Air-liquid interface cultivation of Navicula incerta using hollow fiber membranes.

Microalgae cultivation in open ponds requires a large footprint, while most photobioreactors need improvement in the ratio of surface to volume and energy consumption. In this study, polyethersulfone (PES) and poly(vinylidene fluoride) (PVDF) hollow fiber membranes with a large surface area were rearranged into open-ended and dead-ended configurations to improve the air-liquid interface cultivation of Navicula incerta. N. incerta were successfully grown on the porous membrane surface with the nutrients circulating inside the lumen. Fourier-transform infrared spectra showed the accumulation of polysaccharides, proteins and humic acids. Hydrophilic polysaccharides reduced water contact angles on PES and PVDF membranes to 37.2 ± 2.6° and 55.7 ± 3.3°, respectively. However, the porosity of PES (80.1 ± 1.1%) and PVDF (61.3 ± 4.5%) membranes were not significantly affected even after cultivation and harvesting of N. incerta. Scanning electron images further confirmed that N. incerta, cell debris and extracellular organic matter accumulated on the membrane. With large pores and a hydrophobic surface, PVDF hollow fiber membranes offered a greater improvement in N. incerta cell growth rate compared to PES hollow fiber membranes despite using different configurations. In the dead-ended configuration, they even attained the greatest improvement in N. incerta growth rate, up to 54.0%. However, PES hollow fiber membranes only achieved improvement in harvesting efficiency within the range of 18.7-38.0% due to weak cell adhesion. PVDF hollow fiber membranes significantly promoted the growth of microalgae N. incerta through the air-liquid interface system, leading to potential applications in wastewater treatment.

Recent advances of natural biopolymeric culture scaffold: synthesis and modification.

Traditionally existing 2D culture scaffold has been inappropriately validated due to the failure in generating the precise therapeutic response. Therefore, this leads to the fabrication of 3D culture scaffold resolving the limitations in the in vivo environment. In recent years, tissue engineering played an important role in the field of bio-medical engineering. Biopolymer material, a novel natural material with excellent properties of nontoxic and biodegradable merits can be served as culture scaffold. This review summarizes the modifications of natural biopolymeric culture scaffold with different crosslinkers and their application. In addition, this review provides the recent progress of natural biopolymeric culture scaffold mainly focusing on their properties, synthesizing and modification and application.

Stability evaluation and formula optimization of cellulose-based scaffold for the air-liquid interface cultivation of Navicula incerta.

Culture scaffolds allow microalgae cultivation with minimum water requirement using the air-liquid interface approach. However, the stability of cellulose-based scaffolds in microalgae cultivation remains questionable. In this study, the stability of regenerated cellulose culture scaffolds was enhanced by adjusting TiO2 loading and casting gap. The membrane scaffolds were synthesized using cellulose dissolved in NaOH/urea aqueous solution with various loading of TiO2 nanoparticles. The TiO2 nanoparticles were embedded into the porous membrane scaffolds as proven by Fourier transform infrared spectra, scanning electron microscopic images, and energy-dispersive X-ray spectra. Although surface hydrophilicity and porosity were enhanced by increasing TiO2 and casting gap, the scaffold pore size was reduced. Cellulose membrane scaffold with 0.05 wt% of TiO2 concentration and thickness of 100 µm attained the highest percentage of Navicula incerta growth rate, up to 37.4%. The membrane scaffolds remained stable in terms of weight, porosity and pore size even they were immersed in acidic solution, hydrogen peroxide or autoclaved at 121 °C for 15 min. The optimal cellulose membrane scaffold is with TiO2 loading of 0.5 wt% and thickness of 100 µm, resulting in supporting the highest N. incerta growth rate and and exhibits good membrane stability.

A review on the emerging applications of cellulose, cellulose derivatives and nanocellulose in carbon capture.

