Retrospective Pathological Studies of Splenic Lesions in Domestic Hamsters (Phodopus spp.)

Fifteen splenic biopsy specimens from a total of 212 biopsy specimens and necropsy cases of domestic hamsters (Phodopus spp.) from the Division of Wild (Exotic) Animal Medicine, Veterinary Medical Teaching Hospital, National Chung Hsing University, Taiwan, collected between 2010 and 2017, were studied retrospectively. The incidence of lesions in the spleen was 7.1% (15/212). The mean age of affected hamsters was 16.6 months and females were affected more than males. The lesions consisted of 10 neoplasms and five non-neoplastic lesions. The most common tumours were histiocytic sarcoma (HS), lymphoma, malignant fibrous histiocytoma (MFH) and hemangiosarcoma. Immunohistochemistry revealed the HSs and MFHs to express lysozyme. The lymphomas were negative for CD20; however, one case was positive for CD3 and another was positive for CD79a. The hemangiosarcoma expressed von Willebrand factor. The non-neoplastic lesions were all fibrotic nodules and these were all identified in ageing female hamsters. The nodules consisted of collagen fibres identified with Masson's trichrome stain, and they were related to repair of trauma in the spleen.

Compartmentalized and binary behavior of terminal dendrites in hippocampal pyramidal neurons

The dendritic arbor of pyramidal neurons is not a monolithic structure. We show here that the excitability of terminal apical dendrites differs from that of the apical trunk. In response to fluorescence-guided focal photolysis of caged glutamate, individual terminal apical dendrites generated cadmium-sensitive all-or-none responses that were subthreshold for somatic action potentials. Calcium transients produced by all-or-none responses were not restricted to the sites of photolysis, but occurred throughout individual distal dendritic compartments, indicating that electrogenesis is mediated primarily by voltage-gated calcium channels. Compartmentalized and binary behavior of parallel-connected terminal dendrites can greatly expand the computational power of a single neuron.

A novel Ca(2+) influx pathway in mammalian primary sensory neurons is activated by caffeine

Single-cell microfluorimetry and electrophysiology techniques were used to identify and characterize a novel Ca(2+) influx pathway in adult rabbit vagal sensory neurons. Acutely dissociated nodose ganglion neurons (NGNs) exhibit robust Ca(2+)-induced Ca(2+) release (CICR) that can be triggered by 10 mM caffeine, the classic agonist of CICR. A caffeine-induced increase in cytosolic-free Ca(2+) concentration ([Ca(2+)](i)) is considered diagnostic evidence of the existence of CICR. However, when CICR was disabled through depletion of intracellular Ca(2+) stores or pharmacological blockade of intracellular Ca(2+) release channels (ryanodine receptors), caffeine still elicited a significant rise in [Ca(2+)](i) in approximately 50% of NGNs. The same response was not elicited by pharmacological agents that elevate cyclic nucleotide concentrations. Moreover, extracellular Ca(2+) was obligatory for such caffeine-induced [Ca(2+)](i) rises in this population of NGNs, suggesting that Ca(2+) influx is responsible for this rise. Simultaneous microfluorimetry with whole cell patch-clamp studies showed that caffeine activates an inward current that temporally parallels the rise in [Ca(2+)](i). The inward current had a reversal potential of +8.1 +/- 6.1 (SE) mV (n = 4), a mean peak amplitude of -126 +/- 24 pA (n = 4) at E(m) = -50 mV, and a slope conductance of 1.43 +/- 0.79 nS (n = 4). Estimated EC(50) values for caffeine-induced CICR and for caffeine-activated current were 1.5 and approximately 0.6 mM, respectively. These results indicate that caffeine-induced rises in [Ca(2+)](i), in the presence of extracellular Ca(2+), can no longer be interpreted as unequivocal diagnostic evidence for CICR in neurons. These results also indicate that sensory neurons possess a novel Ca(2+) influx pathway.

Estradiol enhances excitatory gamma-aminobutyric [corrected] acid-mediated calcium signaling in neonatal hypothalamic neurons

