scholarly journals Propagated spikes and secretion in a coelenterate glandular epithelium.

1976 ◽  
Vol 68 (3) ◽  
pp. 313-325 ◽  
Author(s):  
G O Mackie
Keyword(s):  
Action Potentials ◽  
Amorphous Material ◽  
Indirect Evidence ◽  
Resting Potential ◽  
Secretory Process ◽  
Outer Cell ◽  
Radial Canal ◽  
Calcium Dependent ◽  
Rete Mirabile ◽  
Rough Er

The rete mirabile of Hippopodius (Cl. Hydrozoa, O. Siphonophora) is a sheet of giant endoderm cells penetrated by branches of the ventral radial canal. The cells appear to be highly polyploid. The rough ER is very richly developed and expanded ER cisternae containing amorphous material (presumably synthesized protein) are observed near the outer cell surface. The cells are electrically coupled, and are connected by gap junctions. The rete is electrically excitable and cell to cell conduction of action potentials at 10 cm/s is observed. The action potentials are all-or-none, positive-going events, showing amplitudes of about 70 mV and arising from a 44 mV resting potential. Slowly developing and decaying secondary depolarizations, capable of summing to the 20 mV level, are also observed. After passage of a train of impulses, the rete cells swell and secretion drops appear at the surface, these changes becoming apparent within a few seconds. In 15 mM Mn2+ the response fails to occur, and secondary depolarizations ("secretion potentials") are not seen. Spike propagation is not affected. In Na+-free solutions the spikes are reduced and propagation eventually fails. It is suggested that the spikes are sodium-dependent events which trigger a calcium-dependent secretory process. The composition and biological activity of the secretion are uncertain, but indirect evidence suggests a possible defensive or repellant role for the response.

Effects of Octopamine on Calcium Action Potentials in Insect Oocytes

1989 ◽  
Vol 142 (1) ◽  
pp. 115-124
Author(s):  
M. J. O'DONNELL ◽  
B. SINGH
Keyword(s):  
Action Potentials ◽  
Rank Order ◽  
Potassium Conductance ◽  
Membrane Resistance ◽  
Threshold Concentration ◽  
Resting Potential ◽  
Calcium Dependent ◽  
Octopamine Receptors ◽  
Voltage Dependent ◽  
Maximum Rate Of Rise

Our experiments show that octopamine receptors are present on the developing follicles of an insect, Rhodnius prolixus. Application of D,L-octopamine decreased the duration and overshoot of calcium-dependent action potentials (APs), and increased the intrafollicular concentration of cyclic AMP. The threshold concentration of D,L-octopamine for the reduction in electrical excitability was between 1 and 5×10−7moll−1, and maximal effects of a 40–50% reduction in AP overshoot and duration were apparent at 10−4moll−1. At concentrations above 10−5moll−1, a small (<10%) hyperpolarization of the resting potential was also apparent. Effects of D,L-octopamine on oocyte excitability were independent of these small shifts in resting potential. Current injection experiments, in which calcium entry was blocked by cobalt, demonstrated that D,L-octopamine reduced membrane resistance at both hyperpolarizing and depolarizing potentials. Octopamine did not affect the maximum rate of rise of the AP, dV/dtmax, which is an indicator of inward calcium current. It is suggested that octopamine may mediate its effects on excitability through an increase in a voltage-dependent potassium conductance. Application of other phenolamines indicated a rank order of potency of D, Loctopamine > D,L-synephrine > tyramine. The α-adrenergic agonists clonidine, naphazoline and tolazoline were without significant effect at 10−5-10−3moll−1. Reduction of excitability by D,L-octopamine was effectively blocked by phentolamine and metoclopramide. Yohimbine and gramine were less effective as antagonists. Possible functions of octopamine receptors in insect follicles are discussed.

Na+-Dependent Neuritic Spikes Initiate Ca2+-Dependent Somatic Plateau Action Potentials in Insect Dorsal Paired Median Neurons

1998 ◽  
Vol 80 (5) ◽  
pp. 2718-2726 ◽  
Author(s):  
Corine Amat ◽  
Bruno Lapied ◽  
Andrew S. French ◽  
Bernard Hue
Keyword(s):  
Action Potentials ◽  
Periplaneta Americana ◽  
Resting Potential ◽  
Resting Membrane Potential ◽  
High Threshold ◽  
Calcium Dependent ◽  
Steady Current ◽  
Whole Cell Patch Clamp ◽  
Sodium Dependent ◽  
Monophasic Action Potentials

