Effect of biochar, zeolite and bentonite feed supplements on egg yield and excreta attributes

Bond Brown Layer (BBL) pullets (n = 200, 18 weeks old) were randomly assigned to 10 dietary treatments involving biochar, zeolite and bentonite at nil, 1%, 2%, and 4% w/w supplementation of commercial layer feed. Each treatment was applied to four cages, with five birds per cage, a total of 20 birds per treatment. Birds were maintained on these diets for 25 weeks. Feed conversion ratio was significantly improved (P = 0.001) with biochar-supplemented feed compared with the control and other treatments. Average egg weight was also significantly improved in the treatment groups compared with the control; however, shell weight, shell breaking strength, shell thickness, shell deformation and shell reflectivity, and internal egg-quality traits of albumen height and Haugh unit were not consistently different (P > 0.05). Yolk colour score was decreased significantly (P = 0.001) with the use of increased rate of additives. Intestinal villi height and crypt depth were increased on amended diets. Egg yield was decreased when birds were placed on a fungal contaminated feed. The feed amendments ameliorated this effect, with the best result achieved on a 2% biochar diet. Improved egg production was also noted under commercial certified organic production conditions trialling 2% biochar feed supplementation compared with the control. Thus, supplementation of feed with biochar, zeolite and bentonite improved production performance traits of egg yield and feed conversion ratio, with these additives potentially acting as detoxifiers or inhibiting growth of microbial pathogens, slowing digestion or altering the gut anatomy and microbiota to improve feed conversion ratio.

Mycorrhizal colonisation of three hybrid papayas (Carica papaya) under mulched and bare ground conditions

The use of straw mulching has been demonstrated to decrease soil loss and to improve soil moisture and soil organic matter content in conjunction with papaya (Carica papaya) cultivation. Mulching may also benefit soil biota. In this study, mulching was demonstrated to significantly (P < 0.05) improve arbuscular mycorrhizal fungal colonisation of papaya roots (by a factor of 2.4), but decreased spore density and species diversity (by a factor of 1.5), compared with cultivation in bare ground. The genera Glomus, Acaulospora, Gigaspora and Sclerocystis dominated in both mulched and bare ground systems. The increased mycorrhizal activity in the mulched treatments was matched by an increase in leaf phosphorus in 1995 but not in 1997.

Functional diversity of chemokines and chemokine receptors in response to viral infection of the central nervous system

Encounters with neurotropic viruses result in varied outcomes ranging from encephalitis, paralytic poliomyelitis or other serious consequences to relatively benign infection. One of the principal factors that control the outcome of infection is the localized tissue response and subsequent immune response directed against the invading toxic agent. It is the role of the immune system to contain and control the spread of virus infection in the central nervous system (CNS), and paradoxically, this response may also be pathologic. Chemokines are potent proinflammatory molecules whose expression within virally infected tissues is often associated with protection and/or pathology which correlates with migration and accumulation of immune cells. Indeed, studies with a neurotropic murine coronavirus, mouse hepatitis virus (MHV), have provided important insight into the functional roles of chemokines and chemokine receptors in participating in various aspects of host defense as well as disease development within the CNS. This chapter will highlight recent discoveries that have provided insight into the diverse biologic roles of chemokines and their receptors in coordinating immune responses following viral infection of the CNS.

NIR model development and robustness in prediction of melon fruit total soluble solids

Near infrared spectroscopy (NIRS) can be used for the on-line, non-invasive assessment of fruit for eating quality attributes such as total soluble solids (TSS). The robustness of multivariate calibration models, based on NIRS in a partial transmittance optical geometry, for the assessment of TSS of intact rockmelons (Cucumis melo) was assessed. The mesocarp TSS was highest around the fruit equator and increased towards the seed cavity. Inner mesocarp TSS levels decreased towards both the proximal and distal ends of the fruit, but more so towards the proximal end. The equatorial region of the fruit was chosen as representative of the fruit for near infrared assessment of TSS. The spectral window for model development was optimised at 695–1045 nm, and the data pre-treatment procedure was optimised to second-derivative absorbance without scatter correction. The ‘global’ modified partial least squares (MPLS) regression modelling procedure of WINISI (ver. 1.04) was found to be superior with respect to root mean squared error of prediction (RMSEP) and bias for model predictions of TSS across seasons, compared with the ‘local’ MPLS regression procedure. Updating of the model with samples selected randomly from the independent validation population demonstrated improvement in both RMSEP and bias with addition of approximately 15 samples.

