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C L Chou

Publications and source records attributed to C L Chou.

At least 37 records · Page 2Linked to original sources
PubMed1998

Electrophysiological and immunocytological demonstration of cell-type specific responses to hypoxia in the adult cat carotid body.

We have recently shown two types of cat carotid body cells based on the oxygen sensitivity of voltage-gated potassium channels. In the present study, we attempted to determine the correlation between cell types (glomus cells, sheath cells, and subtypes of glomus cells) and oxygen sensitivity of potassium channels. Further, changes in membrane potentials in response to hypoxia were also examined. Carotid body cells harvested from adult cats were cultured, and a whole cell patch clamp method was applied to determine the oxygen sensitivity of outward current. The tested cells were identified by Lucifer Yellow in the patch pipette. Glomus cells and sheath cells were immunocytochemically identified using tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP) as markers. The cells whose outward current was inhibited by hypoxia showed TH-immunoreactivity but not GFAP-immunoreactivity. The cells whose outward current was not sensitive to hypoxia were GFAP-positive or TH-negative. One TH-positive cell had oxygen-insensitive outward current. The resting membrane potentials of the cells having oxygen-sensitive outward current were significantly higher (-55+/-3 mV) than those of the cells having oxygen-insensitive outward current (-35+/-2 mV). The former type of cells was depolarized during hypoxia, but not the latter type of cells. These results suggest that most glomus cells of the adult cat carotid body possess oxygen-sensitive potassium channels and are depolarized in response to hypoxia. On the other hand, sheath cells and possibly a small fraction of glomus cells possess oxygen-insensitive potassium channels and their membrane potential is not affected by hypoxia.

Animals↗
PubMed1998

Fourfold reduction of water permeability in inner medullary collecting duct of aquaporin-4 knockout mice.

Aquaporin (AQP)-3 and AQP4 water channels are expressed at the basolateral membrane of mammalian collecting duct epithelium. To determine the contribution of AQP4 to water permeability in the initial inner medullary collecting duct (IMCD), osmotic water permeability (Pf) was compared in isolated perfused IMCD segments from wild-type and AQP4 knockout mice. The AQP4 knockout mice were previously found to have normal gross appearance, survival, growth, and kidney morphology and a mild urinary concentrating defect (T. Ma, B. Yang, A. Gillespie, E. J. Carlson, C. J. Epstein, and A. S. Verkman, J. Clin. Invest. 100: 957-962, 1997). Transepithelial Pf was measured in microdissected IMCDs after 18-48 h of water deprivation and in the presence of 0.1 nM arginine vasopressin (to make basolateral Pf rate limiting). Pf values (37 degrees C; means +/- SE in cm/s x 10(-3)) were 56.0 +/- 8.5 for wild-type mice (n = 5) and 13.1 +/- 3.7 for knockout mice (n = 6) (P < 0.001). Northern blot analysis of kidney showed that transcript expression of AQP1, AQP2, AQP3, and AQP6 were not affected by AQP4 deletion. Immunoblot analysis indicated no differences in protein expression of AQP1, AQP2, or AQP3, and immunoperoxidase showed no differences in staining patterns. Coexpression of AQP3 and AQP4 in Xenopus laevis oocytes showed additive water permeabilities, suggesting that AQP4 deletion does not affect AQP3 function. These results indicate that AQP4 is responsible for the majority of basolateral membrane water movement in IMCD but that its deletion is associated with a very mild defect in urinary concentrating ability.

Animals↗
PubMed1998

Phosphoinositide signaling in rat inner medullary collecting duct.

Previous studies in microdissected rat inner medullary collecting duct (IMCD) segments have demonstrated that carbachol, arginine vasopressin (AVP), and the V2 vasopressin receptor agonist 1-desamino-8-D-arginine vasopressin (DDAVP) induce a similar increase in intracellular Ca2+. The present study tested whether these agents activate the phosphoinositide hydrolysis pathway. In intracellular inositol 1,4,5-trisphosphate (IP3) measurements, we found that IMCD suspensions incubated with AVP or DDAVP (10(-8) M) displayed no measurable increase in IP3, whereas IMCD suspensions incubated with the muscarinic cholinergic agent carbachol (100 microM) induced a significant increase in IP3 production. Similarly, carbachol, but not AVP or DDAVP, induced a significant increase in membrane-associated protein kinase C (PKC) enzyme activity. To test what specific PKC isoforms are activated by carbachol in IMCD, we first characterized the PKC isoforms in IMCD suspensions by immunoblotting using affinity-purified antibodies against different PKC isoforms. We identified one classic PKC isoform (alpha), three novel PKC isoforms (delta, epsilon, eta), and one atypical PKC isoform (zeta) in the IMCD. Carbachol induced a cytosol-to-membrane translocation of the PKC-eta isoform but did not alter the distribution of any other isoform. In contrast, AVP had no effect on the distribution of any PKC isoform tested. These data, taken together, demonstrate that carbachol is an activator of the phosphoinositide hydrolysis pathway in IMCD but do not demonstrate signaling via this pathway in response to AVP or DDAVP. These results suggest that the previously observed AVP-stimulated Ca2+ mobilization in IMCD may be due to a mechanism other than activation of the phosphoinositide hydrolysis pathway.