Contrary to the situation in adulthood, gamma-aminobutyric [corrected] acid (GABA)(A) receptor activation during early brain development depolarizes neurons sufficiently to open L-type voltage-gated Ca(2+) channels. Because GABA is excitatory during the sensitive period of steroid-mediated brain sexual differentiation, we investigated whether estradiol modulates excitatory GABA during this period, by examining two parameters: 1) magnitude of GABA-induced calcium transients; and 2) developmental duration of excitatory GABA. Dissociated hypothalamic neurons from embryonic-day-15 rat embryos were loaded with the Ca(2+) indicator, fura-2, and transient rises in [Ca(2+)](i) (Ca(2+) transient) were measured after application of 10 microM muscimol, a GABA(A) receptor agonist. Cells were treated with 10(-10) M estradiol or vehicle from 0-3 days in vitro (DIV) and imaged on 4 DIV, whereas others were treated from 3-6 DIV and imaged on 7 DIV. The mean amplitude of Ca(2+) transients after muscimol administration were 68% and 61% higher in estradiol-treated neurons on 4 DIV and 7 DIV, respectively, relative to controls. Consistent with GABA becoming inhibitory in mature neurons, 50% fewer control neurons responded on DIV 7, relative to DIV 4. However, estradiol treatment maintained excitatory GABA on DIV 7 (72% in estradiol-treated vs. 35% in control). This is the first report of hormonal modulation of excitatory GABA, and it suggests that estradiol may mediate sexual differentiation by enhancing GABA-induced increases in intracellular Ca(2+).

Enterotoxicity and cytotoxicity of Vibrio parahaemolyticus thermostable direct hemolysin in in vitro systems

Vibrio parahaemolyticus is a marine bacterium known to be a common cause of seafood gastroenteritis worldwide. The thermostable direct hemolysin (TDH) has been proposed to be a major virulence factor of V. parahaemolyticus. TDH causes intestinal fluid secretion as well as cytotoxicity in a variety of cell types. In this study, we investigated the interplay between the hemolysin's enterotoxic and cytotoxic effects by using both human and rat cell monolayers. As revealed by microspectrofluorimetry, the toxin causes a dose-dependent increase in intracellular free calcium in both Caco-2 and IEC-6 cells. This effect was reversible only when low toxin concentrations were tested. The TDH-activated ion influx pathway is not selective for calcium but admits ions such sodium and manganese as well. Furthermore, in the same range of concentration, the hemolysin triggers a calcium-dependent chloride secretion. At high concentrations, TDH induces a dose-dependent but calcium-independent cell death as assessed by functional, biochemical, and morphological assays.

Organization of intracortical circuits in relation to direction preference maps in ferret visual cortex

Neurons in the primary visual cortex are selective for the direction of movement of a visual stimulus. Like other stimulus features, direction preference is mapped on the cortical surface in a systematic manner. Intracortical synaptic circuits, in particular inhibitory connections, have been implicated in the emergence of direction selectivity. Whether intracortical inhibition specifically suppresses responses to the nonpreferred direction or has a nonspecific "thresholding" effect is still controversial. To address these questions we investigated the relationship between patterns of intracortical synaptic connections and direction domains in ferret primary visual cortex (area 17) using a combined in vivo-in vitro approach. Excitatory synaptic inputs were iso-direction-tuned. The majority of local inhibitory inputs were also iso-direction-tuned. However, approximately 40% of inhibitory connections originated in regions preferring the opposite direction. These findings indicate that specific inhibitory interactions between cortical regions of opposite direction preference may contribute to the emergence and sharpening of direction selectivity.

Calcium regulation of a slow post-spike hyperpolarization in vagal afferent neurons

Activation of distinct classes of potassium channels can dramatically affect the frequency and the pattern of neuronal firing. In a subpopulation of vagal afferent neurons (nodose ganglion neurons), the pattern of impulse activity is effectively modulated by a Ca2+-dependent K+ current. This current produces a post-spike hyperpolarization (AHPslow) that plays a critical role in the regulation of membrane excitability and is responsible for spike-frequency accommodation in these neurons. Inhibition of the AHPslow by a number of endogenous autacoids (e.g., histamine, serotonin, prostanoids, and bradykinin) results in an increase in the firing frequency of vagal afferent neurons from <0.1 to >10 Hz. After a single action potential, the AHPslow in nodose neurons displays a slow rise time to peak (0.3-0.5 s) and a long duration (3-15 s). The slow kinetics of the AHPslow are due, in part, to Ca2+ discharge from an intracellular Ca2+-induced Ca2+ release (CICR) pool. Action potential-evoked Ca2+ influx via either L or N type Ca2+ channels triggers CICR. Surprisingly, although L type channels generate 60% of action potential-induced CICR, only Ca2+ influx through N type Ca2+ channels can trigger the CICR-dependent AHPslow. These observations suggest that a close physical proximity exists between endoplasmic reticulum ryanodine receptors and plasma membrane N type Ca2+ channels and AHPslow potassium channels. Such an anatomical relation might be particularly beneficial for modulation of spike-frequency adaptation in vagal afferent neurons.