Assessment of internal quality attributes of mandarin fruit. 2. NIR calibration model robustness

The robustness of multivariate calibration models, based on near infrared spectroscopy, for the assessment of total soluble solids (TSS) and dry matter (DM) of intact mandarin fruit (Citrus reticulata cv. Imperial) was assessed. TSS calibration model performance was validated in terms of prediction of populations of fruit not in the original population (different harvest days from a single tree, different harvest localities, different harvest seasons). Of these, calibration performance was most affected by validation across seasons (signal to noise statistic on root mean squared error of prediction of 3.8, compared with 20 and 13 for locality and harvest day, respectively). Procedures for sample selection from the validation population for addition to the calibration population (‘model updating’) were considered for both TSS and DM models. Random selection from the validation group worked as well as more sophisticated selection procedures, with approximately 20 samples required. Models that were developed using samples at a range of temperatures were robust in validation for TSS and DM.

Assessment of internal quality attributes of mandarin fruit. 1. NIR calibration model development

The utility of near infrared spectroscopy as a non-invasive technique for the assessment of internal eating quality parameters of mandarin fruit (Citrus reticulata cv. Imperial) was assessed. The calibration procedure for the attributes of TSS (total soluble solids) and DM (dry matter) was optimised with respect to a reference sampling technique, scan averaging, spectral window, data pre-treatment (in terms of derivative treatment and scatter correction routine) and regression procedure. The recommended procedure involved sampling of an equatorial position on the fruit with 1 scan per spectrum, and modified partial least squares model development on a 720–950-nm window, pre-treated as first derivative absorbance data (gap size of 4 data points) with standard normal variance and detrend scatter correction. Calibration model performance for the attributes of TSS and DM content was encouraging (typical Rc2 of >0.75 and 0.90, respectively; typical root mean squared standard error of calibration of <0.4 and 0.6%, respectively), whereas that for juiciness and total acidity was unacceptable. The robustness of the TSS and DM calibrations across new populations of fruit is documented in a companion study.

Galactomannan content and composition in Cassia brewsteri seed

Seed galactomannans function as both an energy reserve and a water reservoir in germinating seed of many leguminous plants, and are used commercially as gelling agents, mainly in processed foods. Cassia brewsteri is a leguminous tree endemic to eastern Queensland. The galactomannan content of 40 samples of C. brewsteri seed from throughout the distribution of the species ranged from 28.3 to 39.7% of seed dry weight. The galactomannan content of whole seed was 33.7 ± 0.4% (mean and s.e.m. on a dry weight basis). The mannose : galactose ratio ranged from 4.6 to 6.3 and averaged 5.4 ± 0.1. C. brewsteri gums prepared in a manner analogous to that used in the preparation of commercially available carob gum were tested for gel strength relative to the industrial gelling agents carob gum and Senna tora gum. The break force index (BFI) for the most effective C. brewsteri gum preparation was 107% relative to carob gum and 83% relative to Senna tora gum. On the basis of these biochemical and functional data, C. brewsteri has potential as a source of commercial seed galactomannans.

Ecology and biogeography of Cassia brewsteri: assessment of potential sites for cultivation

Cassia brewsteri (F. Muell.) F. Muell. ex Benth. has been identified as a potential multipurpose agroforestry species, and also as a potential source of seed galactomannans (industrial gums). In this study, the natural and cultivated distributions of C. brewsteri were used as a basis for predicting potential sites for cultivation of the tree, using the climate modelling software ANUCLIM. The natural distribution was determined by compilation of data from herbaria and from field studies. The ecological parameters of natural occurrences were characterised in terms of soil and vegetation types by sampling 113 sites throughout the natural distribution in Queensland (18.583–26.150°S, 144.750–152.750°N). In addition to the natural occurrences, a further 11 sites were identified where the tree has been grown successfully in cultivation. Failures of the tree in agroforestry trials in Thailand may be explained by high temperature as a limiting factor in the distribution of the species. Failures of the species in trials in Australia, Zimbabwe and Malawi could not be attributed to climate or soil conditions at the trial sites, indicating that further research on culture of the tree is required to achieve high survival and growth rates.