Carbon capture can be implemented at a large scale only if the CO2 selective materials are abundantly available at low cost. Since the sustainable requirement also elevated, the low-cost and biodegradable cellulosic materials are developed into CO2 selective adsorbent and membranes recently. The applications of cellulose, cellulosic derivatives and nanocellulose as CO2 selective adsorbents and membranes are reviewed here. The fabrication and modification strategies are discussed besides comparing their CO2 separation performance. Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) isolated from cellulose possess a big surface area for mechanical enhancement and a great number of hydroxyl groups for modification. Nanocellulose aerogels with the large surface area were chemically modified to improve their selectivity towards CO2. Even with the reduction of surface area, amino-functionalized nanocellulose aerogels exhibited the satisfactory chemisorption of CO2 with a capacity of more than 2 mmol/g was recorded. Inorganic fillers such as silica, zeolite and MOFs were further incorporated into nanocellulose aerogels to enhance the physisorption of CO2 by increasing the surface area. Although CO2 adsorbents developed from cellulose and cellulose derivatives were less reported, their applications as the building blocks of CO2 separation membranes had been long studied. Cellulose acetate membranes were commercialized for CO2 separation, but their separation performance could be further improved with silane or inorganic filler. CNCs and CNFs enhanced the CO2 selectivity and permeance through polyvinyl alcohol coating on membranes, but only CNF membranes incorporated with MOFs were explored so far. Although some of these membranes surpassed the upper-bound of Robeson plot, their stability should be further investigated.

Sustainable cultivation of Navicula incerta using cellulose-based scaffold incorporated with nanoparticles in air-liquid interface cultivation system.

Microalgae cultivation using open cultivation systems requires large area and it is susceptible to contamination as well as weather changes. Meanwhile, the closed systems require large capital investment, and they are susceptible to the build-up of dissolved oxygen. Air-liquid interface culture systems with low water-footprint, but high packing density can be used for microalgae cultivation if low-cost culture scaffolds are available. In this study, cellulose-based scaffolds were synthesized using NaOH/urea aqueous solution as the solvent. Titanium dioxide (TiO2), silica gel and polyethylene glycol 1000 (PEG 1000) nanoparticles were added into the membrane scaffolds to increase the hydrophilicity of nutrient absorbing to support the growth of microalgae. The membrane scaffolds were characterized by FTIR, SEM, contact angle, porosity and porometry. All three nanoparticles additives showed their ability in reducing the contact angle of membrane scaffolds from 63.4 ± 2.3° to a range of 52.6 ± 1.2° to 38.8 ± 1.5° due to the hydrophilic properties of the nanoparticles. The decreasing in pore size when nanoparticles were added did not affect the porosity of membrane scaffolds. Cellulose membrane scaffold with TiO2 showed the highest percentage of microalgae Navicula incerta growth rate of 22.1% because of the antibacterial properties of TiO2 in lowering the risk of cell contamination and enhancing the growth of N. incerta. The results exhibited that cellulose-based scaffold with TiO2 added could be an effective support in plant cell culture field.

Fast response of cold ice-rich permafrost in northeast Siberia to a warming climate.

The ice- and organic-rich permafrost of the northeast Siberian Arctic lowlands (NESAL) has been projected to remain stable beyond 2100, even under pessimistic climate warming scenarios. However, the numerical models used for these projections lack processes which induce widespread landscape change termed thermokarst, precluding realistic simulation of permafrost thaw in such ice-rich terrain. Here, we consider thermokarst-inducing processes in a numerical model and show that substantial permafrost degradation, involving widespread landscape collapse, is projected for the NESAL under strong warming (RCP8.5), while thawing is moderated by stabilizing feedbacks under moderate warming (RCP4.5). We estimate that by 2100 thaw-affected carbon could be up to three-fold (twelve-fold) under RCP4.5 (RCP8.5), of what is projected if thermokarst-inducing processes are ignored. Our study provides progress towards robust assessments of the global permafrost carbon-climate feedback by Earth system models, and underlines the importance of mitigating climate change to limit its impacts on permafrost ecosystems.

The genetic architecture of the human cerebral cortex.

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder.

Lake Tauca highstand (Heinrich Stadial 1a) driven by a southward shift of the Bolivian High.