Ca2+-induced Ca2+ release mediates a slow post-spike hyperpolarization in rabbit vagal afferent neurons

The relation between Ca2+-induced Ca2+ release (CICR) elicited by action potentials (APs) and a Ca2+-dependent slow post-spike hyperpolarization (AHPslow) in acutely dissociated adult rabbit nodose neurons was studied using microfluorimetric calcium measurements in conjunction with standard intracellular current- and voltage-clamp recording techniques. The magnitude of the AP-induced transient increase in [Ca2+]i (DeltaCat) was used to monitor CICR. There was a close correlation between the magnitude of the DeltaCat and the AHPslow current over the range of 1-16 APs (r = 0.985). Functional CICR blockers, ryanodine (10 muM), thapsigargin (100 nM), 2,5-di(t-butyl)hydroquinone (10 muM) or cyclopiazonic acid (10 muM), selectively reduced the peak amplitude of the AHPslow >/=91%. In five neurons, simultaneous recordings of the DeltaCat and the AHPslow revealed that both responses were blocked in parallel. These findings indicate that CICR is necessary for the generation of the AHPslow in rabbit nodose neurons. The DeltaCat rises and decays significantly faster than the AHPslow. This temporal disparity suggests that activation of the AHPslow by Ca2+ may require additional signal transduction steps.

N-Nmoc-L-glutamate, a new caged glutamate with high chemical stability and low pre-photolysis activity

We report the synthesis, the physicochemical characterization, and biological evaluation of a new caged glutamate, N-(o-nitromandelyl)oxycarbonyl-L-glutamic acid (Nmoc-Glu), that liberates free glutamate on photolysis. The low affinity of certain glutamate receptors and their rapid entry into desensitization have effectively prevented the creation of an ideal caged glutamate. In the absence of an ideal compound, Nmoc-Glu was designed to resist spontaneous hydrolysis while maintaining reasonable photorelease yield and kinetics. Chemical and physiological analyses reveal that Nmoc-Glu, indeed, has exceptionally low residual activity and high chemical stability. The quantum yield of Nmoc-Glu is 0.11. Photolytic uncaging and release of free glutamate occur in two steps, consisting of an initial light-induced cleavage that proceeds on the sub-millisecond time scale, and a subsequent light-independent, pH-dependent decarboxylation step that proceeds on the millisecond time scale. The low residual activity and high chemical stability of Nmoc-Glu are important advantages in applications where pre-photolysis Glu receptor activation and desensitization must be minimized.

Practical method for the multigram separation of the 5- and 6-isomers of carboxyfluorescein

An efficient preparative method for separating 5- and 6-carboxyfluorescein is presented. 6-Carboxyfluorescein dipivalate is isolated as its diisopropylamine salt, which can be converted to the free acid or used directly in coupling reactions. The 5-isomer is isolated from the acidified mother liquor. Isomerically pure carboxyfluoresceins are prepared by hydrolysis of the corresponding dipivalates.

Ca(2+)-induced Ca2+ release mediates Ca2+ transients evoked by single action potentials in rabbit vagal afferent neurones

1. Standard intracellular recording techniques with 'sharp' micropipettes were used to evoke action potentials (APs) in acutely dissociated adult nodose neurones. 2. APs induced a transient increase in [Ca2+]i (a calcium transient), recorded with fura-2, that was dependent upon [Ca2+]o and the number of APs. Over the range of one to sixty-five APs, the relation between the amplitude of the calcium transient and the number of APs was well fitted by a rectangular hyperbola (chi 2 = 3.53, r = 0.968). From one to four APs, the calcium transient-AP relation can be described by a line with a slope of 9.6 nM AP-1 (r = 0.999). 3. Charge movement corresponding to Ca2+ influx evoked by a single AP was 39 +/- 2.8 pC (mean +/- S.E.M.) and did not change significantly during trains of one to thirty-one APs (P < 0.05). 4. Caffeine (10 mM), a known agonist of the ryanodine receptor, produced an increase in [Ca2+]i. The caffeine-induced rise in [Ca2+]i was attenuated (by > 90%) by lowering [Ca2+]o, and by ryanodine (10 microM), 2,5-di(t-butyl)hydroquinone (DBHQ, 10 microM), or thapsigargin (100 nM). 5. Neurones incubated with ryanodine, DBHQ or thapsigargin required at least eight APs to evoke a detectable calcium transient. These reagents did not significantly affect Ca2+ influx (P < 0.05). In the presence of these inhibitors, the calcium transient-AP relation exhibited slopes of 1.2, 1.1 and 1.9 nM AP-1 for ryanodine, DBHQ and thapsigargin, respectively. When compared with the slope of 9.6 nM AP-1 in non-treated neurones, it appears that Ca2+ influx produced by a single AP is amplified by ca 5- to 10-fold.

