Electrical Properties Of Cells Research Articles

Potassium channels and vascular proliferation

Potassium channels are currently the focus of much attention because of their recently discovered role in the regulation of vascular smooth muscle growth. Dramatic alterations in the expression and activity of K+ channels causing marked changes in the cell's electrical properties accompany enhanced growth of smooth muscle cells (SMCs). These findings indicate that alterations in K+ channel function are important for SMC proliferation. However, the mechanisms by which changes in K+ channel activity influence cellular growth pathways are poorly understood. The emergent electrical properties caused by modulation of K+ channels are associated with marked differences in the spatial and temporal organization of Ca2+ signaling. Thus, changes in K+ channel function may represent a universal mechanism by which Ca2+ signals are targeted towards activation of gene expression and cell growth. As enhanced growth of smooth muscle underlies many cardiovascular diseases and clinical pathologies, the identification of an important role for K+ channels in SMC proliferation indicates a new source of therapeutic targets to regulate proliferative vascular disorders.

Effects of deafferentation on the electrophysiology of ventral cochlear nucleus neurons

When cochlear pathology impairs the afferent innervation of the ventral cochlear nucleus (VCN), electrical responses of the auditory brainstem are altered and changes in cell and synaptic morphology are observed. However, the impact of deafferentation on the electrical properties of cells in the VCN is unknown. We examined the electrical properties of single neurons in the anterior and posterior VCN following bilateral cochlear removal in young rats. In control animals, two populations of cells were distinguished: those with a linear subthreshold current–voltage relationship and repetitive firing of action potentials with regular interspike intervals (type I), and those with rectifying subthreshold current–voltage relationships and phasic firing of 1–3 action potentials (type II). Measures of action potential shape further distinguished these two groups. Two weeks following cochlear removal, both electrical response patterns were still seen. Type I cells showed a higher input resistance. Deafferented single-spiking type II cells were slightly more depolarized, had smaller action potentials, smaller afterhyperpolarizations and shorter membrane time constants, whereas multiple-spiking type II cells were apparently unaffected. These changes in the electrical properties of VCN neurons following cochlear injury may adversely affect central processing of sounds presented acoustically or electrically by prostheses.

Developmental switch in excitability, Ca(2+) and K(+) currents of retinal ganglion cells and their dendritic structure.

In the retina of teleost fish, continuous neuronal development occurs at the margin, in the peripheral growth zone (PGZ). We prepared tissue slices from the retina of rainbow trout that include the PGZ and that comprise a time line of retinal development, in which cells at progressive stages of differentiation are present side by side. We studied the changes in dendritic structure and voltage-dependent Ca(2+), Na(+), and K(+) currents that occur as ganglion cells mature. The youngest ganglion cells form a distinct bulge. Cells in the bulge have spare and short dendritic trees. Only half express Ca(2+) currents and then only high-voltage-activated currents with slow inactivation (HVAslow). Bulge cells are rarely electrically excitable. They express a mixture of rapidly inactivating and noninactivating K(+) currents (IKA and IKdr). The ganglion cells next organize into a transition zone, consisting of a layered structure two to three nuclei thick, before forming the single layered structure characteristic of the mature retina. In the transition zone, the dendritic arbor is elaborately branched and extends over multiple laminae in the inner plexiform layer, without apparent stratification. The arbor of the mature cells is stratified, and the span of the dendritic arbor is well over five times the cell body's diameter. The electrical properties of cells in the transition and mature zones differ significantly from those in the bulge cells. Correlated with the more elaborate dendritic structures are the expression of both rapidly inactivating HVA (HVAfast) and of low-voltage-activated (LVA) Ca(2+) currents and of a high density of Na(+) currents that renders the cells electrically excitable. The older ganglion cells also express a slowly activating K(+) current (IKsa).

