Cellular physiology of the neonatal rat cerebral cortex: Intrinsic membrane properties, sodium and calcium currents (original) (raw)
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Calcium currents in cultured rat cortical neurons
Brain Research, 1989
Rat neocortical neurons grown in dissociated cell culture for 4-12 weeks were studied with whole-cell patch-clamp techniques in order to characterize the calcium currents present in these cells. When voltage-dependent Na and K currents were inhibited, depolarizations from negative holding potentials induced inward currents which had 3 components: a low threshold activated, small, relatively persistent component, which was completely inactivated at holding potentials more positive then-60 mV; a higher threshold, relatively persistent component (which was not inactivated at VH =-50 mV); and a higher threshold, larger, transient component. All 3 components were reduced by removal of Ca, and blocked by Cd and Ni at appropriate concentrations. The components were differentially affected by low concentrations of Ni (500/~M), nifedipine (500/~M) and Ba (1.8 mM). Only the first two components were present in very young neurons.
A low voltage-activated calcium conductance in embryonic chick sensory neurons
Biophysical Journal, 1984
Isolated Ca currents in cultured dorsal root ganglion (DRG) cells were studied using the patch clamp technique. The currents persisted in the presence of 30 ,uM tetrodotoxin (TTX) or when external Na was replaced by choline. They were fully blocked by millimolar additions of Cd2" and Ni2" to the bath. Two components of an inward-going Ca current were observed. In 5 mM external Ca, a current of small amplitude, turned on already during steps changes to-60 mV membrane potential, leveled off at-30 mV to a value of-0.2 nA. A second, larger current component, which resembled the previously described Ca current in other cells, appeared at more positive voltages (-20 to-10 mV) and had a maximum-0 mV. The current component activated at the more negative membrane potentials showed the stronger dependence on external Ca. The presence of a timeand a voltage-dependent activation was indicated by the current's sigmoidal rise, which became faster with increased depolarization. Its tail currents were generally slower than those associated with the Ca currents of larger amplitude. From-60 mV holding potential, the maximum obtainable amplitude of the low depolarization-activated current was only one-tenth of that achieved from a holding potential of-90 mV. Voltage-dependent inactivation of this current component was fast compared with that of the other component. The properties of this low voltage-activated and fully inactivating Ca current suggest it is the same as the inward current that has been postulated in several central neurons (Llinas, R., and Y. Yarom, 1981, J. Physiol. (Lond.), 315:569-584), which produce depolarizing potential waves and burst-firing only when membrane hyperpolarization precedes.
Developmental regulation of T-, N- and L-type calcium currents in mouse embryonic sensory neurones
European Journal of Neuroscience, 1998
We investigated the development of a low (T-type) and two high voltage-activated (N-and L-type) calcium channel currents in large diameter dorsal root ganglion neurones acutely isolated from embryonic mice using the whole-cell patch-clamp technique. The low and high voltage-activated barium currents (LVA and HVA) were identified by their distinct threshold of activation and their sensitivity to pharmacological agents, dihydropyridines and ω-conotoxin-GVIA, at embryonic day 13 (E13), E15 and E17-18, respectively, before, during and after synaptogenesis. The amplitude and density of LVA currents, measured during a -40 mV pulse from a holding potential of -100 mV, increased significantly between E13 and E15, and remained constant between E15 and E17-18. The density of global HVA current, elicited by 0 mV pulse, increased between E13 and E15/E17-18.
Brain Research, 1991
Current-clamp studies have shown that voltage-dependent Ca currents are present in rat neostriatal neurons. Although these studies have provided evidence for the presence of high-voltage activated Ca channels, it has been unclear whether low-voltage activated channels are also present. Using the whole-cell variant of the patch-clamp technique, we have studied isolated Ca currents in an attempt to answer this question. We have found that both high-and low-voltage activated calcium currents are expressed by neostriatal neurons cultured from embryonic rat brain. These currents are similar in voltage-dependence and pharmacology to those found in other brain neurons.
