Disposition of TF-PEG-Liposome-BSH in tumor-bearing mice

BNCT requires high concentration and selective delivery of (10)B to the tumor cell. To improve the drug delivery in BNCT, we conducted a study by devising TPLB. We administrated three types of boron delivery systems: BSH, PLB and TPLB, to Oral SCC bearing mice. Results confirmed that (10)B concentration is higher in the TPLB group than in the BSH group and that TPLB is significantly effective as boron delivery system.

Catecholamine secretion from rat foetal adrenal chromaffin cells and hypoxia sensitivity

The adrenal medulla chromaffin cells (AMCs) secrete catecholamines in response to various types of stress. We examined the hypoxia-sensitivity of catecholamine secretion by rat foetal chromaffin cells in which the innervation by the splanchnic nerve is not established. The experiments were performed in primary cultured cells from two different ages of foetuses (F15 and F19). Membrane potential of AMCs was monitored with the patch clamp technique, and the catecholamine secretion was detected by amperometry. We found that: (1) AMCs from F19 foetuses showed hypoxia-induced catecholamine release. (2) This hypoxia-induced secretion is produced by membrane depolarization generated by an inhibition of Ca(2+)-activated K(+) current [I (K(Ca))] current. (3) Chromaffin precursor cells from F15 foetuses secrete catecholamine. The quantal release is calcium-dependent, but the size of the quantum is reduced. (4) In the precursor cells, a hypoxia-induced membrane hyperpolarization is originated by an ATP-sensitive K(+) current [I (K(ATP))] activation. (5) During the prenatal period, at F15, the percentage of the total outward current for I (K(ATP)) and I (K(Ca)) was 50 and 29.5%, respectively, whereas at F19, I (K(ATP)) is reduced to 14%, and I (K(Ca)) became 64% of the total current. We conclude that before birth, the age-dependent hypoxia response of chromaffin cells is modulated by the functional activity of K(ATP) and K(Ca) channels.

A new omega-conotoxin that targets N-type voltage-sensitive calcium channels with unusual specificity

A new specific voltage-sensitive calcium channel (VSCC) blocker has been isolated from the venom of the fish-hunting cone snail Conus consors. This peptide, named omega-Ctx CNVIIA, consists of 27 amino acid residues folded by 3 disulfide bridges. Interestingly, loop 4, which is supposed to be crucial for selectivity, shows an unusual sequence (SSSKGR). The synthesis of the linear peptide was performed using the Fmoc strategy, and the correct folding was achieved in the presence of guanidinium chloride, potassium buffer, and reduced/oxidized glutathione at 4 degrees C for 3 days. Both synthetic and native toxin caused an intense shaking activity, characteristic of omega-conotoxins targeting N-type VSCC when injected intracerebroventricularly to mice. Binding studies on rat brain synaptosomes revealed that the radioiodinated omega-Ctx CNVIIA specifically and reversibly binds to high-affinity sites with a K(d) of 36.3 pM. Its binding is competitive with omega-Ctx MVIIA at low concentration (K(i) = 2 pM). Moreover, omega-Ctx CNVIIA exhibits a clear selectivity for N-type VSCCs versus P/Q-type VSCCs targeted respectively by radioiodinated omega-Ctx GVIA and omega-Ctx MVIIC. Although omega-Ctx CNVIIA clearly blocked N-type Ca(2+) current in chromaffin cells, this toxin did not inhibit acetylcholine release evoked by nerve stimuli at the frog neuromuscular junction, in marked contrast to omega-Ctx GVIA. omega-Ctx CNVIIA thus represents a new selective tool for blocking N-type VSCC that displays a unique pharmacological profile and highlights the diversity of voltage-sensitive Ca(2+) channels in the animal kingdom.

Low threshold T-type calcium current in rat embryonic chromaffin cells

1. The gating kinetics and functions of low threshold T-type current in cultured chromaffin cells from rats of 19-20 days gestation (E19-E20) were studied using the patch clamp technique. Exocytosis induced by calcium currents was monitored by the measurement of membrane capacitance and amperometry with a carbon fibre sensor. 2. In cells cultured for 1-4 days, the embryonic chromaffin cells were immunohistochemically identified by using polyclonal antibodies against dopamine beta-hydroxylase (DBH) and syntaxin. The immuno-positive cells could be separated into three types, based on the recorded calcium current properties. Type I cells showed exclusively large low threshold T-type current, Type II cells showed only high voltage activated (HVA) calcium channel current and Type III cells showed both T-type and HVA currents. These cells represented 44 %, 46 % and 10 % of the total, respectively. 3. T-type current recorded in Type I cells became detectable at -50 mV, reached its maximum amplitude of 6.8 +/- 1.2 pA pF(-1) (n = 5) at -10 mV and reversed around +50 mV. The current was characterized by criss-crossing kinetics within the -50 to -30 mV voltage range and a slow deactivation (deactivation time constant, tau(d) = 2 ms at -80 mV). The channel closing and inactivation process included both voltage-dependent and voltage-independent steps. The antihypertensive drug mibefradil (200 nM) reduced the current amplitude to about 65 % of control values. Ni(2+) also blocked the current in a dose-dependent manner with an IC(50) of 25 microM. 4. T-type current in Type I cells did not induce exocytosis, while catecholamine secretion by exocytosis could be induced by HVA calcium current in both Type II and Type III cells. The failure to induce exocytosis by T-type current in Type I cells was not due to insufficient Ca(2+) influx through the T-type calcium channel. 5. We suggest that T-type current is expressed in developing immature chromaffin cells. The T-type current is replaced progressively by HVA calcium current during pre- and post-natal development accompanying the functional maturation of the exocytosis mechanism.