Dendrites of classes of hippocampal neurons differ in structural complexity and branching patterns

Dendrites of reconstructed hippocampal neurons were analyzed for morphometric, topologic, and fractal parameters (n = 32 quantities) to investigate neuronal groupings and growth characteristics with a common set of assumptions. The structures studied included CA1 and CA3 pyramidal cells, interneurons, and granule cells from young animals (71 cells in total). Most of the cells showed no characteristic fractal dimension; rather, the scaling relation could be well represented by a two-parameter fit, of which one parameter showed a significant difference between cell classes. Other significant quantities that differentiated cell classes were related to the complexity of the dendritic tree (number of branch points and maximal terminal branch order) and the cell's electrical properties such as the mean attenuation between the soma and terminals. Principal components analysis produced combined measures of only slightly greater discriminative power than the best individual measures, indicating that the elementary quantities capture most of the structural variation between hippocampal cell groups. Another finding was that for all cells the mean segment length increased with dendritic branch order, which is consistent with decreasing branching probability as a function of the path distance from the soma. Analysis of another set of CA1 pyramidal neurons from aged animals (n = 15; 22-24 months) showed only a few significant differences than those from young animals (n = 11; a subset of n = 71) of which the most important was a straightening of the paths between terminals and the soma. The quantities analyzed in these reconstructed hippocampal neurons may reflect both intrinsic neuronal characteristics and extrinsic influences. Hippocampal cell groupings (i.e., pyramidal cells as opposed to dentate granule cells and interneurons) were significantly differentiated by most parameters. These differences and parameter values may be critical for understanding and generating synthetic neuronal populations for modelling studies.

Electrical Properties of Cells: Patch Clamp for Biologists.Louis J. DeFelice

Previous articleNext article No AccessNew Biological BooksElectrical Properties of Cells: Patch Clamp for Biologists. Louis J. DeFelice Edwin S. LevitanEdwin S. Levitan Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 73, Number 4Dec., 1998 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/420449 Views: 2Total views on this site Copyright 1998 The University of ChicagoPDF download Crossref reports no articles citing this article.

Electrical Properties of Cells (Patch Clamp for Biologists)

Electrical Properties of Cells (Patch Clamp for Biologists)

An alternative method for the analysis of neuron passive electrical data which uses integrals of voltage transients

The traditional method for analyzing passive electrical data from neurons when specific morphological data are unavailable consists of decomposing the voltage response of the cell into a series of exponential functions (the peeling method) and substituting the time constants of these exponential functions into equations derived from cable theory (Rall W, Core conductor theory and cable properties of neurons. In: Handbook of Physiology. The Nervous System. Cellular Biology of Neurons. Bethesda, MD. Am Physiol Soc. Section 1, Part 1, 1977;1(3):39–97). In the present report, an alternative method is examined for analyzing these kinds of data, the integrals of transients method (Eisenberg RS, Mathias RT. Structural analysis of electrical properties of cells and tissues. CRC Critical Reviews in Bioengineering 1980;4:203–232). The integrals required are easily obtained from input resistance data and any theoretical model that is appropriate for the neurons under study can be used, provided that the impedance function can be determined. In order to demonstrate this alternative method, a simple 3-compartment model with both dendritic taper and somatic shunt is used to model data obtained from fast-type α-motoneurons in the spinal cord of the cat. These results are compared with results obtained using the traditional peeling method. This comparison indicates that passive electrical data from fast-type motoneurons are best analyzed using a theoretical model that includes both dendritic taper and somatic shunt. Furthermore, our results show that the integrals of transients method can facilitate this analysis.

Electrical properties of neocortical neurons in slices from children with intractable epilepsy

