Membrane depolarization in PC-12 cells during hypoxia is regulated by an O2-sensitive K+ current

1996 ◽  
Vol 271 (2) ◽  
pp. C658-C665 ◽  
Author(s):  
W. H. Zhu ◽  
L. Conforti ◽  
M. F. Czyzyk-Krzeska ◽  
D. E. Millhorn
Keyword(s):  
Membrane Potential ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Membrane Depolarization ◽  
Resting Membrane Potential ◽  
Current Clamp ◽  
Pc 12 Cells ◽  
Current Voltage ◽  
K Current

The effects of hypoxia on K+ current (IK), resting membrane potential, and cytosolic free Ca2+ in rat pheochromocytoma (PC-12) cells were studied. Whole cell voltage- and current-clamp experiments were performed to measure IK and membrane potential, respectively. Cytosolic free Ca2+ level was measured using the Ca(2+)-sensitive fluorescent dye fura 2. Depolarizing voltage steps to +50 mV from a holding potential of -90 mV elicited a slowly inactivating, tetraethylammonium chloride-sensitive, and Ca(2+)-insensitive IK that was reversibly inhibited by reduced O2 tension. Graded reduction in PO2 (from 150 to 0 mmHg) induced a graded inhibition of O2-sensitive IK [IK(O2)] up to 46% at 0 mmHg. Moreover, hypoxia induced a 19-mV membrane depolarization and a twofold increase in cytosolic free Ca2+. In Ca(2+)-free condition, inhibition of IK(O2) induced an 8-mV depolarization, suggesting that inhibition of IK(O2) was responsible for initiating depolarization. The effect of reduced PO2 on the current-voltage relationship showed a reduction of outward current and a 14-mV shift in the reversal potential comparable with the amount of depolarization measured in current clamp experiments. Neither Ca(2+)-activated IK nor inwardly rectifying IK are responsible for the hypoxia-induced depolarization. In conclusion, PC-12 cells express an IK(O2), inhibition of which leads to membrane depolarization and increased intracellular Ca2+, making the PC-12 clonal cell line a useful model for studying the molecular and biophysical mechanisms that mediate O2 chemosensitivity.

Characterization of synaptically mediated fast and slow inhibitory processes in piriform cortex in an in vitro slice preparation

1988 ◽  
Vol 59 (5) ◽  
pp. 1352-1376 ◽  
Author(s):  
G. F. Tseng ◽  
L. B. Haberly
Keyword(s):  
Membrane Potential ◽  
Piriform Cortex ◽  
Reversal Potential ◽  
Pyramidal Cells ◽  
Membrane Depolarization ◽  
Resting Membrane Potential ◽  
Excitatory Postsynaptic Potential ◽  
Pentobarbital Sodium ◽  
Postsynaptic Potential ◽  
Conductance Increase

1. Intracellular recordings were obtained from anatomically verified layer II pyramidal cells in slices from rat piriform cortex cut perpendicular to the surface. 2. Responses to afferent and association fiber stimulation at resting membrane potential consisted of a depolarizing potential followed by a late hyperpolarizing potential (LHP). Membrane polarization by current injection revealed two components in the depolarizing potential: an initial excitatory postsynaptic potential (EPSP) followed at brief latency by an inhibitory postsynaptic potential (IPSP) that inverted with membrane depolarization and truncated the duration of the EPSP. 3. The early IPSP displayed the following characteristics suggesting mediation by gamma-aminobutyric acid (GABA) receptors linked to Cl- channels: associated conductance increase, sensitivity to increases in internal Cl- concentration, blockage by picrotoxin and bicuculline, and potentiation by pentobarbital sodium. The reversal potential was in the depolarizing direction with respect to resting membrane potential so that the inhibitory effect was exclusively via current shunting. 4. The LHP had an associated conductance increase and a reversal potential of -90 mV in normal bathing medium that shifted according to Nernst predictions for a K+ potential with changes in external K+ over the range 4.5-8 mM indicating mediation by the opening of K+ channels and ruling out an electrogenic pump origin. 5. Lack of effect of bath-applied 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) or internally applied ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) on the LHP and failure of high amplitude, direct membrane depolarization to evoke a comparable potential, argue against endogenous mediation of the LHP by a Ca2+ activated K+ conductance [gK(Ca)]. However, an apparent endogenously mediated gK(Ca) with a duration much greater than the LHP was observed in a low percent of layer II pyramidal cells. Lack of effect of 8-Br-cAMP also indicates a lack of dependence of the LHP on cAMP. 6. Other characteristics of the LHP that were demonstrated include: a lack of blockage by GABAA receptor antagonists, a probable voltage sensitivity (decrease in amplitude in the depolarizing direction), and an apparent brief onset latency (less than 10 ms) when the early IPSP was blocked by picrotoxin. The LHP was unaffected by pentobarbital sodium when the early IPSP was blocked by picrotoxin. 7. Both the LHP and early IPSP were blocked by low Ca2+/high Mg2+, consistent with disynaptic mediation.(ABSTRACT TRUNCATED AT 400 WORDS)