Development of multiple calcium channel types in cultured mouse hippocampal neurons

The development of multiple calcium channel activities was studied in mouse hippocampal neurons in culture, using the patch-clamp technique. A depolarizing pulse (40-50 ms duration) from the holding potential of -80 mV to levels more depolarized than -40 mV produced a low threshold T-type current. The T-type current was observed in 52% of four days in vitro neurons. The number of neurons which expressed T-type current decreased with age of culture, so that the current was detected in only 18% of neurons after 16 days in vitro. The T-type current densities varied between 1.9 pA/pF and 3.29 pA/pF in the mean values during the period studied (4-16 days in vitro). A depolarizing pulse from -80 mV to levels more depolarized than -35 mV evoked a high threshold calcium channel current. The high threshold current density increased in the mean values from 3.9 pA/pF in four days in vitro neurons to 28 pA/pF in 16 days in vitro neurons. We have then examined the effect of nifedipine, omega-Agatoxin IVA and omega-conotoxin GVIA on the high threshold current. Nifedipine (1-5 microM) sensitive current density stayed in the range of 1.9-2.1 pA/pF during 4-16 days in vitro, while omega-Agatoxin IVA (200 nM) sensitive current density increased in the mean values from 1.54 pA/pF in four days in vitro neurons to 21.5 pA/pF in 16 days in vitro neurons. The omega-conotoxin GVIA sensitive N-type channel current was maximum at eight days in vitro (5.44 pA/pF) and it reduced progressively to reach almost half (2.46 pA/pF) in 16 days in vitro neurons. These results showed that diverse subtypes of calcium channels change in density during the early period of culture. We suggest that the temporal expression of each type of channel may be linked to the development of neural activities.

Calcium signals in cell lines derived from the cerebral cortex of normal and trisomy 16 mice

We established two immortalized cell lines from cerebral cortex of normal (CNh) and trisomy 16 (CTb) mouse fetuses, an animal model of human trisomy 21. Those cells loaded with the fluorescent Ca2+ dyes, Indo-1 and Fluo-3, exhibited increments of intracellular Ca2+ ([Ca2+]i) in response to external glutamate, NMDA, AMPA and kainate. CTb cells exhibited higher basal Ca2+ concentrations and had higher amplitude and slower time-dependent kinetics in the decay than CNh cells, suggesting an impaired Ca2+ buffering capacity in the trisomy 16-derived cell line. Nicotine also induced increments of [Ca2+]i. The CTb cell line could represent a model for studying cellular alterations related to Down syndrome.

The action of diltiazem and gallopamil (D600) on calcium channel current and charge movement in mouse Purkinje neurons

The dihydropyridines (DHP) receptor forms a high threshold L-type calcium channel in various excitable cells. In skeletal and cardiac muscle cells, a DHP receptor antagonist blocks not only the voltage-gated calcium current but also immobilizes the charge movement linked to the receptor. The DHP receptor is also present in cerebellar Purkinje neurons. Previously, we showed that nifedipine immobilizes a part of the charge movement but has no effect on the calcium channel current recorded in freshly dissociated mice Purkinje neurons. We report here the effect of other families of DHP receptor antagonists, benzothiazepines and phenylalkylamines, on the physiological properties of this receptor in mouse Purkinje neurons.

Effect of lipophilic ions on the intramembrane charge movement and intracellular Ca2+ release in fetal mouse skeletal muscle cells

The effects of lipophilic ions on the intramembrane charge movement and intracellular calcium transient were studied using freshly dissociated skeletal muscle cells from mice fetuses. The lipophilic cations Rhodamine 6G and tetraphenylphosphonium (TPP) immobilized part of the intramembrane charge movement in a dose-dependent manner, and inhibited both calcium transient and contraction evoked by membrane depolarization. In contrast, the lipophilic anion 1-anilinonaphthalene-8-sulfonic acid (ANS) had no effect on intramembrane charge movement. We suggest that the lipophilic cations block the voltage-sensing mechanism for the excitation-contraction (E-C) coupling mechanism.

Effect of SR33805 on barium current and asymmetric intramembrane charge movement in freshly dissociated mouse cerebellar Purkinje neurons

SR33805 is a novel calcium channel blocker that binds selectively and with high affinity to the alpha 1 subunit of the L-type calcium channel. The binding site for SR33805 is distinct from other classical calcium channel blockers although they interact allosterically. The block by SR33805 of the neuronal L-type calcium current has been reported [Romey, G. and Lazdunski, M., J. Pharmacol. Exp. Ther., 271 (1994) 1348-1352.]. In Purkinje neurons, the L-type calcium current is nearly absent. Nevertheless, we have shown the presence of intramembrane charge movement related to the dihydropyridines (DHP) receptor in these neurons. We show here that SR33805 has no effect on barium currents recorded in Purkinje cells but is a very potent blocker of intramembrane charge movement. It reduces charge movement to 48% of control with an IC50 of 0.5 nM.

cAMP-dependent modulation of L-type calcium currents in mouse diaphragmatic cells