1. The intrinsic electrical properties of human neocortical neurons were studied with current-clamp and single-electrode voltage-clamp techniques in slices obtained from children, aged 3 mo to 15 yr, undergoing surgical treatment of intractable epilepsy. Neocortical samples were classified as most or least abnormal based on clinical data. Recorded neurons were labeled with biocytin for correlation of electrical properties with morphological characteristics and laminar position. All recorded neurons were divided into three cell types--fast-spiking, low-threshold spiking (LTS) and non-LTS cells--on the basis of their electrical characteristics. 2. Fast-spiking cells generated brief, rapidly repolarizing action potentials. Most of these cells showed only weak spike-frequency adaptation. Fast-spiking cells labeled with biocytin were aspiny or sparsely spiny nonpyramidal neurons located in cortical layers 2-4. 3. LTS cells generated Ca(2+)-dependent low-threshold potentials and were the most numerous of the three cell types. Their Na(+)-dependent action potentials were broader than those of fast-spiking cells and showed marked spike-frequency adaptation. The size of low-threshold Ca2+ potentials and currents varied across cells, but they never supported more than two or, occasionally, three fast action potentials. LTS cells were pyramidal neurons located throughout cortical layers 2-6. Unlike the bursting neocortical cells described in lower mammals, LTS neurons in neocortex from children failed to generate bursts of inactivating Na+ action potentials. 4. Non-LTS cells also had relatively broad Na(+)-dependent action potentials and showed spike-frequency adaptation, but they did not generate detectable low-threshold potentials or currents. Non-LTS cells were also pyramidal neurons located throughout layers 2-6. 5. The electrical properties of cells from different age groups (< or = 1, 2-8, and 9-15 yr) and from most-abnormal and least-abnormal tissue samples were compared. A statistically significant trend toward a lower input resistance, a faster membrane time constant, and a decreased spike duration was observed with increasing age. There were no significant differences between the electrical properties of cells from the most-abnormal tissue and cells from the least-abnormal tissue. 6. These data indicate that the intrinsic electrical properties of neocortical neurons from children vary according to cell morphology and change with increasing age, as has been observed in rodent and feline neocortical neurons. No obvious evidence of epileptogenicity was detected in the intrinsic electrical properties of any of the neurons studied.

Biology of Blood Vessels in Hypertension

Increased peripheral vascular resistance is the hemodynamic characteristic of essential hypertension and is associated with structural and functional changes in resistance vessels. The major structural alterations constitute reduced vessel lumen diameter with thickening of the vascular wall. Only a 10% narrowing of the vessel lumen and a slight thickening of the vessel wall, which includes the medial and intimal layers, are sufficient to significantly increase peripheral resistance. At the cellular level, there is a significant increase in cell mass and collagen and elastin deposition with vascular smooth muscle hypertrophy and hyperplasia. Direct hemodynamic forces, as well as circulating and local growth regulators, stimulate cell growth in hypertensive vessels. Functional alterations that increase peripheral resistance include enhanced vascular reactivity to vasoconstrictor agents or impaired relaxation and reflect changes in excitation-contraction coupling and/or electrical properties of cells. Excess systemic or local production of vasoconstrictors or growth factors, abnormal agonist-receptor interactions, increased cell membrane permeability, defective transmembrane ion transport, intracellular calcium overload, exaggerated responses of the phosphoinositide signaling system, and altered endothelial function result in increased vascular smooth muscle growth and contractility. Whether these changes are a primary cause or secondary consequence of hypertension remains unclear but is a major focus of investigation. (Cardiol Rev 1993;1:2, 87-96)

Chaotic states in a random world: Relationship between the nonlinear differential equations of excitability and the stochastic properties of ion channels

Excitable membranes allow cells to generate and propagate electrical signals. In the nervous system these signals transmit information, in muscle they trigger contraction, and in heart they regulate spontaneous beating. A central question in excitability theory concerns the relationship between the aggregate properties of membranes (marcoscopic) and the properties of channels in the membranes (mircoscopic). Hodgkin and Huxley (1952) laid the foundations of membrane excitability, and Neher and Sakmann (1976) developed techniques to study individual channels. This article focuses on the relationship between the macroscopic domain, in which non-linear differential equations determine the electrical properties of cells, and the microscopic domain, in which the probabilistic nature of channels establishes the pattern of activity. Using nerve cell membranes as an example, we examine how information in one domain predicts behavior in the other. We conclude that the probabilistic nature of channels generates virtually all macroscopic electrical properties, including resting potentials, action potentials, spontaneous firing, and chaos.

Fractionation of erythroblasts with affinity-mediated modifications of their electrical properties using counter-current distribution.

We have previously reported the possibility of modifying the electrical properties of cells by means of their interaction with a specific ligand carrying a polyelectrolyte (Anal Biochem 200: 280-285). This selective modification of receptor-containing cells changed their partition in a charge-sensitive aqueous two-phase system. We here present the fractionation of electrically modified erythroblasts by the use of an automatic multiple-partition procedure, counter-current distribution. The cells were fractionated according to the degree of differentiation of erythroblasts as evaluated from the hemoglobin content as well as the relative activities of the two enzymes, 3-phosphoglycerate kinase and bisphospho-glycerate mutase.