Heinrich events are characterized by worldwide climate modifications. Over the Altiplano endorheic basin (high tropical Andes), the second half of Heinrich Stadial 1 (HS1a) was coeval with the highstand of the giant paleolake Tauca. However, the atmospheric mechanisms underlying this wet event are still unknown at the regional to global scale. We use cosmic-ray exposure ages of glacial landforms to reconstruct the spatial variability in the equilibrium line altitude of the HS1a Altiplano glaciers. By combining glacier and lake modeling, we reconstruct a precipitation map for the HS1a period. Our results show that paleoprecipitation mainly increased along the Eastern Cordillera, whereas the southwestern region of the basin remained relatively dry. This pattern indicates a southward expansion of the easterlies, which is interpreted as being a consequence of a southward shift of the Bolivian High. The results provide a new understanding of atmospheric teleconnections during HS1 and of rainfall redistribution in a changing climate.

Membrane distillation of saline and oily water using nearly superhydrophobic PVDF membrane incorporated with SiO2 nanoparticles.

Fat, oil and grease in wastewater generated from household kitchens, restaurants and food processing plants affect sewer systems, water resources and environment adversely. Hence, membrane distillation of saline and oily water was studied using a nearly superhydrophobic membrane developed in this work. Polyvinylidene fluoride (PVDF) membrane incorporated SiO2 nanoparticles was synthesized via phase inversion with dual baths and modified using hexadecyltrimethoxy silane. The volume ratio of silane to ethanol was varied between 1:200 to 1:25. The membrane characteristics were examined using a goniometer, a porometer, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The PVDF-SiO2 membrane modified using the volume ratio of 1:50 achieved the highest water contact angle of 141.6° and LEP of 2.642 bar. This membrane was further tested in membrane distillation to observe the permeate flux of distilled water, saline solution (1 M NaCl) as well as saline and oily solution (1 M NaCl; 1,000 ppm of palm oil). The modified PVDF/SiO2 showed high permeate flux which is nearly four times of the permeate flux of neat PVDF membrane, but still susceptible of salt and oil fouling as shown in SEM images.

Fouling mitigation in humic acid ultrafiltration using polysulfone/SAPO-34 mixed matrix membrane.

Although ultrafiltration (UF) membranes are applicable in wastewater and water treatment, most UF membranes are hydrophobic and susceptible to severe fouling by natural organic matter. In this work, polysulfone (PSf) membrane was blended with silicaluminophosphate (SAPO) nanoparticles, SAPO-34, to study the effect of SAPO-34 incorporation in humic acid (HA) fouling mitigation. The casting solution was prepared by blending 5-20 wt% of SAPO-34 nanoparticles into the mixture of PSf, 1-methyl-2-pyrrolidinone and polyvinyl alcohol at 75 °C. All membrane samples were then prepared using the phase inversion method. Blending SAPO-34 zeolite into PSf membranes caused augmentation in surface hydrophilicity and pore size, leading to higher water permeation. In the HA filtration test, mixed matrix membranes (MMMs) with SAPO-34 zeolite showed reduced HA fouling initiated from pore blocking. The MMM with 20 wt% SAPO-34 loading exhibited the highest increment of water permeation (83%) and maintained about 75% of permeate flux after 2.5 h. However, the SAPO-34 fillers agglomerated in the PSf matrix and induced macrovoid formation on the membrane surface when excessive zeolite was added.

Potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus for aquaculture.

Aquaculture activities in developing countries have raised deep concern about nutrient pollution, especially excess phosphorus in wastewater, which leads to eutrophication. NF, NF90, NF450 and XLE membranes were studied to forecast the potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus from aquaculture wastewater. Cross-sectional morphology, water contact angle, water permeability and zeta potential of these membranes were first examined. Membrane with higher porosity and greater hydrophilicity showed better permeability. Membrane samples also commonly exhibited high zeta potential value in the polyphosphate-rich solution. All the selected membranes removed more than 90% of polyphosphate from the concentrated feed (75 mg/L) at 12 bar. The separation performance of XLE membrane was well maintained at 94.6% even at low pressure. At low feed concentration, more than 70.0% of phosphorus rejection was achieved using XLE membrane. The formation of intermolecular bonds between polyphosphate and the acquired membranes probably had improved the removal of polyphosphate at high feed concentration. XLE membrane was further tested and its rejection of polyphosphate reduced with the decline of pH and the addition of ammonium nitrate.

Phosphorus removal using nanofiltration membranes.