The regulation of calcium channels by cAMP-dependent phosphorylation was investigated in the diaphragm muscle. Experiments were performed on dissociated costal diaphragmatic cells from 16- to 17-day-old fetal mice. The ionic current through calcium channels was measured using the whole cell clamp technique with barium as the charge carrier. A depolarizing pulse delivered from a holding potential of -80 mV elicited a low-threshold dihydropyridine (DHP)-insensitive T-type current and a high-threshold DHP-sensitive L-type current. Agents that either increase intracellular cAMP levels (forskolin, 10(-4) M, and dibutyryladenosine 3'-5' cyclic monophosphate, 10(-4) M) or inhibit cAMP degradation (theophylline, 10(-4) M) produced relative increases in L-type current amplitude of 24.4 +/- 13.8%, 13.4 +/- 4.6%, and 15.9 +/- 2.8% (p < 0.05), respectively. Current intensity increased after application of the beta-adrenergic agonist isoproterenol (10(-5) M, 16.5 +/- 3.6%, P < 0.005). None of these agents affected the T-type current. These results suggest that L-type calcium channel activities of the diaphragm muscle are regulated by cAMP-dependent phosphorylation.

Nifedipine-sensitive intramembrane charge movement in Purkinje cells from mouse cerebellum

1. The intramembrane charge movement was recorded in freshly dissociated Purkinje cells from 14- to 18-day-old mouse cerebellum using the whole-cell voltage clamp technique. 2. After pharmacological elimination of all ionic currents, a depolarizing pulse from a holding potential of -80 mV revealed a transient capacitive outward current at the onset and a transient inward current at the end of the pulse. The amount of charge transferred at the onset (Qon) was equivalent to that moved at the end of the pulse (Qoff). The decay time course of Qon can be fitted by a single exponential curve with a maximum time constant of 1.89 +/- 0.35 ms at 20 mV (n = 11). 3. The charge movement had an S-shaped dependence on test membrane potential, according to a two-state Boltzmann function. The maximum amount (Qmax) of Qon that could be moved was 17.46 +/- 0.83 nC muF-1; the membrane potential at which half the charge movement occurred (V) was 13.48 +/- 2.20 mV and the slope factor (k) was 16.83 +/- 0.84 mV (n = 27). 4. Phenylglyoxal (2 mM), an arginine-specific modifying reagent, reduced Qmax to 60% of control after 20 min treatment. 5. The charge movement was partially immobilized by nifedipine in a dose-dependent manner with an IC50 of 70 nM. The fraction of the nifedipine-sensitive component was 39% of the total charge movement. The potential dependence of the nifedipine-sensitive charge movement could be expressed by a Boltzmann function with values of 7.00 +/- 0.53 nC muF-1 for Qmax, 31.44 +/- 4.23 mV for V and 21.53 +/- 3.18 mV for k (n = 8). 6. The P-type calcium channel specific inhibitor, omega-Aga IVA (250 nM), had no effect on intramembrane charge movement. 7. The above results show that part of the intramembrane charge movement in Purkinje cells may be related to a conformational change of DHP receptors upon membrane depolarization.

Ca2+ entry through acetylcholine receptor channel in dysgenic myotubes

Skeletal muscles of mutant mice with "muscular dysgenesis" are characterized by excitation-contraction uncoupling resulting from the absence of dihydropyridine receptors. However contraction of the dysgenic myotubes can be evoked by afferent nerve stimulation or by ionophoretic application of acetylcholine (ACh) on the muscle. These contractions are elicited by Ca2+ entry through the ionic channel of the ACh receptor at multiple synaptic contacts. In the present paper, the calcium entry through ACh receptors was compared in cultured normal and dysgenic myotubes. At elevated external calcium concentration (110 mM), the elementary slope conductance of the ACh-activated ionic channel of dysgenic myotubes did not differ from that found in normal myotubes. We conclude that dysgenic muscle contraction induced by nerve stimulation does not result from an abnormal Ca2+ entry across ACh receptors. We discuss the possible involvement of sustained high threshold calcium current (Idys) and of the calcium induced calcium release mechanism in the contractile response related to synaptic activity of dysgenic myotubes.

Asymmetric intramembrane charge movement in mouse hippocampal pyramidal cells

Intramembrane charge movement was recorded from freshly dissociated hippocampal pyramidal cells from mice using the whole cell clamp technique. Once the ionic currents were suppressed, a depolarizing pulse from a holding potential of -80 mV elicited a capacitive transient outward current at onset and a capacitive inward current at offset of the pulse. The amount of charge displaced at the onset of the pulse (Qon) was equivalent to the charge moved at repolarization (Qoff). The relationship between the amount of charge moved and pulse potential could be expressed by a simple two states Boltzmann equation: Q = Qmax/(1 + exp[-(V-V1/2)/k]), where Qmax is the maximum charge, V1/2 the membrane potential at which Q is half of Qmax and k is a slope factor. On average, Qmax was 10.90 +/- 0.62 nC/microF, V1/2 was 1.70 +/- 2.90 mV, and k was 18.80 +/- 1.20 mV (n = 16). Phenylglyoxal (10 mM), an arginine modifying reagent, reduced the maximum amount of charge movement to 14% of control. The inhibitory effect of phenylglyoxal was time dependent and the decline time course of maximum amount of charge movement could be fitted by a single exponential curve with a time constant of 5.79 min. The dihydropyridine (DHP) receptor antagonist, nifedipine, immobilized 54% of the charge movement. These results suggest that a part of the charge movement reflects the conformational change of the DHP receptors upon membrane depolarization.