Developmental changes and second messenger modulation of the electrical properties of cells of the cockroach corpora allata

The duration of evoked action potentials in the cells of the corpora allata of recently emerged adult mated female cockroaches was dramatically increased following replacement of calcium ions by barium ions in the bathing saline. The magnitude of this increase was age-dependent. Furthermore, following exposure of corpora allata to barium, spontaneous action potentials (approx. 10–40 mV in amplitude) and small depolarizing potentials (approx. 2–5 mV in amplitude) were observed that were never seen in the absence of barium. This suggests that barium increases the excitability of the corpora allata. 8-bromo-cyclic AMP and the phorbol ester, phorbol 12,13-dibutyrate (PDBu), both increased the duration of barium action potentials in corpora allata from day-1 and day-6 females. However, 8-bromo-cyclic GMP, and the nonspecific protein kinase inhibitor H7 both reduced the barium action potential in day-1 corpora allata but had no significant effect in day-6 corpora allata. Furthemore, the inactive phorbol ester 4a-phorbol 12,13-didecanoate (PDD) did not significantly affect the barium action potential duration in day-1 or day-6 corpora allata, suggesting that PDBu is acting through phospholipid/calcium-dependent protein kinase C and not nonspecifically. 8-Br-cAMP and protein kinase C appear to modulate the electrophysiological properties of the cell membranes of the corpora allata, which suggests that they may modulate calcium influx. In addition, cAMP, protein kinase C and calcium have previously been implicated in the regulation of juvenile hormone biosynthesis. In view of the effects of cAMP and protein kinase C on both membrane properties and juvenile hormone biosynthesis, the cell membrane may be a site for integration of the calcium, cAMP and protein kinase C second messenger systems involved in the regulation of juvenile hormone biosynthesis. Furthermore, because juvenile hormone biosynthesis undergoes cyclical changes in adult mated female cockroaches and there are developmental changes in the electrical properties of the corpora allata, such changes may be important in the regulation of juvenile hormone biosynthesis, possibly by altering calcium influx.

Cellular organization and development of slice cultures from rat visual cortex

Slice cultures from the visual cortex of young rats were prepared using the roller culture technique (Gähwiler 1984). After 10 days in vitro the cortical cultures flattened to 1-3 cell layers, surviving for up to 12 weeks. The cultures were organotypically organized, the typical layered structure of the cortex was preserved. The neuronal composition of slice cultures was studied using intracellular staining, Golgi impregnation and GABA immunohistochemistry. Both pyramidal cells and several types of nonpyramidal cells were identified in the slice cultures. Electrophysiological recordings showed that the electrical properties of cells in culture were similar to those measured in acute slice preparations; for some cells, however, the spontaneous activity was higher. The maintained activity was strongly increased by application of the GABA antagonist bicuculline and decreased by GABA, suggesting that GABAergic inhibition is present in these preparations. We could observe the postnatal maturation of some characteristic morphological features in culture. For example, pyramidal cells in 6 day-old rats in situ have very short basal dendrites with growth-cones, and the dendrites are free of spines. After 2-3 weeks in culture growth-cones were no longer observed. Instead, the cells had developed a large basal dendritic field and the dendrites were covered with spines. Slice cultures therefore may provide a useful tool for physiological, anatomical, pharmacological and developmental studies of cortical neurons in an organotypical environment.

Elevated glucose alters paracellular transport of cultured human proximal tubule cells

Cultures of human proximal tubule cells were exposed to elevated concentrations of glucose and dome formation was assessed over a 22 day period of growth. Cultures grown on 5.5 mM glucose formed five domes per microscopic field while those exposed to elevated glucose concentrations (11.0 mM to 27.5 mM) formed only two to three domes per field. The areas of the domes formed by the cells grown on elevated glucose concentrations were reduced as compared to those formed on 5.5 mM glucose. An analysis of the electrical properties of cells grown on elevated glucose concentrations by Ussing chamber technique disclosed a marked reduction in potential difference, short circuit current, and resistance compared to cells grown on 5.5 mM glucose. Routine ultrastructural analysis disclosed that cells grown on elevated glucose concentrations appeared to have fewer tight junction complexes. Further examination utilizing freeze fracture methodology demonstrated that cells grown on elevated glucose concentrations averaged two to three sealing strands per junction as compared to an average of five sealing strands for cells grown on 5.5 mM glucose. The cells grown on elevated glucose concentrations were also noted to possess a greater number of gap junctions. These results demonstrate that elevated glucose concentrations can alter the paracellular route, and possibly the transcellular route, of transport regulation in cultured human proximal tubule cells.