Ca2+-activated Cl− current in cultured myenteric neurons from murine proximal colon

2003 ◽  
Vol 284 (4) ◽  
pp. C839-C847 ◽  
Author(s):  
Sok Han Kang ◽  
Pieter Vanden Berghe ◽  
Terence K. Smith
Keyword(s):  
Membrane Potential ◽  
Channel Blocker ◽  
Reversal Potential ◽  
Outward Current ◽  
Proximal Colon ◽  
Time Dependent ◽  
Equilibrium Potential ◽  
Resting Membrane Potential ◽  
Myenteric Neurons ◽  
Whole Cell Patch Clamp

Whole cell patch-clamp recordings were made from cultured myenteric neurons taken from murine proximal colon. The micropipette contained Cs+ to remove K+ currents. Depolarization elicited a slowly activating time-dependent outward current ( I tdo), whereas repolarization was followed by a slowly deactivating tail current ( I tail). I tdo and I tail were present in ∼70% of neurons. We identified these currents as Cl− currents ( I Cl), because changing the transmembrane Cl− gradient altered the measured reversal potential ( E rev) of both I tdo and I tail with that for I tailshifted close to the calculated Cl− equilibrium potential ( E Cl). I Cl are Ca2+-activated Cl− current [ I Cl(Ca)] because they were Ca2+dependent. E Cl, which was measured from the E rev of I Cl(Ca) using a gramicidin perforated patch, was −33 mV. This value is more positive than the resting membrane potential (−56.3 ± 2.7 mV), suggesting myenteric neurons accumulate intracellular Cl−. ω-Conotoxin GIVA [0.3 μM; N-type Ca2+ channel blocker] and niflumic acid [10 μM; known I Cl(Ca) blocker], decreased the I Cl(Ca). In conclusion, these neurons have I Cl(Ca) that are activated by Ca2+entry through N-type Ca2+ channels. These currents likely regulate postspike frequency adaptation.

Role of chloride currents in repolarizing rabbit atrial myocytes

1995 ◽  
Vol 268 (5) ◽  
pp. H1992-H2002 ◽  
Author(s):  
Z. Wang ◽  
B. Fermini ◽  
J. Feng ◽  
S. Nattel
Keyword(s):  
Action Potential ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Disulfonic Acid ◽  
Transient Outward Current ◽  
Atrial Myocytes ◽  
Atrial Cells ◽  
K Current

Rabbit atrial cells manifest a prominent transient outward K+ current (Ito1), but this current recovers slowly from inactivation and is unlikely to be important at physiological rates (3-5 Hz). Depolarization of rabbit atrial cells also elicits a transient Ca(2+)-dependent outward Cl- current (Ito2). To compare the relative magnitude of these transient outward currents at various rates, we applied whole cell voltage-clamp techniques to isolated rabbit atrial myocytes. Whereas peak Ito1 exceeded Ito2 at slow rates (0.1 Hz), Ito1 was strongly reduced as rate was increased (by 97 +/- 2%, mean +/- SE, at 4 Hz), while Ito2 was slightly reduced (by 28 +/- 4%, 4 Hz). The reversal potential of transient outward tail currents at 0.07 Hz was -49 +/- 9 mV, while at 2.5 Hz the reversal potential became -18 +/- 7 mV (calculated Cl- reversal potential -18 mV). The addition of the Cl- transport blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 150 microM) or the replacement of external Cl- with methanesulfonate inhibited a large part of the transient outward current elicited by depolarization at 4 Hz. DIDS and Cl- replacement increased action potential duration in both single rabbit atrial cells and multicellular rabbit atrial preparations. We conclude that the Ca(2+)-dependent Cl- current is substantially larger than the transient K+ current at physiological rates in the rabbit and is likely to play a more important role in action potential repolarization than the latter current in this tissue in vivo.