Effect of SR33557 on intramembrane charge movement in normal and 'muscular dysgenesis' mouse skeletal muscle cells

It has been reported that the indolizinsulphone SR33557, which binds to a site on the alpha 1 subunit of the dihydropyridine receptor, blocks both L-type calcium channel activity and contraction in skeletal muscle. Moreover, we know that charge movement plays a key role in the mechanism of excitation-contraction coupling and in controlling the opening of L-type calcium channels. We demonstrate here that SR33557 reduces intramembrane charge movement in skeletal muscle from normal mice with an IC50 of approximately 10 nM. The drug does not completely inhibit charge movement since approximately 20% of total charge movement persists even in the presence of 30 microM SR33557. However, the SR33557-sensitive charge component is more important than the dihydropyridine-sensitive one. Surprisingly, SR33557 also reduces intramembrane charge movement in dysgenic myotubes which are characterized by a very strong reduction of the number of dihydropyridine binding sites. In these muscles, 10 microM SR33557 reduces approximately 40% of total charge movement. These observations suggest the presence of a new component of charge movement which is sensitive to SR33557 but insensitive to nifedipine. This component is also present in dysgenic myotubes, and it could be produced by the lower molecular weight alpha 1 subunit described by Malouf, N. N., McMahon, D. K., Hainsworth, C. N. and Kay, B. K. (1992) (Neuron, 8, 899-906).

Extracellular Ca(2+)-dependent and independent calcium transient in fetal myotubes

Spatio-temporal changes in the intracellular calcium concentration [Ca2+]i of dissociated mice myotubes from 14-day and 18-day-old fetuses were studied using digital imaging analysis of the Ca2+ indicator fura-2. Myotubes from 18-day-old fetuses displayed a transient [Ca2+]i increase upon electrical stimulation either in nominally calcium-free external solution or in Krebs solution containing 100 microM lanthanum. Thus, at this developmental stage, membrane depolarization appears to increase [Ca2+]i by stimulating Ca2+ release from the sarcoplasmic reticulum independently of extracellular Ca2+ influx. Similarly, myotubes from 14-day-old fetuses also showed a calcium transient upon electrical stimulation in Krebs solution. However, in 46% of these myotubes the calcium transient was abolished when Ca2+ entry through calcium channels was suppressed.

Anti-IgE induces the opening of non selective cation channels on human basophils

Basophils play a major role in allergic reactions-particularly in late phase reactions-by releasing histamine and other mediators of inflammation. Although transmembrane ion fluxes are thought to play an important role in the modulation of histamine release, little is known about ion pathways through the basophil membrane. We thus studied human basophils from normal subjects (n = 25 cells) with the patch-clamp method. We observed that IgE-dependent activation of human basophils led to the opening of non selective cation channels with a 20pS conductance. This was obtained when the patch pipette was applied onto the cell surface and sealed onto it in order to measure transmembrane currents on a small surface of intact basophils (cell-attached configuration). Non selective channels with the same 20pS conductance were also observed when a membrane patch was detached from basophil and its inner side placed in a Ca(2+)-containing medium (inside-out configuration). These data are a first contribution of the patch-clamp method in the understanding of ion movements in human basophils.

Charge movement and Ca2+ release in normal and dysgenic foetal myotubes

Intramembrane charge movement and Ca2+ release from sarcoplasmic reticulum was studied in foetal skeletal muscle cells from normal and mutant mice with 'muscular dysgenesis' (mdg/mdg). It was shown that: 1) unlike normal myotubes, in dysgenic myotubes membrane depolarization did not evoke calcium release from the sarcoplasmic reticulum; 2) when all ionic currents are pharmacologically suppressed, membrane depolarization produced an asymmetric intramembrane charge movement in both normal and dysgenic myotubes. The relationship between the membrane potential and the amount of charge movement in these muscles could be expressed by a two-state Boltzmann equation; 3) the maximum amount of charge movement associated with depolarization (Qon max) in normal and in dysgenic myotubes was 6.3 +/- 1.4 nC/microF (n = 6) and 1.7 +/- 0.3 nC/microF (n = 6) respectively; 4) nifedipine (1-20 microM) applied to the bath reduced Qon max by about 40% in normal muscle cells. In contrast, the drug had no significant effect on the charge movement of dysgenic myotubes; and 5) the amount of nifedipine-resistant charge movement in normal and in dysgenic myotubes was 3.5 nC/microF (n = 3) and 1.7 nC/microF 1 maximum (n = 3), respectively.

Ciguatoxin, extracted from poisonous morays eels, causes sodium-dependent calcium mobilization in NG108-15 neuroblastoma x glioma hybrid cells

Measurement of intracellular Ca2+ concentration ([Ca2+]i) in cultured mouse NG108-15 neuroblastoma x glioma hybrid cells, using the fluorescent probe fura-2, revealed that 5-25 nM ciguatoxin (CTX) increased [Ca2+]i either in cells bathed in standard medium or after removal of external Ca2+ by a Ca(2+)-free medium supplemented with EGTA. Tetrodotoxin prevented the CTX increased [Ca2+]i suggesting that CTX-induced mobilization of intracellular Ca2+ depends on Na+ influx through voltage-gated Na channels. CTX-induced Ca2+ mobilization prevented subsequent action of bradykinin (1 microM) suggesting that CTX stimulates the inositol 1,4,5-trisphosphate-releasable Ca2+ store.