Amat, Corine, Bruno Lapied, Andrew S. French, and Bernard Hue. Na+-dependent neuritic spikes initiate Ca2+-dependent somatic plateau action potentials in insect dorsal paired median neurons J. Neurophysiol. 80: 2718–2726, 1998. The origin of plateau action potentials was studied in short-term cultures of dorsal paired median (DPM) neurons dissociated from the terminal abdominal ganglion of the cockroach, Periplaneta americana. Spontaneous plateau action potentials were recorded by intracellular microelectrodes in cell bodies that had neurite stumps. These action potentials featured a fast initial depolarization followed by a plateau. However, only fast spikes of short duration were observed when the cell was hyperpolarized from the resting membrane potential. These two different components of the action potentials could be separated by applying depolarizing current pulses from a hyperpolarized holding potential. Application of 200 nM tetrodotoxin (TTX) abolished both fast and slow phases, but depolarization to the original resting potential by steady current injection triggered slow monophasic action potentials that could be blocked by 3 mM CoCl2. In contrast, DPM neurons without neurites were not spontaneously active. In these cells, calcium-dependent slow monophasic action potentials were only recorded immediately after impalement or with current pulse stimulation. Immunocytochemical observations showed that dorsal unpaired median (DUM) neuron cell bodies, which are known to exhibit spontaneous sodium-dependent action potentials, reacted with an antibody directed against a synthetic peptide corresponding to the SP19 segment of voltage-activated sodium channels. In contrast, the antibody did not stain DPM neuron cell bodies but gave intense, patchy staining only in the neurite. Whole cell patch-clamp experiments performed on isolated DPM neuron cell bodies without a neurite revealed the presence of an inward current that did not inactivate completly within the duration of the test pulse. This current was insensitive to both 100 nM TTX and sodium-free saline. It was defined as a high-voltage-activated calcium current according to its high threshold of activation (−30 mV) and its sensitivity to 1 mM CdCl2 and 100 nM ω-conotoxin GVIA. Our findings demonstrate that spontaneous sodium-dependent spikes arising from the neurite are required to initiate slow somatic calcium-dependent action potentials in DPM neurons.

scholarly journals Electrophysiological engineering of heart-derived cells with calcium-dependent potassium channels improves cell therapy efficacy for cardioprotection

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Patrick Vigneault ◽  
Sandrine Parent ◽  
Pushpinder Kanda ◽  
Connor Michie ◽  
Darryl R. Davis ◽  
...  
Keyword(s):  
Cell Therapy ◽  
Therapeutic Potential ◽  
Resting Potential ◽  
Intramyocardial Injection ◽  
Membrane Hyperpolarization ◽  
Calcium Dependent ◽  
Cell Functions ◽  
Kca Channels ◽  
Therapy Effectiveness ◽  
Intracellular Ca

AbstractWe have shown that calcium-activated potassium (KCa)-channels regulate fundamental progenitor-cell functions, including proliferation, but their contribution to cell-therapy effectiveness is unknown. Here, we test the participation of KCa-channels in human heart explant-derived cell (EDC) physiology and therapeutic potential. TRAM34-sensitive KCa3.1-channels, encoded by the KCNN4 gene, are exclusively expressed in therapeutically bioactive EDC subfractions and maintain a strongly polarized resting potential; whereas therapeutically inert EDCs lack KCa3.1 channels and exhibit depolarized resting potentials. Somatic gene transfer of KCNN4 results in membrane hyperpolarization and increases intracellular [Ca2+], which boosts cell-proliferation and the production of pro-healing cytokines/nanoparticles. Intramyocardial injection of EDCs after KCNN4-gene overexpression markedly increases the salutary effects of EDCs on cardiac function, viable myocardium and peri-infarct neovascularization in a well-established murine model of ischemic cardiomyopathy. Thus, electrophysiological engineering provides a potentially valuable strategy to improve the therapeutic value of progenitor cells for cardioprotection and possibly other indications.

Properties of visceral primary afferent neurons in the nodose ganglion of the rabbit

1985 ◽  
Vol 54 (2) ◽  
pp. 245-260 ◽  
Author(s):  
C. E. Stansfeld ◽  
D. I. Wallis
Keyword(s):  
Action Potentials ◽  
Input Resistance ◽  
Nodose Ganglion ◽  
Time Dependent ◽  
Membrane Properties ◽  
Resting Potential ◽  
Inward Rectification ◽  
C Cells ◽  
Axonal Conduction ◽  
A Cells