Nmoc-DBHQ, a new caged molecule for modulating sarcoplasmic/endoplasmic reticulum Ca2+ ATPase activity with light flashes

We report the synthesis and characterization of O[o-nitromandelyloxycarbonyl]-2,5-di(tert-butyl)hydroquinone (Nmoc-DBHQ), a new "caged" reagent for photoreleasing DBHQ, a membrane-permeant, reversible inhibitor of the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA). The Nmoc group is a new caging group developed for the current application. Photolysis of Nmoc-DBHQ proceeds with t1/2 = 126 +/- 2 micros, and t1/2 for subsequent release of DBHQ is estimated to be approximately 5 ms. Nmoc-DBHQ thus allows rapid and reversible modulation of SERCA activity in living cells. Through its acetoxymethyl ester, Nmoc-DBHQ can be loaded into cells easily by incubation. We demonstrate the use of Nmoc-DBHQ for photomodulating SERCA activity in fibroblasts and vagal sensory neurons. We further demonstrate the utility of pulsed DBHQ photorelease for probing and manipulating dynamic phenomena such as [Ca2+] oscillations in fibroblasts.

Dopamine withdrawal elicits prolonged calcium rise to support prolactin rebound release

Dopamine (DA) acts directly on pituitary lactotropes to inhibit the release of PRL. Removal of DA elicits a pronounced transient rise in PRL release to values exceeding pre-DA rates (PRL rebound). Electrophysiological studies have shown that lactotropes exhibit a period of increased Ca2+ action potential activity after DA withdrawal, leading to the proposal that enhanced Ca2+ influx during this period may support the rebound secretion of PRL. In the present studies, we investigated the effect of DA application and removal on the cytosolic free calcium concentration ([Ca2+]i) monitored by fura-2 in single rat lactotropes. Unchallenged lactotropes fell into two functionally distinct groups: those with stable [Ca2+]i that was not acutely sensitive to extracellular Ca2+, and those with spontaneous fluctuations in [Ca2+]i that were dependent upon influx of external Ca2+. There was striking variability in the [Ca2+]i patterns of the latter group, ranging from irregular, low amplitude fluctuations to rhythmic, repetitive oscillations with definable rise and decay kinetics. Application of DA resulted in a rapid decrease in [Ca2+]i concomitant with the cessation of these spontaneous [Ca2+]i fluctuations. After DA removal, these cells resumed oscillatory [Ca2+]i activities similar to those observed before DA application. In quiescent lactotropes, acute application of DA exerted no effect on resting [Ca2+]i, but quiescent cells could be activated to produce [Ca2+]i fluctuations by the application and withdrawal of DA. Again, the character of the induced [Ca2+] activity showed significant cell to cell variation. In contrast, the pattern of [Ca2+]i fluctuations was remarkably characteristic in a given cell in response to repeated challenges. A composite [Ca2+]i profile of 13 cells paralleled the PRL secretory rebound after application and removal of DA. The oscillatory rise in [Ca2+]i is functionally linked to the rebound release of PRL after DA removal, as both were immediately abolished by blockade of Ca2+ influx. These data demonstrate that the rebound secretion of PRL is dependent upon enhanced influx of extracellular Ca2+ after cells recover from DA-induced hyperpolarization and support the hypothesis that a population of inactivated Ca2+ channels has been recruited in response to application and withdrawal of DA.

Calcium-dependent intestinal chloride secretion by Vibrio parahaemolyticus thermostable direct hemolysin in a rabbit model

BACKGROUND & AIMS

Vibrio parahaemolyticus is a major agent of seafood gastroenteritis that induces intestinal secretion in the rabbit through its thermostable direct hemolysin. The aim of this study was to characterize the enterotoxicity of purified hemolysin in vitro.

METHODS

Rabbit ileum was mounted in Ussing chambers, and changes in potential difference and short-circuit current were monitored after addition of hemolysin. Intracellular calcium concentrations in the nontumoral rat crypt-derived cell line IEC-6 were measured using microspectrofluorometry.

RESULTS

In Ussing chamber experiments, mucosal toxin addition up to 50 hemolytic units per milliliter induced a proportional increase of the electrical parameters in normal but not Cl(-)-free Ringer's solution. The response to the toxin was not additive to that of calcium ionophore A23187 and was eliminated by preloading the tissue with 1-2-bis(o-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA), a calcium buffer. In IEC-6 cells, a 10-fold increase in intracellular calcium level was found after addition of hemolysin. Such an increase was totally quenched by BAPTA. Finally, preincubation with trisialoganglioside GT1b, but not monosialoganglioside GM1, eliminated toxin-induced increases in potential difference and short-circuit current.