Electrophysiological Responses of Rat Pituitary Cells in Somatotroph-Enriched Primary Culture to Human Growth-Hormone Releasing Factor

The in vitro effects of human growth hormone releasing factor (hGRF, 1-44) were studied in somatotroph-enriched cultures (75-85%) obtained from adult male rat pituitaries. Cells perifused with hGRF showed an up to 800% increase in growth hormone (GH) release over basal values in a dose-dependent manner. Calcium current blockers (5 mM of Co2+, Ni2+ or Cd2+) completely inhibited this stimulating effect but sodium-free (choline) medium did not. Using a single-intracellular-electrode recording technique, it was found that hGRF induced a dose-dependent depolarizing response concomitant with a decrease in membrane resistance in 38% of the cells recorded (98 of 258 cells). The reversal potential of this response was close to -40 mV. This depolarizing response was recorded in both excitable and unexcitable cells with no marked difference. Co2+ and Ni2+ (5 mM) completely and reversibly inhibited the membrane response to hGRF. Application of hGRF and somatostatin (SRIF), a hormone that inhibits GH release, to the same cell cultures showed the existence of two subpopulations: one was responsive to both hGRF and SRIF (53%, n = 62), another was only responsive to SRIF (47%, n = 62). Human GRF did not affect prolactin release and did not modify the electrical properties of cells responding to dopamine and therefore considered as lactotrophs. These results suggest that (1) hGRF leads to an increase in growth hormone release and a modification of membrane electrical properties by means of an extracellular Ca2+-dependent pathway, and (2) according to their responses to SRIF and hGRF, there are at least two subpopulations of somatotrophs.

Genetics of Circadian Clocks

AbstractThe isolation of circadian clock mutants in Neurospora crassa and Drosophila melanogaster have identified numerous genes whose function is necessary for the normal operation of the circadian clock. In Neurospora many of these mutants map to a single locus called frq, whose properties suggest that its gene product is intimately involved in clock function. In Drosophila mutations at the per locus also suggest a significant role for the product of this gene in the insect clock mechanism. The per gene has been cloned and its gene product identified as a proteoglycan, most likely a membrane protein involved in affecting the ionic or electrical properties of cells in which it is located. Future progress in elucidating the mechanisms of circadian clocks are likely to come from continued analysis of clock mutants, both at the genetic and molecular levels.

Effects of intracellular pH and calcium activity on ion currents in internally perfused neurons of the snail Lymnaea stagnalis

The suction pipet method of intracellular dialysis and voltage clamp of cells has proven extremely useful in analysing the electrical properties of cells too small for the application of conventional microelectrode techniques and in larger cells for studying the effects of alterations in the internal ionic composition. Using neurons of the snail Lymnaea stagnalis, we have analysed several problems involved in the latter application of this technique and present several solutions to them. One major problem centers around the degree of control over the ionic composition of the cytoplasm achieved by altering the pipet solution. Using ion-sensitive microelectrodes during internal dialysis, we found that the efficiency of exchange between pipet and cytoplasm was much poorer for highly buffered ions such as H+ and Ca2+, than for K+, for example. Special precautions are described that can help this situation. The second problem involves the study of the effects of low internal pH on ion-channel properties. We summarize evidence for a specific voltage-dependent hydrogen ion channel, current through which becomes prominent at low internal pH. We analyse how the presence of this heretofore unrecognized current can seriously confuse the results of experiments designed to study the effects of low internal pH on other voltage-dependent currents.