Intramembrane charge movement in developing skeletal muscle cells from fetal mice

The development of intramembrane charge movement was studied in freshly isolated skeletal muscle cells from 13- to 19-day-old mouse fetuses. Charge movement was present in myotubes from 13-day-old fetuses. The relationship between charge movement and membrane potential could be described by a two-state Boltzmann equation. The amount of maximum charge movement (Qmax) increased substantially with the age of the fetuses from 2.84 +/- 0.39 nC/microF (n = 10) at day 13 to 10.01 +/- 0.97 nC/microF (n = 15) at day 19. Nifedipine (1 microM) consistently reduced Qmax by 33 +/- 2% (n = 37) of the control value at each age studied. Increasing the concentration of nifedipine to 20 microM had no further effect, suggesting that the charge movement in developing myotubes consists of at least two components: a nifedipine-sensitive charge movement (Qns) and a nifedipine-resistant one (Qnr). Both Qns and Qnr increased exponentially with a distinct enhancement of rate at day 16.

Regulation of human basophil activation. II. Histamine release is potentiated by K+ efflux and inhibited by Na+ influx

Na+ and K+ are the major extra- and intracellular cations, respectively. We have thus studied the role of these ions on human basophil histamine release by modifying their transmembrane gradients or by increasing membrane ion fluxes using ionophores. 1) When external Na+ (reduced to 4 mM) was replaced by the nonpermeating Na+ substitute N-methyl-D-glucamine, the release of histamine was enhanced in 2 mM Ca2+ (from 37.5 +/- 8.0% in 140 mM Na+ to 68.5 +/- 9.1% in low Na+) and became possible in the presence of low Ca2+ (at 1 microM Ca2+: from 0.6 +/- 0.7% in 140 mM Na+ to 36.2 +/- 8.0% in low Na+); moreover, in low Na+, the release of histamine became partly independent on Ca2+ influx. 2) Increasing the Na+ influx with the cation channel-forming gramicidin D inhibited the release of histamine by 33.2 +/- 13.6% (n = 6) in an external Na(+)-dependent manner. 3) Decreasing K+ efflux using K+ channel blockers (4-aminopyridine, quinine, sparteine) inhibited histamine release in a dose-response manner. 4) The K+ ionophore valinomycin, which increases K+ efflux, slightly enhanced IgE-mediated histamine release when used alone, whereas it potentiated the release of histamine from leukocytes previously treated with 4-aminopyridine by 57.0 +/- 18.6% (n = 7). 5) Decreasing K+ efflux by increasing external K+ inhibited IgE-mediated release in a similar manner as Na+ did. The inhibitory effects of Na+ and high K+ were not additive, thus suggesting that both cations inhibited the release by a common mechanism. In conclusion 1) our data evidence that histamine release from human basophils is inhibited by Na+ influx and potentiated by K+ efflux; 2) they suggest that K+ channels are present on the basophil membrane and that Na+ and K+ fluxes act on histamine release most probably via modulation of membrane potential.

Regulation of human basophil activation. II. Histamine release is potentiated by K+ efflux and inhibited by Na+ influx

Na+ and K+ are the major extra- and intracellular cations, respectively. We have thus studied the role of these ions on human basophil histamine release by modifying their transmembrane gradients or by increasing membrane ion fluxes using ionophores. 1) When external Na+ (reduced to 4 mM) was replaced by the nonpermeating Na+ substitute N-methyl-D-glucamine, the release of histamine was enhanced in 2 mM Ca2+ (from 37.5 +/- 8.0% in 140 mM Na+ to 68.5 +/- 9.1% in low Na+) and became possible in the presence of low Ca2+ (at 1 microM Ca2+: from 0.6 +/- 0.7% in 140 mM Na+ to 36.2 +/- 8.0% in low Na+); moreover, in low Na+, the release of histamine became partly independent on Ca2+ influx. 2) Increasing the Na+ influx with the cation channel-forming gramicidin D inhibited the release of histamine by 33.2 +/- 13.6% (n = 6) in an external Na(+)-dependent manner. 3) Decreasing K+ efflux using K+ channel blockers (4-aminopyridine, quinine, sparteine) inhibited histamine release in a dose-response manner. 4) The K+ ionophore valinomycin, which increases K+ efflux, slightly enhanced IgE-mediated histamine release when used alone, whereas it potentiated the release of histamine from leukocytes previously treated with 4-aminopyridine by 57.0 +/- 18.6% (n = 7). 5) Decreasing K+ efflux by increasing external K+ inhibited IgE-mediated release in a similar manner as Na+ did. The inhibitory effects of Na+ and high K+ were not additive, thus suggesting that both cations inhibited the release by a common mechanism. In conclusion 1) our data evidence that histamine release from human basophils is inhibited by Na+ influx and potentiated by K+ efflux; 2) they suggest that K+ channels are present on the basophil membrane and that Na+ and K+ fluxes act on histamine release most probably via modulation of membrane potential.