Delayed rectifier K+ current in rabbit atrial myocytes

1995 ◽  
Vol 269 (2) ◽  
pp. H524-H532 ◽  
Author(s):  
K. Muraki ◽  
Y. Imaizumi ◽  
M. Watanabe ◽  
Y. Habuchi ◽  
W. R. Giles
Keyword(s):  
Maximum Amplitude ◽  
Outward Current ◽  
Cell Voltage ◽  
Inward Rectification ◽  
Resting Membrane Potential ◽  
Delayed Rectifier ◽  
Wave Form ◽  
Class Iii ◽  
Atrial Myocytes ◽  
K Current

The role of delayed rectifier K+ current(s) (IK) in rabbit left atrium was examined by applying the whole cell voltage-clamp technique to isolated single myocytes. Right-triangular waveforms, which mimic the shape of atrial action potentials (APs), and selective blockers were used to compare the contribution of IK with other K+ currents to repolarization of the APs. IK measured at 34 degrees C in atrial myocytes was very small; the maximum peak amplitude of the tail current (IK,tail) at -40 mV was approximately 50 pA. The IK,tail was almost abolished in most cells (approximately 80%) by the application of 1 microM E-4031, a class III antiarrhythmic drug. The E-4031-sensitive current recorded with the triangular command wave-form showed strong inward rectification and had a maximum amplitude of approximately 30 pA at -40 mV. Total outward current elicited by triangular command pulses depended strongly on stimulation frequency. The main frequency-dependent component was a Ca(2+)-independent transient K+ current (I(t)). I(t) elicited by triangular pulses at 1 Hz was substantially reduced by 4-aminopyridine (4-AP) at potentials positive to 0 mV but was not changed significantly by 1 microM E-4031; 100 microM E-4031 reduced I(t) by approximately 30%. The shape of the APs which were recorded from a single rabbit atrial cell strongly depended on the pulse frequency. Application of 1 microM E-4031 increased action potential duration (APD) in > 50% of cells examined but had little effect on the resting membrane potential (RMP). Application of 0.1 mM BaCl2 also lengthened APD and reduced RMP by approximately 20 mV.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane currents evoked by histamine in rabbit basilar artery

1997 ◽  
Vol 272 (2) ◽  
pp. H638-H647 ◽  
Author(s):  
M. Kamouchi ◽  
R. Ogata ◽  
M. Fujishima ◽  
Y. Ito ◽  
K. Kitamura
Keyword(s):  
Membrane Potential ◽  
Basilar Artery ◽  
Reversal Potential ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Physiological Salt Solution ◽  
Inward Current ◽  
Inward Currents ◽  
Patch Technique ◽  
Isolated Smooth Muscle Cells