Maturation of synapses and electrical properties of cells in the cochlear nuclei

Auditory nerve fibers carry impulses from the cochlea to the cochlear nuclei. There the temporal firing patterns of auditory nerve fibers are preserved by some cells and altered by others. The two factors which govern how firing patterns are shaped are (1) the intrinsic electrical properties of cells that determine the size and time course of voltage changes caused by synaptic currents and (2) the synaptic circuitry between cells. The electrical properties of cells were measured by recording the responses to current injected intracellularly into brain slice preparations. The synaptic responses to electrical shocks of the auditory nerve were used to determine the functional properties of synaptic connections. The three distinct types of electrical properties of cells that can be distinguished electrophysiologically in similar preparations of mature tissue, bushy and stellate cells in the ventral cochlear nucleus [(1984) J. Neurosci. 4, 1577–1588] and cells in the dorsal cochlear nucleus [Hirsch and Oertel (1987) (submitted); Oertel et al. (1987) In: Functions of the Auditory System, Editor: S. Hassler, J. Wiley and Sons (in press)] can be differentiated at least as early as 7 days after birth. Young cells, however, have higher input resistances and lower input capacitances than mature cells, and they cannot sustain high firing rates. Bushy and stellate cells in the ventral cochlear nucleus respond to electrical stimulation of the auditory nerve with both excitatory and inhibitory postsynaptic potentials as early as 4 days after birth. The synaptic potentials occur with longer and more variable latencies than in mature cells and synapses fatigue more easily, however. Cells of the dorsal cochlear nucleus also receive both excitatory and inhibitory synpatic inputs 4 days after birth, upon stimulation of the auditory nerve. No systematic changes were detected in these synaptic responses as a function of age but this may have been because the variability in the shape and timing of synaptic responses was large even in mature tissue.

Voltage-dependent ion channels in T-lymphocytes

The gigaohm seal ‘patch-clamp’ technique has recently enabled exploration of the electrical properties of cells of the immune system. In this paper we review progress made to date in cataloguing the ion channels present in the cell membranes of T-lymphocytes and present new data on the types of ion channels present in a number of human and murine T-cell-derived cell lines. The ion channels thus far described in these cells are strikingly similar to those found in nerve and muscle cells. Voltage-gated potassium channels resembling delayed rectifier potassium channels in excitable cells are present in most T-lymphocytes, T-lymphocyte-derived cell lines and macrophages. Sodium channels indistinguishable from those in excitable cells are present in a small fraction of T-cells and T-cell lines, and in some natural killer cells. Calcium channels have been reported in B-lymphocyte-derived cell lines, but have not been found in T-lymphocytes or in any T-cell-derived cell line. Potassium channels are required for activation of T-lymphocytes by mitogen, allogeneic cells, or by antigen, for lysis of target cells by natural killer cells, and may be involved in the triggering mechanism for activation of T-cells. The prevailing conception of early events in T-lymphocyte activation, the ‘calcium hypothesis’, involves an elevation of cytoplasmic free calcium levels as the proposed ‘second messenger’ in activation, giving rise to a cascade of subsequent events resulting eventually in cell division. A major focus of this paper is to evaluate specific mechanisms which have been proposed to account for experimental evidence, both in the literature and also presented here, pertaining to the calcium hypothesis. One such mechanism involves calcium channels, which have been postulated to account for the early calcium influx in activated T-lymphocytes. Since calcium channels have not been detected in T-cells, we explore the possibility that existing data can be accounted for without calcium channels. In particular, we show that many of the effects of ‘calcium channel antagonists’ such as verapamil, nifedipine, diltiazem and some polyvalent cations, can be accounted for by their blocking of voltage-gated potassium channels.

Electrical properties of normal and transformed mammalian cells

The transmembrane potential difference, Em, and DC membrane resistance were measured in 3T3 and polyoma virus-transformed 3T3 cells. Em was a function of cell density and was -12 and -25 mV for the normal and transformed cells, respectively. The external concentrations of K+, Na+, and Cl were varied in order to study the nature of the differences between the two cell types. The relative permeability of ions was calculated to be: PNa/PK, 1.0; PCl/PK, 1.88; PNa/PCl, 0.53 for 3T3 cells, and 0.27, 1.75, and 0.15 for the transformed cells. In contrast to the normal cells, PNa/PK varied as a function of the external K+ concentration for the transformed cells. It was emphasized that the manipulation of variables directly affecting the electrical properties of cells also involves the indirect manipulation of a network of interconnected physiological determinants.