Animals↗
PubMed1998

Escape from vasopressin-induced antidiuresis: role of vasopressin resistance of the collecting duct.

Previously, we demonstrated that escape from vasopressin-induced antidiuresis ("vasopressin escape") in rats is associated with a large, selective decrease in whole kidney expression of aquaporin-2, the vasopressin-regulated water channel. Here, we show that isolated perfused inner medullary collecting ducts (IMCDs) from vasopressin-escape rats desamino-[D-arginine]vasopressin (DDAVP)/water-loaded have dramatically reduced vasopressin-dependent osmotic water permeabilities [46% of control rats (DDAVP alone)], which coincides with a fall in inner medullary aquaporin-2 protein abundance as measured by immunoblotting in the opposite kidney. Furthermore, we demonstrate in IMCD suspensions that cAMP accumulation in response to DDAVP is substantially reduced in the vasopressin-escape rats both in the presence and absence of the phosphodiesterase inhibitor IBMX. By immunoblotting, we show that the abundance of two proteins important in cAMP generation: the stimulatory heterotrimeric G protein subunit Gs and adenylyl cyclase type VI, do not change. We conclude that vasopressin escape is associated with relative vasopressin resistance of the collecting duct cells manifested by decreased intracellular cAMP levels. The decreased cAMP levels can contribute to the demonstrated decrease in collecting duct water permeability in two ways: 1) by causing a decrease in aquaporin-2 expression and 2) by limiting the acute action of vasopressin to increase collecting duct water permeability.

1-Methyl-3-isobutylxanthine↗
PubMed1998

Heart rate variability as an assessment of acute rejection after heart transplantation.

BACKGROUND: Orthotopic heart transplantation is currently a widely accepted treatment for end-stage heart disease. Early detection and adequate therapy of acute rejection increases the survival rate. Currently, the most reliable technique for the detection of acute cardiac rejection (ACR) is endomyocardial biopsy (EMB), which is an invasive procedure with some intrinsic problems. The purpose of this study was to assess heart rate variability (HRV) as a noninvasive procedure for frequent monitoring of ACR. METHODS: Six consecutive orthotopic cardiac transplant recipients were prospectively recruited into this study. The follow-up periods ranged from seven to 359 days (median; 146 days). A precordial electrocardiograph (ECG) of 288 seconds was recorded at 5:00 PM before the patient underwent EMB. The results from the frequency domain analysis of the ECG signals were evaluated to correlate with the findings from EMB. RESULTS: Of 48 EMBs, 42 (87.5%) showed no evidence of rejection, four showed mild focal ACR (EMB grade 1A), one mild diffuse ACR (1B) and one moderate plurifocal ACR (3A). There was no moderate focal ACR (2), severe diffuse ACR (3B) or severe ACR (4). Correlation between ACR (3A) and a significant increase in HRV with a corresponding 'broad-band' or bell-shaped pattern on the power spectrum was noted. CONCLUSIONS: Our study in consecutive cardiac transplant recipients indicates that the changes in HRV provide clinicians with a new concept for heart transplant monitoring. Further study is needed to verify clinical utility.

Acute Disease↗
PubMed1996

Two types of voltage-gated K channels in carotid body cells of adult cats.