Barium currents in developing skeletal muscle cells of normal and mutant mice foetuses with 'muscular dysgenesis'

The ontogenesis of Ca channel activities was studied in the developing myotubes of normal mice and mutant mice foetuses with 'Muscular Dysgenesis'. The ionic current through Ca channels was measured with Ba2+ as charge carrier using the whole cell clamp technique. All dissociated myotubes from foetuses (14th to 18th day of gestation) showed two distinct inward Ba currents: a low threshold, transient current (T-type) and a high threshold sustained current. In normal myotubes, T-type current density increased from the 14th day to the 16th day of gestation. After day 16, T-type current density decreased gradually until birth. Similar changes in T-type current density were observed in developing dysgenic myotubes where the current density was about 40% of that measured in normal myotubes throughout the prenatal period studied. The high threshold sustained current (L-type current) density increased gradually with age in normal myotubes while absent in dysgenic muscle. The latter, regardless of age, showed a high threshold current (Idys) which is distinct from the L-type current. Idys density did not change during the prenatal myogenesis period studied.

Reduced intramembrane charge movement in the dysgenic skeletal muscle cell

Intramembrane charge movement in skeletal muscle cells has been proposed to underlie the process leading to Ca release from the sarcoplasmic reticulum. A number of recent studies suggest that the dihydropyridine receptor located in the transverse-tubular membrane is responsible for the generation of intramembrane charge movement. The skeletal muscle cell of the mutant mouse with "Muscular Dysgenesis" is characterized by absence of excitation-contraction coupling. Here we investigated the charge movement in freshly dissociated skeletal muscle cells from dysgenic mice. In 9 out of 34 dysgenic mouse cells the charge movement was completely absent, in the remaining cells the charge movement was never more than 30% of control. The amount of maximum charge movement (Qmax) in mutant muscle cells was less than 30% of Qmax in normal muscle. Nifedipine, a dihydropyridine derivative, reduced the amount of charge movement in normal muscle cells but it was less effective on charge movement in mutant muscle cells. We conclude that there is an alteration of nifedipine-sensitive charge movement in the skeletal muscle cells from the mutant mice.

Mobilization of intracellular Ca2+ and suppression of inward currents in a neuronal hybrid cell line triggered by bradykinin

Bradykinin triggered intracellular Ca mobilizations and ionic conductance changes were studied in the neuroblastoma x glioma hybrid cell line NG108-15 using Ca-sensitive fluorescent indicator fura-2 under patch pipette whole cell voltage clamp condition. The time course of outward current induced by bradykinin was closely related to the time-course of [Ca2+]i change. Following application of bradykinin, [Ca2+]i increased transiently and then decreased below the basal level before bradykinin application. The inward currents activated by step-depolarization were suppressed after bradykinin application, but the time-course of the suppression did not go in parallel with the [Ca2+]i changes: the suppression started before the [Ca2+]i change emerged and outlasted the phase of [Ca2+]i increase. Both transient type and long-lasting type Ca current were suppressed by bradykinin. [Ca2+]i increase induced by high potassium depolarization was suppressed by bradykinin. Pertussis toxin did not affect the Ca transient nor the suppression of Ca channel induced by bradykinin. Our results suggest that the modifications of ionic channels by bradykinin could be through the other mechanisms than the well established activation of the G-protein leading to the IP3 mechanisms and that the bradykinin receptor might couple with the pertussis toxin-insensitive G protein which regulates the calcium channels.

Appearance of the slow Ca conductance in myotubes from mutant mice with "muscular dysgenesis"

Voltage gated Ca conductance in skeletal muscle cells from mice with muscular dysgenesis (mdg/mdg) and from normal mice was studied using the whole cell recording technique. The physiological properties of the myotubes from the mutant mice (uncoupling of excitation-contraction, deficiency in the voltage gated slow Ca conductance) were changed to normal when the mdg/mdg myotubes were cocultured with spinal cord cells from normal mice. Spinal cord cells from mutant mice failed to induce normal muscle activity in the mutant myotubes. In aged mutant myotubes cultured without spinal cord cells, the slow Ca conductance sometimes developed, although with smaller amplitude. The number of mdg/mdg myotubes with partial development of the slow Ca conductance increased with the age of the culture. E-C coupling was never established in aged mutant myotubes. The phenotypic reversion did not require functional synaptic transmission since it was also obtained when neuromuscular transmission was chronically blocked with alpha-bungarotoxin (4-40 micrograms/ml).

Ionic currents in neurones cultured from embryonic cockroach (Periplaneta americana) brains

Neurones isolated from embryonic cockroach brains were maintained in culture for up to 8 weeks. A single patch electrode was used to record voltage changes in response to injected current, membrane ionic currents under whole-cell voltage-clamp conditions or single-channel currents from isolated membrane patches. The voltage changes in response to injected current that depolarized the cell indicated increases in membrane permeability to calcium and potassium. These observations were confirmed using a voltage clamp. The potassium current observed in the youngest cultures turned on with a delay and was blocked by tetraethylammonium (TEA) and 4-aminopyridine (4-AP). Two kinds of decrease in the outward potassium current were observed. One may be associated with extracellular potassium accumulation, inactivation of the potassium channel or inactivation of a calcium channel. The other appears to be a voltage-dependent inactivation. The magnitude of the calcium permeability appeared to increase as the cultures developed, being most prominent in cultures more than 2 weeks old. Single-channel conductance measured from an analysis of records from six isolated membrane patches ranged from 15 to 110 pS. Except for one channel, the probability of the channels being open did not change appreciably with membrane potential. Our results suggest that much of the increase in potassium permeability may be due an increase in intracellular calcium level.

