássio/metabolismo , TemperaturaAssuntos
Neuroglia/metabolismo , Neurônios/fisiologia , Nervo Óptico/metabolismo , Potássio/metabolismo , Animais , Cianetos/farmacologia , Fluorescência , Junções Intercelulares , Potenciais da Membrana , NAD/metabolismo , Neuroglia/efeitos dos fármacos , Nervo Óptico/citologia , Nervo Óptico/efeitos dos fármacos , Nervo Óptico/fisiologia , Fosforilação Oxidativa/efeitos dos fármacos , Potássio/farmacologia , UrodelosRESUMO
Ruthenium red and colloidal lanthanum were used to determine the site of the structural barriers to diffusion within the intercellular spaces of frog skin epithelium. Electron micrographs show that occluding zonules located at the outer border of the stratum corneum and at the outer layer of the stratum granulosum are true tight junctions since they are impermeable to these tracers. Measurement of (140)La uptake by the living skin shows that lanthanum moves across the external surface of the skin readily, into and out of a compartment that has a limited capacity and is bounded on its internal side by a barrier impermeable to lanthanum. Examination of these skins with the electron microscope suggests that the compartment is localized between the external membrane of the cells at the outer layer of the s. granulosum and at the outermost surface of the skin. These observations and other findings described in the literature indicate that the site of the external high resistance barrier of the frog skin is localized at the outer border of the s. granulosum.
Assuntos
Permeabilidade da Membrana Celular , Pele/metabolismo , Absorção , Animais , Anuros , Transporte Biológico , Membrana Celular/análise , Membrana Celular/fisiologia , Citoplasma/análise , Difusão , Células Epiteliais , Epitélio/metabolismo , Histocitoquímica , Junções Intercelulares/fisiologia , Lantânio/análise , Lantânio/metabolismo , Potenciais da Membrana , Colagenase Microbiana , Microscopia Eletrônica , Pressão , Radioisótopos , Rana pipiens , Rutênio/análise , Rutênio/metabolismo , Pele/citologiaAssuntos
Permeabilidade , Pele/citologia , Animais , Anuros , Lantânio/metabolismo , Microscopia Eletrônica , Rutênio/metabolismo , Pele/metabolismoRESUMO
1. The effects of varying the external Ca concentration from 1.8 to 30 mM/l. ((1/8)-2 times normal) have been studied at the in vitro crayfish excitatory neuromuscular junction. Electrophysiological techniques were used to record transmembrane junctional potentials from muscle fibres and extracellular junctional currents from the vicinity of nerve terminals.2. The excitatory junctional potential amplitude was proportional to [Ca](0) (n), where n varied between 0.68 and 0.94 (mean 0.82) when [Ca](0) was varied from 1.8 to 15 mM/l.3. The increase in junctional potential amplitude on raising [Ca](0) resulted primarily from an increase in the average number of quanta of excitatory transmitter released from the presynaptic nerve terminal by the nerve impulse.4. The size of the quanta, synaptic delay, presynaptic potential and electrical properties of the muscle membrane were little affected by changes in calcium concentration in the range studied.