The purpose of this study was to investigate if the oxygen-sensitive K channel is present in the carotid body cells of adult cats, and if all carotid body cells express the oxygen-sensitive K channel. A standard patch-clamp technique with a whole-cell configuration was applied to cultured carotid body cells from adult cats. The cells were continuously perfused with Krebs equilibrated with 5% CO2/air or 5% CO2/argon at room temperature. The results showed that electrophysiologically at least two types of cells existed in cultured cat carotid body cells. One type expressed the oxygen-sensitive K channel and the other expressed the oxygen-insensitive K channel. The oxygen-sensitive K channel was voltage-dependent with a threshold potential of -30 mV. No inactivation was observed during 40 ms of stimulation. The slope of the steady-state current-voltage curve was almost linear in the range from -30 mV to +50 mV. Hypoxia (pO2 = 25 mmHg) reversibly depressed the K current by 22%. The current was inhibited by 4-aminopyridine (10 mM) and tetraethylammonium (4-25 mM), but insensitive to charybdotoxin (100 nM). The oxygen-insensitive K channel showed similar characteristics to that of the oxygen-sensitive K channel in the threshold and the speed of activation, and the shape of I-V curve. The cat is the third species in which the oxygen-sensitive K channel was found in the carotid body. The sensitivity of K channels to oxygen may be a unique feature of chemosensory cells, but the properties of the oxygen-sensitive K channels are different among cats, rats, and rabbits.

Animals↗
PubMed1996

Syntaxin-4 is localized to the apical plasma membrane of rat renal collecting duct cells: possible role in aquaporin-2 trafficking.

To evaluate the possible role of a putative vesicle-targeting protein, syntaxin-4, in vasopressin-regulated trafficking of aquaporin-2 water channel vesicles to the apical plasma membrane of renal collecting duct cells, we have carried out immunoblotting, immunocytochemistry, and reverse transcription (RT)-PCR experiments in rat kidney. Immunochemical studies used an affinity-purified, peptide-directed polyclonal antibody to rat syntaxin-4. Immunoblots using membrane fractions from inner medullary collecting duct (IMCD) cell suspensions revealed a solitary protein of 36 kD, the expected molecular mass of syntaxin-4. This protein was enriched in a plasma membrane-enriched membrane fraction from IMCD cells. Immunoperoxidase immunocytochemistry in 0.85-microm cryosections from rat inner medulla revealed discrete labeling of the apical plasma membrane of IMCD cells. RT-PCR demonstrated the presence of syntaxin-4 mRNA in microdissected IMCD segments, confirmed by direct sequencing of the PCR product. In addition, RT-PCR experiments demonstrated syntaxin-4 mRNA in glomeruli, vasa recta, connecting tubules, and thin descending limbs of Henle's loops. The demonstrated localization of syntaxin-4 in the apical plasma membrane of collecting duct principal cells, coupled with previous demonstration of syntaxin-4's putative cognate receptor VAMP2 in aquaporin-2-containing vesicles, supports the view that these proteins could play a role of aquaporin-2 vesicle targeting to the apical plasma membrane.

Amino Acid Sequence↗
PubMed1996

Ozone-induced vagal reflex modulates airways reactivity in rabbits.

We examined the effects of ozone (O3) on central and peripheral airway reactivity and tracheal transepithelial potential difference (PD) in New Zealand white rabbits. Rabbits were exposed for 7 h to either room temperature-humidified filtered air (n = 7) or 0.2 ppm O3 in humidified room air (n = 5). Tracheal PD was recorded 3 h after exposure. Whole lung resistance (RL) and reactivity were partitioned into their central (RC) and peripheral (RP) components using a retrograde catheter and forced oscillation. Changes in RL, RC, and RP in response to NaCl (0.9%) and ACh (100 mM) aerosol challenges were measured before and after vagotomy. Exposure to O3 decreased tracheal PD from -29 +/- 0.6 mV in air-exposed rabbits to -15 +/- 2 mV in O3-exposed rabbits (p < or = 0.0001). Exposure to O3 did not alter RL, RC, or RP. However, the ACh-induced increase in RL in O3-exposed rabbits (140%) was twice that recorded in the air-exposed group (p < or = 0.01). While changes in RP dominated the whole lung response to ACh in air-exposed rabbits, changes in RC were most prominent in the O3-exposed group. Bilateral vagotomy did not alter airway reactivity in control rabbits but did enhance peripheral lung reactivity in O3-exposed rabbits. We conclude that exposure to 0.2 ppm O3 for 7 h affects tracheal epithelial function in rabbits and increases central airway reactivity via vagal mechanisms without altering baseline RL, RC, or RP.

Acetylcholine↗
PubMed1996

Renal aquaporins.