The active and passive membrane properties of rabbit nodose ganglion cells and their responsiveness to depolarizing agents have been examined in vitro. Neurons with an axonal conduction velocity of less than 3 m/s were classified as C-cells and the remainder as A-cells. Mean axonal conduction velocities of A- and C-cells were 16.4 m/s and 0.99 m/s, respectively. A-cells had action potentials of brief duration (1.16 ms), high rate of rise (385 V/s), an overshoot of 23 mV, and relatively high spike following frequency (SFF). C-cells typically had action potentials with a "humped" configuration (duration 2.51 ms), lower rate of rise (255 V/s), an overshoot of 28.6 mV, an after potential of longer duration than A-cells, and relatively low SFF. Eight of 15 A-cells whose axons conducted at less than 10 m/s had action potentials of longer duration with a humped configuration; these were termed Ah-cells. They formed about 10% of cells whose axons conducted above 2.5 m/s. The soma action potential of A-cells was blocked by tetrodotoxin (TTX), but that of 6/11 C-cells was unaffected by TTX. Typically, A-cells showed strong delayed (outward) rectification on passage of depolarizing current through the soma membrane and time-dependent (inward) rectification on inward current passage. Input resistance was thus highly sensitive to membrane potential close to rest. In C-cells, delayed rectification was not marked, and slight time-dependent rectification occurred in only 3 of 25 cells; I/V curves were normally linear over the range: resting potential to 40 mV more negative. Data on Ah-cells were incomplete, but in our sample of eight cells time-dependent rectification was absent or mild. C-cells had a higher input resistance and a higher neuronal capacitance than A-cells. In a proportion of A-cells, RN was low at resting potential (5 M omega) but increased as the membrane was hyperpolarized by a few millivolts. A-cells were depolarized by GABA but were normally unaffected by 5-HT or DMPP. C-cells were depolarized by GABA in a similar manner to A-cells but also responded strongly to 5-HT; 53/66 gave a depolarizing response, and 3/66, a hyperpolarizing response. Of C-cells, 75% gave a depolarizing response to DMPP.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium-dependent potassium conductance in rat supraoptic nucleus neurosecretory neurons

1985 ◽  
Vol 54 (6) ◽  
pp. 1375-1382 ◽  
Author(s):  
C. W. Bourque ◽  
J. C. Randle ◽  
L. P. Renaud
Keyword(s):  
Time Constant ◽  
Action Potentials ◽  
Supraoptic Nucleus ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Input Resistance ◽  
Mean Amplitude ◽  
Progressive Increase ◽  
Calcium Dependent ◽  
Neurosecretory Neurons

Intracellular recordings of rat supraoptic nucleus neurons were obtained from perfused hypothalamic explants. Individual action potentials were followed by hyperpolarizing afterpotentials (HAPs) having a mean amplitude of -7.4 +/- 0.8 mV (SD). The decay of the HAP was approximated by a single exponential function having a mean time constant of 17.5 +/- 6.1 ms. This considerably exceeded the cell time constant of the same neurons (9.5 +/- 0.8 ms), thus indicating that the ionic conductance underlying the HAP persisted briefly after each spike. The HAP had a reversal potential of -85 mV and was unaffected by intracellular Cl- ionophoresis of during exposure to elevated extracellular concentrations of Mg2+. In contrast, the peak amplitude of the HAP was proportional to the extracellular Ca2+ concentration and could be reversibly eliminated by replacing Ca2+ with Co2+, Mn2+, or EGTA in the perfusion fluid. During depolarizing current pulses, evoked action potential trains demonstrated a progressive increase in interspike intervals associated with a potentiation of successive HAPs. This spike frequency adaptation was reversibly abolished by replacing Ca2+ with Co2+, Mn2+, or EGTA. Bursts of action potentials were followed by a more prolonged afterhyperpolarization (AHP) whose magnitude was proportional to the number of impulses elicited (greater than 20 Hz) during a burst. Current injection revealed that the AHP was associated with a 20-60% decrease in input resistance and showed little voltage dependence in the range of -70 to -120 mV. The reversal potential of the AHP shifted with the extracellular concentration of K+ [( K+]o) with a mean slope of -50 mV/log[K+]o.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiology of neurosecretory cells from the pituitary intermediate lobe

1988 ◽  
Vol 139 (1) ◽  
pp. 317-328
Author(s):  
R. N. McBurney ◽  
S. J. Kehl
Keyword(s):  
Cell Cultures ◽  
Calcium Ion ◽  
Action Potentials ◽  
Neurosecretory Cells ◽  
Secretory Process ◽  
High Threshold ◽  
Pars Intermedia ◽  
Low Threshold ◽  
Stimulus Secretion Coupling ◽  
Ca2 Channels