Restoration of dysgenic muscle contraction and calcium channel function by co-culture with normal spinal cord neurons

Muscular dysgenesis (mdg) is a spontaneous recessive lethal mutation in the mouse. The disease is characterized by a total lack of excitation-contraction coupling in embryonic skeletal muscle. This developmental abnormality is associated with a drastic deficiency in the expression of voltage-sensitive Ca2+ channels in skeletal muscle without alteration of the properties of voltage-sensitive Na+ channels or of voltage-sensitive Ca2+ channels in cardiac and neuronal cells. Membrane couplings between sarcoplasmic reticulum and the transverse tubules, known as triads, were also found to be drastically altered in embryonic muscle of the homozygous mutant (mdg/mdg). Triads in the mdg/mdg muscle were less numerous, disorganized and lacked spaced densities. This paper shows that co-culture of mdg/mdg myotubes with normal spinal cord neurons re-establishes Ca2+ channel activity, contraction and normal triad organization. The decrease thus cannot be due to a mutation of the Ca2+ channel as previously suggested. Normal nerve cells may supply an essential factor to mutant muscle cells.

Activation of enkephalin receptors reduces calcium conductance in neuroblastoma cells

Enkephalin actions on the voltage-gated Ca channel were studied under voltage clamp in the neuroblastoma X glioma hybrid cell line, NG 108-15. We found that in sodium-free external solutions containing Ba2+ (20 mM), a depolarizing step pulse from a holding potential of -50 mV evoked both a rapidly decaying inward current and a sustained inward current similar to those described in other preparations. External application of 1 microM [D-Thr2,Leu5]enkephalin-Thr (DTLET), an agonist at the delta-opioid receptors specifically inhibited the sustained inward current. Naloxone, an antagonist at this receptor, blocked the effect of DTLET. Furthermore, this effect of DTLET was not observed if the cells were dialyzed with a low Ca2+ internal buffer solution [( Ca2+]i less than 10(-9) M). We conclude that in neuroblastoma cells: (1) there is a functional coupling between delta-receptors and voltage-gated sustained Ca channels, and (2) the coupling is mediated by intracellular free Ca ions.

Acetylcholine-activated currents in mouse neuroblastoma cells

The nicotine and muscarinic responses of differentiated mouse neuroblastoma cells from the clonal line N1E 115 to applied cholinergic agents were recorded using single channel and whole cell patch clamp techniques. An inward macroscopic current induced by acetylcholine (ACh) at the resting potential was blocked by curare; cell-attached recordings revealed a single channel conductance of 18 pS and a lifetime of 36 ms at 30 degrees C, with 200 nM ACh. The zero current potential was close to 0 mV. The kinetics of these nicotinic currents were described by multiexponential functions for both the open and closed time distributions. An outward single channel current, present at resting and slightly depolarized potentials, was also observed and has been tentatively described as being dependent on muscarinic receptor activation, as it was usually blocked by atropine. Under our conditions of whole cell clamp, no macroscopic outward current sensitive to ACh was observed.

Arsenazo III transients and calcium current in a normally non-spiking neuronal soma of crayfish

Arsenazo III was used to investigate Ca2+ transients in the normally non-excitable soma of the motor giant neurones of the crayfish Procambarus clarkii. Two kinds of regenerative potentials could be obtained depending on membrane potential conditioning: a fast spike after a pre-hyperpolarization to -90 mV and a slow action potential after a pre-depolarization to -50 mV. Only the second of these was accompanied by an Arsenazo III transient. In voltage-clamped, somata injected, with tetraethylammonium chloride, an absorbance change could be obtained by pulsing the membrane potential above -44 mV. The relationship between absorbance change and potential peaked between 0 and +10 mV then fell off to zero at ca. +150 mV. Changes in light absorbance studied using double-pulse protocols suggested that the inactivation of Ca2+ entry was predominantly mediated by the intracellular free Ca2+ concentration. External application of 1 mM-CdCl2 abolished both the absorbance changes and the (Ca2+) inward current. The voltage dependence of this current was similar to that of the absorbance change. For positive membrane potential the current-voltage relationship showed a voltage-dependent conductance property, the origin of which is discussed.

Presynaptic modulation of transmitter release by the early outward potassium current in Aplysia

The mechanism involved in presynaptic modulation of transmitter release was studied in an identified synapse of Aplysia californica. Presynaptic hyperpolarization induces a decrease in he evoked postsynaptic potential amplitude. This is shown to be due to a reduction in the presynaptic spike amplitude during the hyperpolarization. The decreased presynaptic spike amplitude with hyperpolarization is explained s resulting from the superimposition of an early outward potassium current on the transient inward current. It is suggested that the presynaptic hyperpolarizing conditioning pulse decreases inactivation of the early outward current, which shunts the transient inward current. The superimposition of these two currents (transient inward current and the early outward current) induces a decrease in presynaptic spike amplitude, which in turn reduces the synaptic output from the terminal.