Modulation of outward potassium currents in aligned cultures of neonatal rat ventricular myocytes during phorbol ester-induced hypertrophy

Protein kinase C-stimulating phorbol esters induce a strong hypertrophic response when applied in vitro to cardiac ventricular myocytes. The aim of this study was to determine if this in vitro model of hypertrophy is associated with changes in the expression of voltage-gated K(+)channels. Myocytes were isolated from 3--4-day-old neonatal rats and cultured on aligned collagen thin gels. Membrane currents were measured with the use of the whole-cell arrangement of the patch clamp technique and the expression levels of the Kv1.4, Kv4.2 and Kv2.1 alpha subunits quantified using Western blot analysis. Voltage steps positive to -30 mV resulted in the activation of both a transient (I(to)) and a sustained (I(sus)) component of outward K(+)current in the aligned myocytes. Overnight exposure to phorbol 12-myristate 13-acetate (PMA) caused a 55% increase in myocyte size and a three-fold reduction in the peak amplitude of I(to). No differences in the half-maximal voltages required for activation and steady-state inactivation were observed between I(to)measured in control and PMA-treated myocytes. In contrast, PMA treatment resulted in a 62% increase in a tetraethylammonium-sensitive component of I(sus)(TEA-I(sus)) and was associated with the appearance of a slow component of current decay. Expression levels of the Kv1.4 and Kv4.2 alpha subunits were strongly depressed in the hypertrophic myocytes, while the density of the Kv2.1 alpha subunit was enhanced. PMA-induced changes in the Kv alpha subunits were partially prevented through inhibition of the mitogen-activated protein kinase (MAPK) pathway. Thus, PMA-induced hypertrophy of cultured ventricular myocytes is associated with an altered expression of voltage-gated K(+)channels.

Lactoferrin binding to the rat asialoglycoprotein receptor requires the receptor's lectin properties

Lactoferrin binds to rat hepatic lectin 1 (RHL1), the major subunit of the asialoglycoprotein (ASGP) receptor, with high affinity, by a galactose-independent mechanism. To better understand the molecular basis of this novel interaction, we compared the binding of lactoferrin and asialo-orosomucoid (ASOR) to isolated rat hepatocytes and to purified ASGP receptors as a function of pH, Ca(2+) and receptor acylation. Binding of (125)I-lactoferrin and (125)I-ASOR to isolated rat hepatocytes at 4 degrees C decreased sharply at pH<6, following similar titration curves. Binding of (125)I-lactoferrin and (125)I-ASOR to hepatocytes was Ca(2+)-dependent. Binding increased progressively at > or =300 microM CaCl(2), in the presence of 1 mM EDTA. Monensin treatment of hepatocytes, which causes hepatocytes to accumulate inactive ASGP receptors, reduced surface binding of (125)I-lactoferrin and (125)I-ASOR by 46 and 49%, respectively, with only a 16% loss of immunodetectable receptor protein from the cell surface. Finally, deacylation of purified ASGP receptors in vitro with 1 M hydroxylamine abolished receptor lectin activity as reflected by the loss of (125)I-ASOR binding as well as the complete loss of specific (125)I-lactoferrin binding. Treatment with 1 M Tris had no effect on binding of either ligand. We conclude from these data that galactose-independent lactoferrin binding to the ASGP receptor requires the receptor's carbohydrate-recognition domain to be in an active configuration. An active configuration is promoted by neutral pH and Ca(2+), and also requires the receptor subunits to be acylated.

Structural and ionic determinants of 5-nitro-2-(3-phenylprophyl-amino)-benzoic acid block of the CFTR chloride channel