The membrane current evoked by histamine in isolated smooth muscle cells from rabbit basilar artery was investigated using the perforated-patch technique. When 10 microM histamine was applied in the bath at a holding potential of -60 mV, an inward current (79.2 +/- 55.8 pA) was transiently activated. An outward current was additionally evoked by 10 microM histamine when the membrane was held at -40 mV or less negative potentials. The outward but not the inward current was completely blocked by 100 nM charybdotoxin. A higher concentration of histamine (30 microM) failed to produce the inward current (3.4 +/- 4.8 pA) when Cl- concentration in the pipette was reduced. The apparent reversal potential of the inward current induced by histamine in physiological salt solution, in high-tetraethylammonium (TEA+) solution (bath), or in low-Cl- solution (pipette) was -6.3 +/- 4.4, -7.5 +/- 4.9, or -45.8 +/- 8.5 mV, respectively. Niflumic acid (100 microM) reversibly blocked the inward current, which was also blocked by 10 microM pyrilamine but not by 10 microM cimetidine. When histamine was continuously applied in the bath, spontaneous transient inward currents were generated. Removal of external Ca2+ or addition of 1 microM nicardipine or 2 mM caffeine reduced the amplitude of the histamine-induced inward current. These results suggest that histamine induces an inward current via H1 receptors at the resting membrane potential, possibly due to activation of Cl- currents. The Cl- inward current might be generated by elevation of intracellular Ca2+ via histamine receptors. The inward current may also contribute to control of the Ca2+ influx via a change in the membrane potential.

scholarly journals Simultaneous knockout of Slo3 and CatSper1 abolishes all alkalization- and voltage-activated current in mouse spermatozoa

2013 ◽  
Vol 142 (3) ◽  
pp. 305-313 ◽  
Author(s):  
Xu-Hui Zeng ◽  
Betsy Navarro ◽  
Xiao-Ming Xia ◽  
David E. Clapham ◽  
Christopher J. Lingle
Keyword(s):  
Membrane Potential ◽  
Patch Clamp ◽  
Reproductive Tract ◽  
Outward Current ◽  
Female Reproductive Tract ◽  
Resting Membrane Potential ◽  
Patch Clamp Technique ◽  
Mouse Sperm ◽  
Mammalian Sperm ◽  
K Current

During passage through the female reproductive tract, mammalian sperm undergo a maturation process termed capacitation that renders sperm competent to produce fertilization. Capacitation involves a sequence of changes in biochemical and electrical properties, the onset of a hyperactivated swimming behavior, and development of the ability to undergo successful fusion and penetration with an egg. In mouse sperm, the development of hyperactivated motility is dependent on cytosolic alkalization that then results in an increase in cytosolic Ca2+. The elevation of Ca2+ is thought to be primarily driven by the concerted interplay of two alkalization-activated currents, a K+ current (KSPER) composed of pore-forming subunits encoded by the Kcnu1 gene (also termed Slo3) and a Ca2+ current arising from a family of CATSPER subunits. After deletion of any of four CATSPER subunit genes (CATSPER1–4), the major remaining current in mouse sperm is alkalization-activated KSPER current. After genetic deletion of the Slo3 gene, KSPER current is abolished, but there remains a small voltage-activated K+ current hypothesized to reflect monovalent flux through CATSPER. Here, we address two questions. First, does the residual outward K+ current present in the Slo3 −/− sperm arise from CATSPER? Second, can any additional membrane K+ currents be detected in mouse sperm by patch-clamp methods other than CATSPER and KSPER? Here, using mice bred to lack both SLO3 and CATSPER1 subunits, we show conclusively that the voltage-activated outward current present in Slo3 −/− sperm is abolished when CATSPER is also deleted. Any leak currents that may play a role in setting the resting membrane potential in noncapacitated sperm are likely smaller than the pipette leak current and thus cannot be resolved within the limitation of the patch-clamp technique. Together, KSPER and CATSPER appear to be the sole ion channels present in mouse sperm that regulate membrane potential and Ca2+ influx in response to alkalization.

Acetylcholine and caffeine activate Cl- and suppress K+ conductances in human bronchial smooth muscle

1996 ◽  
Vol 270 (5) ◽  
pp. L772-L781 ◽  
Author(s):  
L. J. Janssen
Keyword(s):  
Smooth Muscle ◽  
Reversal Potential ◽  
Outward Current ◽  
Mean Amplitude ◽  
Equilibrium Potential ◽  
Resting Membrane Potential ◽  
Delayed Rectifier ◽  
Positive Direction ◽  
K Current ◽  
K Currents