CONCLUSIONS

These data support the hypothesis that the thermostable direct hemolysin induces intestinal chloride secretion using GT1b as a putative receptor and Ca2+ as a second messenger.

Long-term depression in cerebellar Purkinje neurons results from coincidence of nitric oxide and depolarization-induced Ca2+ transients

The role of nitric oxide (NO) in the induction of long-term depression (LTD) in the cerebellum was explored using a new, organic, membrane-impermeant form of caged NO. NO photolytically released inside Purkinje neurons mimicked parallel fiber (PF) activity in synergizing with brief postsynaptic depolarization to induce LTD. Such LTD required a delay of < 50 ms between the end of photolysis and the onset of depolarization, was prevented by intracellular Ca2+ chelation, and was mutually occlusive with LTD conventionally produced by PF activation plus depolarization. Bath application of NO synthase inhibitor or of myoglobin, a NO trap, prevent LTD induction via PF stimulation, but not that from intracellular uncaged NO, whereas intracellular myoglobin blocked both protocols. NO is therefore an anterograde transmitter in LTD induction. A biochemical requirement for simultaneous NO and elevation of intracellular free Ca2+ would explain why PF activity must coincide with postsynaptic action potentials.

Nitric oxide regulates spike frequency accommodation in nodose neurons of the rabbit

A Ca(2+)-dependent slow spike after hyperpolarization (AHPslow) is present in about 35% of the neurons in the nodose ganglion. Although the AHPslow profoundly affects spike frequency accommodation of these neurons, the mechanisms that control the generation and the duration of the AHPslow are unclarified. N omega-Nitro-L-arginine methyl ester (L-NAME; 10 microM), a specific inhibitor of nitric oxide synthase (NOS), reduced the AHPslow by more than 92%. The L-NAME block of the AHPslow was antagonized by application of 50 microM S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide donor. The fast, Ca(2+)-dependent, spike after hyperpolarization preceding the AHPslow and the elevation of intracellular Ca2+ accompanying the AHPslow were unaffected by L-NAME treatment. These findings indicate that products of NOS activity might directly or indirectly activate the AHPslow K+ channels at a step beyond Ca2+ influx or intracellular Ca2+ mobilization.

Does the use of DM-nitrophen, nitr-5, or diazo-2 interfere with the measurement of indo-1 fluorescence?

Emission spectra of the photolabile Ca2+ chelators DM-nitrophen, nitr-5, and diazo-2 were studied alone, and in the presence of indo-1, to investigate potential interactions that would make the simultaneous manipulation and ratiometric measurement of the intracellular Ca2+ concentration difficult. Neither diazo-2 nor its photoproduct were found to be significantly fluorescent, and consequently concentrations of diazo-2 up to 20 times that of indo-1 did not distort the emission spectra of indo-1. DM-nitrophen was scarcely fluorescent, but its fluorescence did increase upon photolysis. In contrast to diazo-2 and DM-nitrophen, nitr-5 itself was found to be quite fluorescent, and this fluorescence was significantly increased upon photolysis. Thus, combined use of nitr-5 and indo-1 poses the most difficulty. The emission spectra of all the investigated compounds were used to define experimental conditions and calibration procedures that make possible simultaneous measurement and manipulation of the intracellular Ca2+ concentration.

Ligand-induced internalization and increased cell calcium are mediated via distinct structural elements in the carboxyl terminus of the epidermal growth factor receptor

Signals that can mediate ligand-induced receptor internalization and calcium regulation are present in a 48-amino acid "calcium-internalization" domain in the C' terminus of the epidermal growth factor (EGF) receptor. The basis of calcium and internalization regulation signalled by this 48-amino acid sequence was analyzed using deletion and substitution mutant receptors. Cells expressing truncated receptors containing either the NH2- or COOH-terminal portion of the 48-residue domain displayed high affinity EGF-dependent endocytosis and receptor down-regulation. These endocytosis-competent EGF receptor mutants that lacked any autophosphorylation site were unable to increase the concentration of intracellular calcium. To investigate the role of self-phosphorylation in EGF-induced calcium mobilization, phenylalanine was substituted for the single autophosphorylated tyrosine residue in this region of an internalization-competent truncated receptor. The receptor-mediated calcium response was abolished, while ligand-dependent receptor internalization was unimpaired. These results demonstrate that EGF-dependent receptor endocytosis and calcium mobilization are separate events. Tyrosine self-phosphorylation is required for increased [Ca2+]i, while structural features distinct from autophosphorylation are required for receptor internalization.