Development of calcium current subtypes in isolated rat hippocampal pyramidal cells
The Journal of physiology, 1991
1. Patch-clamp techniques were used to record from acutely dissociated rat hippocampal pyramidal cells of different postnatal ages to study the development, kinetics of activation and inactivation, and pharmacology of various components of whole-cell calcium current. 2. In both adult and immature pyramidal cells, the threshold of activation for Ca2+ current from the holding potential of -50 mV was about -35 mV. The current was non-inactivating near threshold, and slowly inactivating with stronger depolarizations. 3. In adult pyramidal cells, hyperpolarizing pre-pulses (-85 mV, 3 s) increased the peak amplitude of current, but had little effect on the amplitude of sustained current or on the threshold. In immature cells, hyperpolarizing pre-pulses (-85 mV, 3 s) revealed an additional component of Ca2+ current that had a threshold for activation around -60 mV, and inactivated rapidly and completely at potentials between -60 and -35 mV. This low-threshold Ca2+ current was found in all ...
Stem Cells and Development, 2013
The central role of calcium influx and electrical activity in embryonic development raises important questions about the role and regulation of voltage-dependent calcium influx. Using cultured neural progenitor cell (NPC) preparations, we recorded barium currents through voltage-activated channels using the whole-cell configuration of the patch-clamp technique and monitored intracellular free calcium concentrations with Fura-2 digital imaging. We found that NPCs as well as expressing high-voltage-activated (HVA) calcium channels express functional low-threshold voltage-dependent calcium channels in the very early stages of differentiation (5 h to 1 day). The size of the currents recorded at -50 versus -20 mV after 1 day in differentiation was dependent on the nature of the charge carrier. Peak currents measured at -20 mV in the presence 10 mM Ca 2 + instead of 10 mM Ba 2 + had a tendency to be smaller, whereas the nature of the divalent species did not influence the amplitude measured at -50 mV. The T-type channel blockers mibefradil and NNC 55-0396 significantly reduced the calcium responses elicited by depolarizing with extracellular potassium, while the overall effect of the HVA calcium channel blockers was small at differentiation day 1. At differentiation day 20, the calcium responses were effectively blocked by nifedipine. Time-lapse imaging of differentiating neurospheres cultured in the presence of low-voltage-activated (LVA) blockers showed a significant decrease in the number of active migrating neuron-like cells and neurite extensions. Together, these data provide evidence that LVA calcium channels are involved in the physiology of differentiating and migrating NPCs.
Journal of Neurophysiology, 1997
Kammermeier, Paul J. and Stephen W. Jones. High-voltage-activated calcium currents in neurons acutely isolated from the ventrobasal nucleus of the rat thalamus. J. Neurophysiol. 77: 465–475, 1997. We studied the high-voltage-activated (HVA) calcium currents in cells isolated from the ventrobasal nucleus of the rat thalamus with the use of the whole cell patch-clamp technique. Low-voltage-activated current was inactivated by the use of long voltage steps or 100-ms prepulses to −20 mV. We used channel blocking agents to characterize the currents that make up the HVA current. The dihydropyridine (DHP) antagonist nimodipine (5 μM) reversibly blocked 33 ± 1% (mean ± SE), and ω-conotoxin GVIA (1 μM) irreversibly blocked 25 ± 5%. The current resistant to DHPs and ω-conotoxin GVIA was inhibited almost completely by ω-conotoxin MVIIC (90 ± 5% at 3–5 μM) and was partially inhibited by ω-agatoxin IVA (54 ± 4% block at 1 μM). We conclude that there are at least four main HVA currents in thalami...
The Journal of Physiology, 1999
Voltage-activated calcium currents (VACCs) have a primary role in regulating membrane electrophysiological behaviour, intercellular communication and other non-membranal cell functions in neurones (Llin as, 1988; Berridge, 1998). VACCs can influence neuronal electroresponsiveness both directly, by sustaining inward currents that promote depolarizing responses, and indirectly, by recruiting calcium-dependent currents. The kinetic properties and the voltage range of activation of the underlying calcium conductances are key elements in determining the specific contribution of the various VACC types in neuronal functions. For instance, a calcium current activated at more negative voltage levels than another one of similar size will have a stronger depolarizing effect on neuronal membrane: at relatively negative voltage levels, indeed, a higher membrane input resistance and a lesser weight of repolarizing potassium currents due to a smaller driving force for potassium ions are to be expected. The characterization of the calcium currents expressed by a given neuronal type can therefore be relevant to the understanding of its specific functional behaviour.