The conductance changes underlying agonist-evoked depolarization in human airway smooth muscle (ASM) were examined using single ASM cells liberated enzymatically from noncarcinomatous bronchi and studied using patch-clamp techniques. Step commands to potentials at or more positive than the resting membrane potential evoked outward current, which was predominantly delayed rectifier K+ current with some Ca(2+)-dependent K+ current Caffeine (5 mM) evoked depolarization and contraction lasting several minutes. During voltage clamp at -60 mV, caffeine evoked inward current with a latency of approximately equal to 1 s, mean amplitude of 320 +/- 65 pA, and a duration of approximately equal to 5 s (even though agonist application exceeded this duration). With the use of the perforated-path configuration, these responses could be evoked repeatedly at 4-min intervals for up to 30 min; rupture of the membrane and dialysis of the cytosol, however, abrogated the responses to caffeine. The current was outwardly rectifying with mean reversal potential (Vrev) of -31 +/- 4 mV. When K+ conductances were blocked by Ca+, the current-voltage (I-V) relationship was linear (i.e., an outwardly-rectifying component was eliminated) and Vrev was displaced in the positive direction to +2 +/- 1 mV. Changes in the CL- equilibrium potential were accompanied by a displacement of Vrev in a manner predicted by the Nernst equation for a Cl- current. The effects of caffeine were mimicked by acetylcholine; in addition, acetylcholine and caffeine each occluded the response to the other agonist. Spasmogens also caused a prolonged suppression of K+ currents (both Ca(2+)--dependent and delayed rectifier). We conclude that, in human ASM, acetylcholine and caffeine cause a transient activation of Ca(2+)--dependent Cl- current (due to release of internal Ca2+) and prolonged suppression of K+ currents, leading to depolarization and contraction.

Chloride conductance pathways in heart

1991 ◽  
Vol 261 (3) ◽  
pp. C399-C412 ◽  
Author(s):  
J. R. Hume ◽  
R. D. Harvey
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Cardiac Muscle ◽  
Action Potential Duration ◽  
Historical Perspective ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Transient Outward Current ◽  
K Current ◽  
Cl Conductance

Nonelectrogenic movement of Cl- is believed to be responsible for the active accumulation of intracellular Cl- in cardiac muscle. The electro-neutral pathways underlying this nonpassive distribution of Cl- are believed to include Cl(-)-HCO3- exchange, Na(+)-dependent cotransport (operating as Na(+)-Cl- and Na(+)-K(+)-2Cl- cotransport), and K(+)-Cl- cotransport. The electrogenic movement of Cl- in cardiac muscle is particularly interesting from a historical perspective. Until recently, there was some doubt as to whether Cl- carried any current in the heart. Early microelectrode experiments indicated that a Cl- conductance probably played an important role in regulating action potential duration and resting membrane potential. Subsequent voltage-clamp experiments identified a repolarizing, transient outward current that was believed to be conducted by Cl-, yet further investigation suggested that this transient outward current was more likely a K+ current, not a Cl- current. This left some doubt as to whether Cl- played any role in regulating membrane potential in cardiac muscle. More recent studies, however, have identified a highly selective Cl- conductance that is regulated by intracellular adenosine 3',5'-cyclic monophosphate, and it appears that this Cl- current may play an important role in the regulation of action potential duration and resting membrane potential.

scholarly journals Activation of Ca(2+)-dependent K+ current by acetylcholine and histamine in a human gastric epithelial cell line.

1993 ◽  
Vol 102 (4) ◽  
pp. 667-692 ◽  
Author(s):  
E Hamada ◽  
T Nakajima ◽  
S Ota ◽  
A Terano ◽  
M Omata ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Epithelial Cell ◽  
Cell Line ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Induced Response ◽  
Epithelial Cell Line ◽  
Bathing Solution ◽  
Pipette Solution ◽  
K Current