Aquaporins (AQPs) are a newly recognized family of transmembrane proteins that function as molecular water channels. At least four aquaporins are expressed in the kidney where they mediate rapid water transport across water-permeable epithelia and play critical roles in urinary concentrating and diluting processes. AQP1 is constitutively expressed at extremely high levels in the proximal tubule and descending limb of Henle's loop. AQP2, -3 and -4 are expressed predominantly in the collecting duct system. AQP2 is the predominant water channel in the apical plasma membrane and AQP3 and -4 are found in the basolateral plasma membrane. Short-term regulation of collecting duct water permeability by vasopressin is largely a consequence of regulated trafficking of AQP2-containing vesicles to and from the apical plasma membrane.

Aquaporin 1↗
PubMed1996

Permeability criteria for effective function of passive countercurrent multiplier.

The urine concentrating effect of the mammalian renal inner medulla has been attributed to countercurrent multiplication of a transepithelial osmotic difference arising from passive absorption of NaCl from thin ascending limbs of long loops of Henle. This study assesses, both mathematically and experimentally, whether the permeability criteria for effective function of this passive hypothesis are consistent with transport properties measured in long loops of Henle of chinchilla. Mathematical simulations incorporating loop of Henle transepithelial permeabilities idealized for the passive hypothesis generated a steep inner medullary osmotic gradient, confirming the fundamental feasibility of the passive hypothesis. However, when permeabilities measured in chinchilla were used, no inner medullary gradient was generated. A key parameter in the apparent failure of the passive hypothesis is the long-loop descending limb (LDL) urea permeability, which must be small to prevent significant transepithelial urea flux into inner medullary LDL. Consequently, experiments in isolated perfused thin LDL were conducted to determine whether the urea permeability may be lower under conditions more nearly resembling those in the inner medulla. LDL segments were dissected from 30-70% of the distance along the inner medullary axis of the chinchilla kidney. The factors tested were NaCl concentration (125-400 mM in perfusate and bath), urea concentration (5-500 mM in perfusate and bath), calcium concentration (2-8 mM in perfusate and bath), and protamine concentration (300 micrograms/ml in perfusate). None of these factors significantly altered the measured urea permeability, which exceeded 20 x 10(-5) cm/s for all conditions. Simulation results show that this moderately high urea permeability in LDL is an order of magnitude too high for effective operation of the passive countercurrent multiplier.

Animals↗
PubMed1996

Evidence for dual signaling pathways for V2 vasopressin receptor in rat inner medullary collecting duct.

Previous studies have demonstrated that both the V2-receptor agonist, 1-desamino-8-D-arginine vasopressin (dDAVP), and the V1a-receptor agonist, [Phe2, Orn8]vasotocin (PO-VT), increase intracellular calcium concentration ([Ca2+]i) in the rat inner medullary collecting duct (IMCD). The present studies were done to clarify the receptor subtype(s) responsible for calcium mobilization. Measurements of [Ca2+]i, using fura 2 in microdissected IMCD segments, confirmed that arginine vasopressin (AVP), dDAVP, and PO-VT stimulate an increase in [Ca2+]i and that the response to all three agents could be blocked by the specific V2-receptor antagonist, [d(CH2)5(1),D-Ile2, Ile4, Arg8]vasopressin (II-VP). These results would suggest that all three agents acted through the V2 receptor. Furthermore, we showed that PO-VT increased cAMP production in IMCD suspensions and water permeability in isolated perfused tubules. These responses were also blocked by II-VP, indicating that PO-VT is also a V2 agonist in the IMCD. Finally, we utilized the quantitative reverse transcription-polymerase chain reaction technique of Wiesner (Nucleic Acids Res. 20: 5863-5864, 1992) to evaluate V1a and V2 mRNA levels in rat collecting duct. In terminal IMCD, we estimated > 30 copies/cell for V2 receptor mRNA but less than 1 copy/cell of V1a receptor mRNA, thus there is littler or no V1a mRNA expression in the terminal IMCD. These results suggest that calcium mobilization in response to vasopressin analogues is associated with the V2 receptor and that the V2 receptor is linked to both adenylyl cyclase and calcium mobilization in the rat IMCD.

Animals↗
PubMed1995

Vasopressin increases water permeability of kidney collecting duct by inducing translocation of aquaporin-CD water channels to plasma membrane.