Cytosolic Ca2+ oscillations in REF52 fibroblasts: Ca(2+)-stimulated IP3 production or voltage-dependent Ca2+ channels as key positive feedback elements

Oscillations in cytosolic free calcium concentrations ([Ca2+]i) can be elicited in REF52 fibroblasts by three different modes of stimulation. We have previously demonstrated that [Ca2+]i oscillations result when these cells are simultaneously depolarized and stimulated with a hormone linked to phosphoinositide breakdown. Further evidence is now presented that such oscillations are linked to fluctuations in the concentration of IP3 and the Ca2+ content of an IP3-sensitive Ca2+ store. [Ca2+]i oscillations can also be generated in REF52 cells either by direct stimulation of G-proteins with GTP gamma S or AlF4- or by destabilizing the membrane potential and opening voltage-dependent calcium channels. This report compares the different types of oscillations and their mechanisms.

The effects of inositol trisphosphates and inositol tetrakisphosphate on Ca2+ release and Cl- current pattern in the Xenopus laevis oocyte

We report that Ins(1,3,4,5)P4 releases calcium from intracellular stores of intact Xenopus laevis oocytes, as indicated by two different techniques, Ca2(+)-sensitive microelectrodes and a fura-2 imaging system. Ins(1,3,4,5)P4 releases only 20% as much Ca2+ as the same amount of Ins(1,4,5)P3. This effect is not due to the conversion of the injected Ins(1,3,4,5)P4 to Ins(1,4,5)P3, which is known to release Ca2+, because the amount of [3H]Ins(1,3,4,5)P4 that is converted to Ins(1,4,5)P3 is extremely small, as determined using HPLC. Examination of the different current patterns induced by Ins(1,4,5)P3 and Ins(1,3,4,5)P4, when injected into voltage-clamped oocytes, provided further evidence that the Ins(1,3,4,5)P4 was not being converted back to Ins(1,4,5)P3. We investigated the effects of four compounds, three inositol trisphosphates (Ins(1,4,5)P3, Ins(2,4,5)P3, and Ins(1,3,4)P3), and Ins(1,3,4,5)P4, on Cl- current conductance in order to examine (1) the possible role of Ins(1,3,4,5)P4 in cell activation and (2) the relationships between intracellular Ca2+ and the activation of Cl- currents. Immature stage VI Xenopus laevis oocytes were voltage-clamped and injected with Ins(1,4,5)P3, Ins(2,4,5)P3, and Ins(1,3,4)P3. Ins(1,4,5)P3 and Ins(2,4,5)P3 triggered Ca2(+)-dependent Cl- currents, but Ins(1,3,4)P3 did not trigger currents nor did it release intracellular Ca2+. Ins(2,4,5)P3 was fourfold less effective at inducing the immediate Cl- current pulse than Ins(1,4,5)P3. The Cl- current pattern was quite dependent on the amount of Ins(1,4,5)P3 injected into the oocyte. Low amounts of Ins(1,4,5)P3 triggered only an immediate single Cl- current pulse, whereas large amounts triggered the immediate single pulse, followed by a quiescent period, followed by oscillating Cl- currents. In contrast to the response of Ins(1,4,5)P3, injection of Ins(1,3,4,5)P4 triggered only oscillating Cl- currents whose magnitude, but not pattern, was dependent on the amount injected into the cell. The currents generated by Ins(1,3,4,5)P4 resemble the oscillating Cl- currents triggered by large amounts of Ins(1,4,5)P3 and Ins(2,4,5)P3. Ins(1,3,4,5)P4, unlike Ins(1,4,5)P3 and Ins(2,4,5)P3, rarely caused an immediate Cl- current pulse, but caused an immediate release of calcium. Therefore, we suggest that the oscillating currents are only indirectly dependent on calcium. These [Ca2+]i and conductance measurements suggest that both Ins(1,4,5)P3 and Ins(1,3,4,5)P4 have roles in intracellular Ca2+ regulation.

Generation of calcium oscillations in fibroblasts by positive feedback between calcium and IP3

A wide variety of nonexcitable cells generate repetitive transient increases in cytosolic calcium ion concentration ([Ca2+]i) when stimulated with agonists that engage the phosphoinositide signalling pathway. Current theories regarding the mechanisms of oscillation disagree on whether Ca2+ inhibits or stimulates its own release from internal stores and whether inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DG) also undergo oscillations linked to the Ca2+ spikes. In this study, Ca2+ was found to stimulate its own release in REF52 fibroblasts primed by mitogens plus depolarization. However, unlike Ca2+ release in muscle and nerve cells, this amplification was insensitive to caffeine or ryanodine and required hormone receptor occupancy and functional IP3 receptors. Oscillations in [Ca2+]i were accompanied by oscillations in IP3 concentration but did not require functional protein kinase C. Therefore, the dominant feedback mechanism in this cell type appears to be Ca2+ stimulation of phospholipase C once this enzyme has been activated by hormone receptors.