The effects of acetylcholine (ACh) and histamine (His) on the membrane potential and current were examined in JR-1 cells, a mucin-producing epithelial cell line derived from human gastric signet ring cell carcinoma. The tight-seal, whole cell clamp technique was used. The resting membrane potential, the input resistance, and the capacitance of the cells were approximately -12 mV, 1.4 G ohms, and 50 pF, respectively. Under the voltage-clamp condition, no voltage-dependent currents were evoked. ACh or His added to the bathing solution hyperpolarized the membrane by activating a time- and voltage-independent K+ current. The ACh-induced hyperpolarization and K+ current persisted, while the His response desensitized quickly (< 1 min). These effects of ACh and His were mediated predominantly by m3-muscarinic and H1-His receptors, respectively. The K+ current induced by ACh and His was inhibited by charybdotoxin, suggesting that it is a Ca(2+)-activated K+ channel current (IK.Ca). The measurement of intracellular Ca2+ ([Ca2+]i) using Indo-1 revealed that both agents increased [Ca2+]i with similar time courses as they increased IK.Ca. When EGTA in the pipette solution was increased from 0.15 to 10 mM, the induction of IK.Ca by ACh and His was abolished. Thus, both ACh and His activate IK.Ca by increasing [Ca2+]i in JR-1 cells. In the Ca(2+)-free bathing solution (0.15 mM EGTA in the pipette), ACh evoked IK.Ca transiently. Addition of Ca2+ (1.8 mM) to the bath immediately restored the sustained IK.Ca. These results suggest that the ACh response is due to at least two different mechanisms; i.e., the Ca2+ release-related initial transient activation and the Ca2+ influx-related sustained activation of IK.Ca. Probably because of desensitization, the Ca2+ influx-related component of the His response could not be identified. Intracellularly applied inositol 1,4,5-trisphosphate (IP3), with and without inositol 1,3,4,5-tetrakisphosphate (IP4), mimicked the ACh response. IP4 alone did not affect the membrane current. Under the steady effect of IP3 or IP3 plus IP4, neither ACh nor His further evoked IK.Ca. Intracellular application of heparin or of the monoclonal antibody against the IP3 receptor, mAb18A10, inhibited the ACh and His responses in a concentration-dependent fashion. Neomycin, a phospholipase C (PLC) inhibitor, also inhibited the agonist-induced response in a concentration-dependent fashion. Although neither pertussis toxin (PTX) nor N-ethylmaleimide affected the ACh or His activation of IK,Ca, GDP beta S attenuated and GTP gamma S enhanced the agonist response.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of membrane potential by an acetylcholine-activated potassium current in trout atrial myocytes

2007 ◽  
Vol 292 (1) ◽  
pp. R388-R395 ◽  
Author(s):  
Cristina E. Molina ◽  
Hans Gesser ◽  
Anna Llach ◽  
Lluis Tort ◽  
Leif Hove-Madsen
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Membrane Potentials ◽  
Resting Membrane Potential ◽  
Atrial Myocytes ◽  
Atrial Tissue ◽  
Isolated Cardiac Myocytes ◽  
Inwardly Rectifying

Application of the current-clamp technique in rainbow trout atrial myocytes has yielded resting membrane potentials that are incompatible with normal atrial function. To investigate this paradox, we recorded the whole membrane current ( Im) and compared membrane potentials recorded in isolated cardiac myocytes and multicellular preparations. Atrial tissue and ventricular myocytes had stable resting potentials of −87 ± 2 mV and −83.9 ± 0.4 mV, respectively. In contrast, 50 out of 59 atrial myocytes had unstable depolarized membrane potentials that were sensitive to the holding current. We hypothesized that this is at least partly due to a small slope conductance of Im around the resting membrane potential in atrial myocytes. In accordance with this hypothesis, the slope conductance of Im was about sevenfold smaller in atrial than in ventricular myocytes. Interestingly, ACh increased Im at −120 mV from 4.3 pA/pF to 27 pA/pF with an EC50 of 45 nM in atrial myocytes. Moreover, 3 nM ACh increased the slope conductance of Im fourfold, shifted its reversal potential from −78 ± 3 to −84 ± 3 mV, and stabilized the resting membrane potential at −92 ± 4 mV. ACh also shortened the action potential in both atrial myocytes and tissue, and this effect was antagonized by atropine. When applied alone, atropine prolonged the action potential in atrial tissue but had no effect on membrane potential, action potential, or Im in isolated atrial myocytes. This suggests that ACh-mediated activation of an inwardly rectifying K+ current can modulate the membrane potential in the trout atrial myocytes and stabilize the resting membrane potential.

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