Water excretion by the kidney is regulated by the peptide hormone vasopressin. Vasopressin increases the water permeability of the renal collecting duct cells, allowing more water to be reabsorbed from collecting duct urine to blood. Despite long-standing interest in this process, the mechanism of the water permeability increase has remained undetermined. Recently, a molecular water channel (AQP-CD) has been cloned whose expression appears to be limited to the collecting duct. Previously, we immunolocalized this water channel to the apical plasma membrane (APM) and to intracellular vesicles (IVs) of collecting duct cells. Here, we test the hypothesis that vasopressin increases cellular water permeability by inducing exocytosis of AQP-CD-laden vesicles, transferring water channels from IVs to APM. Rat collecting ducts were perfused in vitro to determine water permeability and subcellular distribution of AQP-CD in the same tubules. The collecting ducts were fixed for immunoelectron microscopy before, during, and after exposure to vasopressin. Vasopressin exposure induced increases in water permeability and the absolute labeling density of AQP-CD in the APM. In parallel, the APM:IV labeling ratio increased. Furthermore, in response to vasopressin withdrawal, AQP-CD labeling density in the APM and the APM:IV labeling ratio decreased in parallel to a measured decrease in osmotic water permeability. We conclude that vasopressin increases the water permeability of collecting duct cells by inducing a reversible translocation of AQP-CD water channels from IVs to the APM.

Animals↗
PubMed1995

Effects of a continuous infusion of dopamine on the ventilatory and carotid body responses to hypoxia in cats.

1. We investigated how a continuous infusion of dopamine (DA; 5 micrograms/kg per min), which is often used clinically, would affect the ventilation and carotid chemoreceptor neural activity in anaesthetized cats. 2. In anaesthetized, spontaneously breathing cats, tidal volume (VT) and respiratory frequency (f) were continuously monitored at five levels of inspired oxygen (PIO2 = 110, 130, 150, 170, 760 mmHg) during Da or saline infusion. VT and f were sampled for 1 min after 3 min exposure to each level of PIO2. Time control study was also performed. 3. DA infusion significantly lowered VT under both normoxia and hypoxia in seven of eight cats. Respiratory frequency was not affected by DA infusion. Depression of ventilation during post-hypoxic hyperoxia was augmented by DA infusion. Chemodenervation abolished the ventilatory response to hypoxia and DA did not further affect the ventilatory response to hypoxia. 4. In a second group of artificially ventilated cats, carotid chemoreceptor neural activity was recorded at five levels of arterial oxygen tension. DA infusion significantly depressed carotid chemoreceptor neural activity during normoxia and hypoxia in six of seven cats. 5. These findings suggest that changes in ventilation during low dosage of DA infusion closely correlate with carotid body neural output. A predominant effect of this dosage of DA (5 micrograms/kg per min) was depression in the ventilatory response to hypoxia due to an inhibition of carotid body neural output.

Anesthesia↗
PubMed1995

Oxytocin as an antidiuretic hormone. I. Concentration dependence of action.

Circulating concentrations of oxytocin increase to 10-40 pM in rats in response to osmotic stimuli, suggesting that oxytocin could play a role in regulation of water balance. The present studies tested whether oxytocin at such concentrations increases osmotic water permeability (Pf) in isolated perfused terminal inner medullary collecting ducts (IMCD). In IMCD segments from Sprague-Dawley rats, 20 pM oxytocin added to the peritubular bath caused a two- to threefold increase in Pf, whereas 200 pM oxytocin increased Pf by five- to sixfold (n = 8, P < 0.01). IMCD from Brattleboro rats, which manifest central diabetes insipidus, exhibited a 2.8-fold increase in Pf in response to 20 pM oxytocin and a 4.7-fold increase in response to 200 pM oxytocin. However, in Brattleboro rats, the response to 20 pM oxytocin was dependent on prior water restriction of the rats. Immunoblotting showed no change in the expression of the aquaporin-CD water channel in Brattleboro rats in response to water restriction. Nevertheless, immunofluorescence studies of inner medullary tissue from Brattleboro rats revealed a marked redistribution of the aquaporin-CD water channels to a predominantly apical and subapical localization in IMCD cells in response to water restriction, similar to the redistribution seen in response to vasopressin. Mathematical modeling studies revealed that the measured increase in Pf in response to oxytocin is sufficient to generate a concentrated urine. We conclude that oxytocin can function physiologically as an antidiuretic hormone, mimicking the short-term action of vasopressin on water permeability, albeit with somewhat lower potency.