A high concentration of phosphorus in wastewater may lead to excessive algae growth and deoxygenation of the water. In this work, nanofiltration (NF) of phosphorus-rich solutions is studied in order to investigate its potential in removing and recycling phosphorus. Wastewater samples from a pulp and paper plant were first analyzed. Commercial membranes (DK5, MPF34, NF90, NF270, NF200) were characterized and tested in permeability and phosphorus removal experiments. NF90 membranes offer the highest rejection of phosphorus; a rejection of more than 70% phosphorus was achieved for a feed containing 2.5 g/L of phosphorus at a pH <2. Additionally, NF90, NF200 and NF270 membranes show higher permeability than DK5 and MPF34 membranes. The separation performance of NF90 is slightly affected by phosphorus concentration and pressure, which may be due to concentration polarization and fouling. By adjusting the pH to 2 or adding sulfuric acid, the separation performance of NF90 was improved in removing phosphorus. However, the presence of acetic acid significantly impairs the rejection of phosphorus.

Synthesis and characterization of polymeric V2O5/AlO(OH) with nanopores on alumina support.

Polymeric vanadium pentoxide gel was formed via the reaction of V2O5 powder with hydrogen peroxide. The polymeric vanadium pentoxide gel was then dispersed in alumina gel. Different vanadium loading composites were coated on alumina support and calcined at 500 degrees C for 1 hr. These composite layers were characterized using TGA, FT-IR, XRD, SEM, and Autosorb. It was found that the lamellar structure of polymerized vanadium pentoxide was retained in the inorganic matrix. Crystalline alumina in gamma phase was formed after calcinations. However, the vanadium-alumina mixed oxides are lack of the well defined PXRD peaks for polycrystalline V2O5. This is possibly because the vanadia species are highly dispersed in the alumina matrix or the vanadia species are dispersed as crystalline which is smaller than 4 nm. In addition, the imbedded polymeric vanadium oxide improved the specific area and average pore diameter of the composite layer.

Underphosphorylated BAD interacts with diverse antiapoptotic Bcl-2 family proteins to regulate apoptosis.

Survival factors activate kinases which, in turn, phosphorylate the proapoptotic Bcl-xl/Bcl-2-associated death promoter homolog (BAD) protein at key serine residues. Phosphorylated BAD interacts with 14-3-3 proteins, and overexpression of 14-3-3 attenuates BAD-mediated apoptosis. Although BAD is known to interact with Bcl-2, Bcl-w, and Bcl-xL, the exact relationship between BAD and anti- or proapoptotic Bcl-2 proteins has not been analyzed systematically. Using the yeast two-hybrid protein interaction assay, we found that BAD interacted negligibly with proapoptotic Bcl-2 proteins. Even though wild type BAD only interacted with selected numbers of antiapoptotic proteins, underphosphorylated mutant BAD interacted with all antiapoptotic Bcl-2 proteins tested (Bcl-2, Bcl-w, Bcl-xL, Bfl-1/A1, Mcl-1, Ced-9, and BHRF-1). Using nonphosphorylated recombinant BAD expressed in bacteria, direct interactions between BAD and diverse antiapoptotic Bcl-2 members were also observed. Furthermore, apoptosis induced by BAD was blocked by coexpression with Bcl-2, Bcl-w, and Bfl-1. Comparison of BAD orthologs from zebrafish to human indicated the conservation of a 14-3-3 binding site and the BH3 domain during evolution. Thus, highly conserved BAD interacts with diverse antiapoptotic Bcl-2 members to regulate apoptosis.

DNA array analysis of changes in preovulatory gene expression in the rat ovary.

During the periovulatory period, the mammalian ovary is the site of dramatic functional and structural changes, leading to oocyte maturation, follicle rupture, and corpus luteum formation. To a large extent, these processes result from changes in the transcriptome of various ovarian cell types. To develop a broader view of periovulatory changes in gene expression in the ovary and to identify further genes involved in periovulatory events, we used the recently developed DNA array technology. Immature female eCG-primed rats were killed either immediately before or 6 h after ovulation induction with hCG. Total ovarian RNA was isolated and used to prepare radiolabeled cDNA probes, which were hybridized to DNA arrays representing approximately 600 rat genes. Quantitative analysis identified a multitude of regulated gene messages, including several genes involved in extracellular matrix degradation and lipid/steroid metabolism previously reported to be induced by hCG. This screening also identified a group of candidate genes whose ovarian expression and gonadotropin regulation was hitherto unknown. The induction of three of these genes, encoding cutaneous fatty acid-binding protein, the interleukin-4 receptor alpha chain, and prepronociceptin, was confirmed and further characterized by Northern blot analysis. In addition, in situ hybridization analysis showed that hCG administration resulted in exclusive or predominant expression of all three genes in theca cells. These results demonstrate that DNA arrays can be used to identify genes regulated during the periovulatory period, thus contributing to a more detailed understanding of the molecular mechanisms of ovulation.