Active involvement of Ca2+ in mitotic progression of Swiss 3T3 fibroblasts

Global Ca2+ transients have been observed to precede nuclear envelope breakdown and the onset of anaphase in Swiss 3T3 fibroblasts in 8% (vol/vol) FBS. The occurrence of these Ca2+ transients was dependent on intracellular stores. These Ca2+ transients could be (a) abolished by serum removal without halting mitosis, and (b) eliminated by increasing intracellular Ca2+ buffering capacity through loading the cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) buffer, via the tetra(acetoxymethyl) ester, without hindering the transition into anaphase. Microinjection of sufficient concentrations of BAPTA buffer could block nuclear envelope breakdown. Pulses of Ca2+ generated by flash photolysis of intracellularly trapped nitr-5, a "caged" Ca2+, could precipitate precocious nuclear envelope breakdown in prophase cells. In metaphase cells, photochemically generated Ca2+ pulses could cause changes in the appearance of the chromosomes, but the length of time required for cells to make the transition from metaphase to anaphase remained essentially unchanged regardless of whether a Ca2+ pulse was photoreleased during metaphase. The results from these photorelease experiments were not dependent on the presence of serum in the medium. Discharging intracellular Ca2+ stores with ionomycin in the presence of 1.8 mM extracellular Ca2+ doubled the time for cells to pass from late metaphase into anaphase, whereas severe Ca2+ deprivation by treatment with ionomycin in EGTA-containing medium halted mitosis. Our results collectively indicate that Ca2+ is actively involved in nuclear envelope breakdown, but Ca2+ signals are likely unnecessary for the metaphase-anaphase transition in Swiss 3T3 fibroblasts. Additional studies of intracellular Ca2+ concentrations in mitotic REF52 and PtK1 cells revealed that Ca2+ transients are not observed at all mitotic stages in all cells. The absence of observable global Ca2+ transients, where calcium buffers can block and pulses of Ca2+ can advance mitotic stages, may imply that the relevant Ca2+ movements are too local to be detected.

The molecular and stereochemical structures of photoproducts generated by UV-irradiation of 4'-hydroxymethyl-4,5',8'-trimethylpsoralen in aqueous solution

UV irradiation of 4'-hydroxymethyl-4,5',8-trimethyl psoralen (HMT) in aqueous solution yields three major photoproducts. We have isolated and characterized (1) a cyclobutane-bridged dimer in which a cis-syn linkage occurs between the furan end of one HMT moiety and the pyrone end of the other; (2) a cyclobutane-bridged dimer wherein both HMT moieties are linked at their pyrone ends with probable cis-syn configuration; and (3) an isomer of HMT for which we have proposed a structure in which the furan and pyrone ring oxygens assume a para orientation via photoisomerization.

Imaging and manipulation of cytosolic ions and messengers during cell activation

Optical methods have recently become available for continuously imaging the free concentrations of important ions and second messengers such as calcium, sodium and hydrogen inside living cells. These ion levels are found to undergo remarkable changes upon stimulation of quiescent cells with growth factors known to stimulate phosphoinositide breakdown. In serum-starved REF-52 fibroblasts, growth factors such as serum, vasopressin, or PDGF (platelet-derived growth factor) cause intracellular [Na+] to increase from about 4 mM to 8 mM. If mitogen treatment is combined with pharmacological depolarization of the membrane potential, repetitive [Ca2+]i spikes result in these rat fibroblasts. The mechanism of this oscillation has been investigated by light-flash release of intracellular messengers such as inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), Ca2+, and diacylglycerol, as well as more traditional biochemical techniques. The key feedback pathway appears to be Ca2(+)-stimulation of phospholipase C production of Ins(1,4,5)P3.