Animals↗
PubMed1995

Oxytocin as an antidiuretic hormone. II. Role of V2 vasopressin receptor.

We conducted this study to determine what receptor mediates the effect of oxytocin to increase osmotic water permeability (Pf) in the rat inner medullary collecting duct (IMCD). Reverse transcription-polymerase chain reaction (RT-PCR) experiments demonstrated that mRNA for both the oxytocin receptor and the V2 receptor is present in the rat terminal IMCD. In isolated perfused IMCD segments, we found that the V2 vasopressin receptor antagonist [d(CH2)5(1),D-Ile2,Ile4,Arg8]vasopressin, but not oxytocin receptor antagonists, blocked the hydrosmotic response to 200 pM oxytocin. The selective oxytocin receptor agonist [Thr4,Gly7]oxytocin did not increase water permeability. Oxytocin also increased urea permeability in IMCD segments. Studies in IMCD suspensions showed that oxytocin increases adenosine 3',5'-cyclic monophosphate production in a dose-dependent fashion with a half-maximal (EC50) response at 5.2 nM. The dose-response curves were virtually identical for IMCD suspensions from Sprague-Dawley rats and Brattleboro rats. The oxytocin dose-response curve was displaced to the right of the vasopressin dose-response curve (EC50, 0.44 nM). From these results, we conclude that the V2 receptor mediates the hydrosmotic action of oxytocin in rat IMCD.

Animals↗
PubMed1995

Extracellular nucleotide receptor inhibits AVP-stimulated water permeability in inner medullary collecting duct.

The P2u class of nucleotide receptors is linked to mobilization of intracellular Ca2+ in many cell types, including the renal collecting duct cells. In the present studies, we examined the effects of nucleotides (ATP, UTP, and ADP; 10 microM each) on the arginine vasopressin (AVP, 0.1 nM)-stimulated osmotic water permeability (Pf) in in vitro perfused terminal inner medullary collecting ducts (IMCD) of rat. ATP or UTP, when added to the bath, decreased the AVP-stimulated Pf by approximately 40%. These effects were reversible upon withdrawal of the nucleotides. However, addition of ADP to the bath or sham exchange of the bath had no significant effect on the Pf. Furthermore, ATP did not have any significant effect on the Pf stimulated either by a membrane-permeant, nonhydrolyzable adenosine 3',5'-cyclic monophosphate (cAMP) analogue [8-(4-chlorophenylthio)-cAMP, 0.1 mM] o by forskolin (1 microM). In line with these findings, ATP decreased the AVP-stimulated cAMP levels in IMCD suspensions to approximately 68%. In addition, ATP did not exert an inhibitory effect on the AVP-stimulated Pf in the presence of calphostin C (150 nM), an inhibitor of protein kinase C. These results lead us to conclude the following: 1) agonist occupancy of the putative nucleotide receptor in the terminal IMCD causes an inhibition of AVP-stimulated Pf; and 2) this effect is due to a decrease in cellular cAMP levels, most likely resulting from activation of the phosphoinositide signaling pathway.

Animals↗
PubMed1994

Intron sequences determine the expression of kappa light chain genes.

Alterations in kappa light chain expression were demonstrated to originate from genomic changes in the L-V intron (L-IVS) which changed the splicing pattern of the kappa mRNA. In R15, a mutant of mouse myeloma W3129 which produces no kappa light chain, a 358 bp novel sequence element (R15ns) of unknown origin replaced 19 bases of wild-type L-IVS, both altering the normal splicing pattern and activating a cryptic polyadenylation site. Subclones of R15 which reverted to kappa light chain production contained genomic deletions of R15ns and/or the surrounding intron. These deletions led to partial or full restoration of wild type kappa mRNA levels due to further changes in the pattern of mRNA processing. Two cryptic splice acceptor sites and a polyadenylation signal exist in the L-IVS; a cryptic splice acceptor sequence also exists in V kappa. These cryptic sites can be activated by changing the genomic context. It is thus possible to influence light chain expression without altering either the exon sequences or the known regulatory elements. Alterations in splicing patterns also serve to produce kappa light chains with novel variable region sequences and thereby could contribute to antibody diversity. Surprisingly, in the cell line producing this novel kappa light chain, intact alpha heavy chains were secreted in the absence of an apparent association with light chain. These studies also demonstrate that it is not possible to distinguish functional from non-functional genes solely by sequence analysis and that genes can both be inactivated and activated by changes in intron sequences.

Animals↗