The Ovarian Kaleidoscope database: an online resource for the ovarian research community.

The Ovarian Kaleidoscope database (OKdb) is a collaborative online resource for scientists investigating the ovary. It provides information regarding the biological function, expression pattern, and regulation of genes expressed in the ovary as well as for the phenotypes associated with their mutation. In addition, the records in the OKdb are linked to other sites offering online information about biomedical publications, nucleotide and amino acid sequences, and human genes and genetic disorders. A powerful search tool allows the retrieval of records for specific genes and gene products based on their properties at the molecular, cellular, ovarian, or organism level. Researchers working on particular aspects of ovarian physiology can submit information into the database through a simple web-based form and instantly update their records as additional data become available. Because of this approach, the OKdb website could serve as a tool with which to navigate through the rapidly expanding amount of information about the expression and function of individual genes in the ovary and could also enhance communication within the ovarian research community. Moreover, the design of the OKdb could serve as a model for the development of other online databases of tissue-specific gene expression and function. The OKdb can be accessed at http://ovary.stanford.edu/.

MCL-1S, a splicing variant of the antiapoptotic BCL-2 family member MCL-1, encodes a proapoptotic protein possessing only the BH3 domain.

MCL-1 (myeloid cell leukemia-1) is an antiapoptotic BCL-2 family protein discovered as an early induction gene during myeloblastic leukemia cell differentiation. This survival protein has the BCL-2 homology (BH) domains 1, 2, and 3 and a C-terminal transmembrane region. We identified a short splicing variant of the MCL-1 mRNA in the human placenta encoding a protein, termed MCL-1 short (MCL-1S), with an altered C terminus as compared with the full-length MCL-1 long (MCL-1L), leading to the loss of BH1, BH2, and the transmembrane domains. Analysis of the human MCL-1 gene indicated that MCL-1S results from the splicing out of exon 2 during mRNA processing. MCL-1S, unlike MCL-1L, does not interact with diverse proapoptotic BCL-2-related proteins in the yeast two-hybrid system. In contrast, MCL-1S dimerizes with MCL-1L in the yeast assay and coprecipitates with MCL-1L in transfected mammalian cells. Overexpression of MCL-1S induces apoptosis in transfected Chinese hamster ovary cells, and the MCL-1S action was antagonized by the antiapoptotic MCL-1L. Thus, the naturally occurring MCL-1S variant represents a new proapoptotic BH3 domain-only protein capable of dimerizing with the antiapoptotic MCL-1L. The fate of MCL-1-expressing cells could be regulated through alternative splicing mechanisms and interactions of the resulting anti- and proapoptotic gene products.

Characterization of the antiapoptotic Bcl-2 family member myeloid cell leukemia-1 (Mcl-1) and the stimulation of its message by gonadotropins in the rat ovary.