Modulation of synaptic output by the transient outward potassium current in aplysia

The mechanisms involved in synaptic output modulation by presynaptic membrane potential was studied in identified Aplysia synapses, where a presynaptic hyperpolarization reduces the postsynaptic potential amplitude. The experiment reported here reveals that a presynaptic conditioning hyperpolarization induces a decreased presynaptic spike amplitude and that the reduction is due to a superimposition of a transient outward potassium current on the inward current. This is demonstrated by the external application of 4-aminopyridine which suppresses the early outward current and thus suppresses the modulation both of the presynaptic spike amplitude and the synaptic output.

Quantal transmitter release in an identified inhibitory cholinergic synapse of Aplysia

A sustained postsynaptic potential is observed in an identified synapse of Aplysia when the presynaptic neuron is depolarized in the presence of tetrodotoxin (TTX). This prolonged postsynaptic potential appears to be at least in part due to the summation of quantal events. It is still observed when 30 mM CoCl2, which is known to inhibit Ca2+ influx, is added to the external media.

Multiple interneuronal afferents to the giant cells in Aplysia

1. Several different types of presynaptic neurones to the giant cells of Aplysia have been found in the pleural ganglion. Some of these presynaptic neurones are common to the left giant cell in the pleural ganglion and to the right giant cell in the abdominal ganglion but others make contact only with one. 2. Interneurones of the left giant cell were studied in detail. They can be identified not only physiologically from the type of post-synapitc potential (p.s.p.) which they produce in the left giant cell, but also by their localization in the ganglion. 3. Direct stimulation of these presynaptic neurones produced not only the classical types of post-synaptic potentials known as e.p.s.p. or i.p.s.p. but also a slow e.p.s.p. and more complex post-synaptic potentials consisting of a rapid depolarizing or hyperpolarizing component (e for excitatory; i for inhibitory). According the p.s.p.s. which have been found were classified as being of eight different types: e.p.s.p., slow e.p.s.p., pseudo-slow e.p.s.p., e.i.p.s.p., i.e.p.s.p., i.i.p.s.p., to which is added the biphasic p.s.p. (b.p.s.p.) of electrical origin. 4. The monosynaptic nature of each of these p.s.p.s. was established by four criteria: (a) ability to follow one to one the presynaptic spike, (b) short and constant latency, (c) change of p.s.p. with the presynaptic spike when the duration is prolonged by iontophoretic injection of TEA, (d) sensitivity of the synaptic efficacy to presynaptic polarization. 5. For all p.s.p.s., the hyperpolarization of the interneurone was followed by a decrease in the corresponding amplitude; on the contrary depolarization produced an increase in p.s.p. amplitude. 6. The physiological role of these p.s.p.s. and their possible mechanism are discussed.

Heterosynaptic facilitation in the giant cell of Aplysia

1. Heterosynaptic facilitation, defined as an increase of the efficacy of synaptic transmission between a test interneurone and a post-synaptic neurone, produced by the stimulation of a separate pathway, was studied in the left pleural ganglion. The experimental procedure consisted of detecting the effects of a brief tetanus, applied to tentacular and tegumentary nerves, on the amplitude of monosynaptic and unitary post-synaptic potentials (p.s.p.s) recorded in the left giant cell and generated by stimulating the test interneurone every 10 sec. The membrane potential of the test interneurone was simultaneously recorded. 2. Following heterosynaptic stimulation, the amplitude of the test p.s.p. increased, after a delay of about 30 sec, up to 250% of its original size; this increase subsided after 2-3 min or more. 3. Only the interneurones producing in the giant cell the e.i.p.s.p. (excitatory-inhibitory post-synaptic potential) were affected by hetero-synaptic facilitation. Other interneuronal types showed no changes in their synaptic transmission on the giant cell after heterosynaptic stimulation. 4. Heterosynaptic stimulation did not produce either orthodromic or antidromic spikes in the test interneurones clearly indicating that facilitation of test p.s.p. did not result from increased spike activity in the test interneurone. 5. Often heterosynaptic facilitation of the test p.s.p. was observed due to spontaneous activity in the heterosynaptic pathway, demonstrating the normal occurrence of the phenomenon. 6. Iontophoretic injection of 5-HT at critical, presumably synaptic, sites in the neuropil, evoked a facilitation of the test p.s.p. similar to heterosynaptic facilitation. Only the e.i.p.s.p.s. were so affected by 5-HT. On the contrary, other p.s.p. types were depressed by 5-HT as a result of conductance changes in the left giant cells. 7. Both heterosynaptic facilitation and 5-HT facilitation were suppressed by the presence in the bath of 5-HT (10(-5) M) and of LSD-25 (3 X 10(-4) M). The action of injected 5-HT on the membrane conductance of the left giant cell was also depressed in the pressence of 5-HT in the bath, but was unaffected by LSD-25 (3 X 10(-4) M). 8. From the parallelism of properties of heterosynaptic and 5-HT facilitation, it is suggested that 5-HT is the probable transmitter mediating heterosynaptic facilitation. It seems likely that 5HT is released from the heterosynaptic pathway at the level of the synaptic ending of the test interneurone on to the giant cell and that it increases the efficacy of this synapse, probably acting on the quantity of synaptic transmitter liberated.

Salivary, serum, and microbial components of human carious dentin

By use of immunohistochemical staining methods, salivary and serum components, ie, γ-globulin and serum albumin, were found in sound and carious human dentin. Most notable reactions were observed in dentinal tubules beneath a translucent zone (radiopaque zone) in carious dentin. Oral microorganisms also were found in soft carious dentin.