Fluorescence ratio imaging of cytosolic free Na+ in individual fibroblasts and lymphocytes

New fluorescent Na+ indicators, SBFI (short for sodium-binding benzofuran isophthalate) and SBFP (short for sodium-binding benzofuran phthalate) (Minta, A., and Tsien, R. Y. (1989) J. Biol. Chem. 264, 19449-19457), were tested in Jurkat tumor lymphocytes and in REF52 rat embryo fibroblasts. Both dyes could be introduced by direct microinjection. However, when cells were incubated with the tetra(acetoxymethyl) esters of the dyes, only SBFI gave intracellular loading that was reasonably responsive to [Na+]i. Because some compartmentation of the SBFI was visible and because the indicator properties are somewhat affected by cytoplasm, the relationship between intracellular free Na+ [( Na+]i and the 340/385 nm excitation ratio of the indicator was calibrated in situ using poreforming antibiotics to equilibrate cytosolic [Na+] [( Na+]i) with extracellular [Na+]. The excitation ratio was sufficiently sensitive to resolve small changes, less than or equal to 1 mM, in [Na+]i in single cells. Basal [Na+]i values in lymphocytes and serum-starved fibroblasts were 9.4 and 4.2 mM, respectively. As expected, large increases in [Na+]i were elicited by blocking the Na+ pump with ouabain or withdrawal of extracellular K+. Mitogens such as phytohemagglutinin acting on the lymphocytes, or serum or vasopressin in fibroblasts, caused [Na+]i to increase up to 2-fold. In fibroblasts, the rise in [Na+]i was due at least partly to a stimulation of Na+ influx, which was not wholly through the Na+/H+ exchanger. The mitogen-induced increases in [Na+]i and the rate of Na+ influx are consistent with earlier estimates based on measurements of total [Na+] or tracer fluxes. However, the absolute values for free [Na+]i are much lower than previous values for total intracellular Na+, suggesting that much of the latter is bound or sequestered.

Photochemically generated cytosolic calcium pulses and their detection by fluo-3

Fluo-3, one member of a family of new fluorescent Ca2+ indicators excitable at wavelengths in the visible (Minta, A., Kao, J. P. Y., and Tsien, R. Y. (1989) J. Biol. Chem. 264, 8171-8178), has been tested in living cells. We demonstrate that fluo-3 can be loaded into fibroblasts and lymphocytes by incubation with the pentaacetoxymethyl ester of the dye and that the ester is hydrolyzed intracellularly to yield genuine fluo-3 capable of indicating changes in [Ca2+]i induced by agonist stimulation. Fluo-3 can also be microinjected into fibroblasts along with photolabile compounds such as nitr-5 and caged inositol trisphosphate for photorelease experiments. Fluo-3 permits continuous monitoring of [Ca2+]i without interference with use of UV-sensitive caged compounds. A procedure for combined use of ionophore and heavy metal ions in end-of-experiment calibration of fluo-3 intensities to give [Ca2+]i is also described.

Fluorescent indicators for cytosolic calcium based on rhodamine and fluorescein chromophores

A new group of fluorescent indicators with visible excitation and emission wavelengths has been synthesized for measurements of cytosolic free Ca2+. The five compounds, "rhod-1," "rhod-2," "fluo-1," "fluo-2," and "fluo-3" (Figs. 2 and 3), combine the 8-coordinate tetracarboxylate chelating site of 1,2-bis(2-amino-phenoxyethane-N,N,N',N'-tetraacetic acid with a xanthene chromophore to give a rhodamine-like or fluorescein-like fluorophore. Binding of Ca2+ increases the fluorescence by up to 40-fold. The Ca2+ dissociation constants are in the range 0.37-2.3 microM, so that the new indicators should give better resolution of high [Ca2+] levels than previously obtainable with quin-2 or fura-2. The visible excitation wavelengths of the new compounds are more convenient for fluorescence microscopy and flow cytometry than the UV required by previous indicators. However, the new dyes' increase in fluorescence upon binding calcium is not accompanied by a wavelength shift, so they are unsuitable for measurements using ratios at two wavelengths. The most promising dye of this series is fluo-3, whose initial biological testing in fibroblasts is described in the following paper (Kao, J. P. Y., Harootunian, A. T., and Tsien, R. Y. (1989) J. Biol. Chem. 264, 8171-8178).

Ca2+ binding kinetics of fura-2 and azo-1 from temperature-jump relaxation measurements

The Ca2+-binding kinetics of fura-2 and azo-1 were studied using temperature-jump relaxation methods. In 140 mM KCl at 20 degrees C, the association and dissociation rate constants for fura-2 were 6.02 x 10(8) M-1s-1 and 96.7 s-1, respectively. The fura-2 kinetics were insensitive to pH over the range 7.4 to 8.4. Azo-1 was studied in 140 mM KCl, at pH 7.4, at 10 degrees and 20 degrees C. At 10 degrees C, azo-1 exhibited association and dissociation rate constants of 1.43 x 10(8) M-1s-1 and 777.9 s-1, respectively; while at 20 degrees C, the corresponding values were 3.99 x 10(8) M-1s-1 and 1,177 s-1. The kinetic results demonstrate that fura-2 and azo-1 are well suited to monitoring rapid changes in intracellular [Ca2+].