The majority of ovarian follicles undergo atresia mediated by apoptosis. Bcl-2-related proteins act as regulators of apoptosis via the formation of dimers with proteins inside and outside the Bcl-2 family. Previous studies have identified BAD as a proapoptotic Bcl-2 family member expressed in the ovary. It is known that BAD phosphorylation induced by survival factors leads to its preferential binding to 14-3-3 and suppression of the death-inducing function of BAD. To identify ovarian binding partners for hypophosphorylated BAD, we performed a yeast two-hybrid screening of a rat ovary complementary DNA library using as bait a mutant BAD incapable of binding to 14-3-3. Screening of yeast transformants yielded positive clones encoding the rat ortholog of Mcl-1 (myeloid cell leukemia-1), an antiapoptotic Bcl-2 protein. Amino acid sequence analysis revealed that rat and human Mcl-1 showed a complete conservation of the Bcl-2 homology domains BH1, BH2, and BH3. In the yeast two-hybrid system, Mcl-1 binds to the hypophosphorylated mutant of BAD and interacts preferentially with different proapoptotic (Bax, Bak, Bok, Bik, and BOD) compared with antiapoptotic Bcl-2 family members (Bcl-2, Bcl-xL, Bcl-w, Bfl-1, CED-9, and BHRF-1). Northern blot hybridization demonstrated expression of Mcl-1 transcripts of 2.3 and 3.7 kb in the ovary and diverse other rat tissues. In immature rats, PMSG treatment led to a transient increase in the 2.3-kb Mcl-1 transcript, peaking at 6 h after injection and returning to baseline levels after 24 h. Moreover, the same transcript was induced in the PMSG-primed preovulatory rat ovary 6 h after the administration of ovulatory doses of either hCG or FSH. In situ hybridization studies revealed that the gonadotropin stimulation of ovarian Mcl-1 message occurs in both granulosa and thecal cells. In conclusion, rat Mcl-1 was identified as an ovarian BAD-interacting protein and the message for the antiapoptotic Mcl-1 protein was induced after treatment with gonadotropins in granulosa and thecal cells of growing follicles.

DEFT, a novel death effector domain-containing molecule predominantly expressed in testicular germ cells.

Apoptosis is a physiological process by which multicellular organisms eliminate unwanted cells. Death factors such as Fas ligand induce apoptosis by triggering a series of intracellular protein-protein interactions mediated by defined motifs found in the signaling molecules. One of these motifs is the death effector domain (DED), a stretch of about 80 amino acids that is shared by adaptors, regulators, and executors of the death factor pathway. We have identified the human and rat complementary DNAs encoding a novel protein termed DEFT (Death EFfector domain-containing Testicular molecule). The N-terminus of DEFT shows a high degree of homology to the DEDs found in FADD (an adaptor molecule) as well as procaspase-8/FLICE and procaspase-10/Mch4 (executors of the death program). Northern blot hybridization experiments have shown that the DEFT messenger RNA (mRNA) is expressed in a variety of human and rat tissues, with particularly abundant expression in the testis. In situ hybridization analysis further indicated the expression of DEFT mRNA in meiotic male germ cells. In a model of germ cell apoptosis induction, an increase in testis DEFT mRNA was found in immature rats after 2 days of treatment with a GnRH antagonist. Unlike FADD and procaspase-8/FLICE, overexpression of DEFT did not induce apoptosis in Chinese hamster ovary cells. Although cotransfection studies indicated that DEFT is incapable of modulating apoptosis effected by FADD and procaspase-8/FLICE, interactions between DEFT and uncharacterized DED-containing molecules in the testis remain to be studied in the future. In conclusion, we have identified a novel DED-containing protein with high expression in testis germ cells. This protein may be important in the regulation of death factor-induced apoptosis in the testis and other tissues.

K+ channels and the intracellular calcium signal in human melanoma cell proliferation.

K+ channels, membrane voltage, and intracellular free Ca2+ are involved in regulating proliferation in a human melanoma cell line (SK MEL 28). Using patch-clamp techniques, we found an inwardly rectifying K+ channel and a calcium-activated K+ channel. The inwardly rectifying K+ channel was calcium independent, insensitive to charybdotoxin, and carried the major part of the whole-cell current. The K+ channel blockers quinidine, tetraethylammonium chloride and Ba2+ and elevated extracellular K+ caused a dose-dependent membrane depolarization. This depolarization was correlated to an inhibition of cell proliferation. Charybdotoxin affected neither membrane voltage nor proliferation. Basic fibroblast growth factor and fetal calf serum induced a transient peak in intracellular Ca2+ followed by a long-lasting Ca2+ influx. Depolarization by voltage clamp decreased and hyperpolarization increased intracellular Ca2+, illustrating a transmembrane flux of Ca2+ following its electrochemical gradient. We conclude that K+ channel blockers inhibit cell-cycle progression by membrane depolarization. This in turn reduces the driving force for the influx of Ca2+, a messenger in the mitogenic signal cascade of human melanoma cells.