One of the goals in studying the electrical properties of neurosecretory cells is to relate their electrical activity to the process of secretion. A central question in these studies concerns the role of transmembrane calcium ion flux in the initiation of the secretory event. With regard to the secretory process in pituitary cells, several research groups have addressed this question in vitro using mixed primary anterior pituitary cell cultures or clonal cell lines derived from pituitary tumours. Other workers, including ourselves, have used homogeneous cell cultures derived from the pituitary intermediate lobes of rats to examine the characteristics of voltage-dependent conductances, the contribution of these conductances to action potentials and their role in stimulus-secretion coupling. Pars intermedia (PI) cells often fire spontaneous action potentials whose frequency can be modified by the injection of sustained currents through the recording electrode. In quiescent cells action potentials can also be evoked by the injection of depolarizing current stimuli. At around 20 degrees C these action potentials have a duration of about 5 ms. Although most of the inward current during action potentials is carried by sodium ions, a calcium ion component can be demonstrated under abnormal conditions. Voltage-clamp experiments have revealed that the membrane of these cells contains high-threshold, L-type, Ca2+ channels and low-threshold Ca2+ channels. Since hormone release from PI cells appears not to be dependent on action potential activity but does depend on external calcium ions, it is not clear what role these Ca2+ channels play in stimulus-secretion coupling in cells of the pituitary pars intermedia. One possibility is that the low-threshold Ca2+ channels are more important to the secretory process than the high-threshold channels.

Electrophysiology of the Giant Nerve Cell Bodies of Limnaea Stagnalis (L.) (Gastropoda: Pulmonata)

1974 ◽  
Vol 60 (3) ◽  
pp. 653-671
Author(s):  
D. B. SATTELLE
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Cell Types ◽  
Resting Potential ◽  
Constant Field ◽  
Bathing Medium ◽  
Mean Values ◽  
Relative Contribution ◽  
External Potassium ◽  
Limnaea Stagnalis

1. A mean resting potential of -53.3 (S.D. ±2.7) mV has been obtained for 23 neurones of the parietal and visceral ganglia of Limnaea stagnalis (L.). Changes in the resting potential of between 28 and 43 mV accompany tenfold changes in [K+0]. A modified constant-field equation accounts for the behaviour of most cells over the range of external potassium concentrations from 0-5 to 10.o mM/1. Mean values have been estimated for [K+1, 56.2 (S.D.± 9-0) mM/1 and PNa/PK, 0-117 (S.D.±0-028). 2. Investigations on the ionic basis of action potential generation have revealed two cell types which can be distinguished according to the behaviour of their action potentials in sodium-free Ringer. Sodium-sensitive cells are unable to support action potentials for more than 8-10 min in the absence of sodium. Sodium slopes of between 29 and 37 mV per decade change in [Na+0] have been found for these cells. Tetrodotoxin (5 x 10-5 M) usually blocks action potentials in these neurones. Calcium-free inger produces a marked reduction in the overshoot potential and calcium slopes of about 18 mV per decade change in [Ca2+o] are found. Manganous chloride only partially reduces the action potential overshoot in these cells at concentrations of 10 mM/l. 3. Sodium-insensitive neurones maintain action potentials in the absence of external sodium. Stimulation only slightly reduces the amplitude of the action potential under these conditions and such cells are readily accessible to potassium ions in the bathing medium. A calcium-slope of 29 mV per decade change in [Ca2+o] has been observed in these cells in the absence of external sodium. 4. It is concluded that both sodium and calcium ions can be involved in the generation of the action potential in neurones of Limnaea stagnate, their relative contribution varying in different cells.

Membrane resistance increases when automaticity develops in explanted rat heart cells

1990 ◽  
Vol 258 (1) ◽  
pp. H145-H152 ◽  
Author(s):  
O. F. Schanne ◽  
M. Lefloch ◽  
B. Fermini ◽  
E. Ruiz-Petrich
Keyword(s):  
Spontaneous Activity ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Heart Cells ◽  
Membrane Capacity ◽  
Rat Heart Cells ◽  
Specific Membrane

We compared the passive electrical properties of isolated ventricular myocytes (resting potential -65 mV, fast action potentials, and no spontaneous activity) with those of 2- to 7-day-old cultured ventricle cells from neonatal rats (resting potential -50 mV, slow action potentials, and presence of spontaneous activity). In myocytes the specific membrane capacity was 0.99 microF/cm2, and the specific membrane resistance increased from 2.46 k omega.cm2 at -65 mV to 7.30 k omega.cm2 at -30 mV. In clusters, the current-voltage relationships measured under current-clamp conditions showed anomalous rectification and the input resistance decreased from 1.05 to 0.48 M omega when external K+ concentration was increased from 6 to 100 mM. Using the model of a finite disk we determined the specific membrane resistance (12.9 k omega.cm2), the effective membrane capacity (17.8 microF/cm2), and the lumped resistivity of the disk interior (1,964 omega.cm). We conclude that 1) the voltage dependence of the specific membrane resistance cannot completely explain the membrane resistance increase that accompanies the appearance of spontaneous activity; 2) a decrease of the inwardly rectifying conductance (gk1) is mainly responsible for the increase in the specific membrane resistance and depolarization; and 3) approximately 41% of the inward-rectifying channels are electrically silent when spontaneous activity develops in explanted ventricle cells.

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