1. The goals of this study were to identify the structural components required for arylaminobenzoate block of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel and to determine the involvement of two positively charged amino acid residues, found within the channel, in drug binding. 2. Wild-type and mutant CFTR chloride channels were expressed in Xenopus oocytes and CFTR currents measured using the two microelectrode voltage clamp. Block of the wild-type CFTR current by 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) occurred in a voltage-dependent manner with preferential inhibition of the inward currents (Kd = 166 microM at -90 mV). 3. Removal of the phenyl ring from the aliphatic chain of NPPB, with the compound 2-butylamino-5-nitrobenzoic acid, caused only a small change in CFTR inhibition (Kd = 243 microM), while addition of an extra phenyl ring at this position (5-nitro-2-(3,3-diphenylpropylamino)-benzoic acid) increased drug potency (Kd = 58 microM). In contrast, removal of the benzoate ring (2-amino-4-phenylbutyric acid) or the 5-nitro group (2-(3-phenylpropylamino)-benzoic acid) of NPPB severely limited drug block of the wild-type channel. 4. NPPB inhibition of CFTR currents in oocytes expressing the mutants K335E and R347E also occurred in a voltage-dependent manner. However, the Kds for NPPB block were increased to 371 and 1573 microM, for the K335E and R347E mutants, respectively. 5. NPPB block of the inward wild-type CFTR current was reduced in the presence of 10 mM of the permeant anion SCN-. 6. These studies present the first step in the development of high affinity probes to the CFTR channel.

Mechanical stimulation regulates voltage-gated potassium currents in cardiac microvascular endothelial cells

Vascular endothelial cells are constantly exposed to mechanical forces resulting from blood flow and transmural pressure. The goal of this study was to determine whether mechanical stimulation alters the properties of endothelial voltage-gated K+ channels. Cardiac microvascular endothelial cells (CMECs) were isolated from rat ventricular muscle and cultured on thin sheets of silastic membranes. Membrane currents were measured with the use of the whole-cell arrangement of the patch-clamp technique in endothelial cells subjected to static stretch for 24 hours and compared with measurements from control, nonstretched cells. Voltage steps positive to -30 mV resulted in the activation of a time-dependent, delayed rectifier K+current (IK) in the endothelial cells. Mechanically induced increases of 97%, 355%, and 106% at +30 mV were measured in the peak amplitude of IK in cells stretched for 24 hours by 5%, 10%, and 15%, respectively. In addition, the half-maximal voltage required for IK activation was shifted from +34 mV in the nonstretched cells to -5 mV in the stretched cells. Although IK in both groups of CMECs was blocked to a similar extent by tetraethylammonium, currents in the stretched endothelial cells displayed an enhanced sensitivity to inhibition by charybdotoxin. Preincubation of the CMECs with either pertussis toxin or phorbol 12-myristate 13-acetate during the 24 hours of cell stretch did not prevent the increase in IK. The application of phorbol 12-myristate 13-acetate and static stretch stimulated the proliferation of CMECs. Stretch-induced regulation of K+ channels may be important to control the resting potential of the endothelium and may contribute to capillary growth during periods of mechanical perturbation.

Legume and opportunity cropping systems in central Queensland. 1. Legume growth, nitrogen fixation, and water use

An experiment, established on a cracking clay (Vertisol) at Emerald, central Queensland, studied the dry matter (DM) production, nitrogen (N) fixation, and water use of several potential ley-legume species over 4 seasons (1994–1997). Four ley legumes (siratro, Macroptilium atropurpureum cv. Siratro; lucerne, Medicago sativa cv. Trifecta; lablab, Lablab purpureus cv. Highworth; and desmanthus, Desmanthus virgatus cv. Marc) were compared with a pulse (mungbean, Vigna radiata cv. Satin), and grain sorghum (Sorghum bicolor) was included as a non-legume control. Overall, the annual legumes lablab (17.5 t/ha) and mungbean (13.4 t/ha) and the perennial siratro (16.2 t/ha) accumulated more DM than the perennials lucerne (9.6 t/ha) and desmanthus (7.1 t/ha). Lucerne produced little DM in its first year, but in later years had similar production to siratro and lablab. Desmanthus produced >4 t/ha of DM in the first year but barely survived during later seasons. Annual legumes grew faster and exhausted soil water more rapidly than the perennials. The perennials were able to extract more water from the soil than the annual legumes and sorghum, but were inefficient at converting small to moderate rainfall events (25–50 mm) into DM production. During the fallow following the growth of lablab and mungbean, nitrate-N in soil increased and was always greater at the time of re-sowing than for the perennial legumes and sorghum. Initially, the 2 annual legumes derived a high proportion (50% to >70%) of their above-ground N from fixation (%Ndfa) but this declined as the experiment progressed to low values (<13%) in the third and fourth years, reflecting increased supply of nitrate from the soil. In contrast, %Ndfa peaked at 72% for siratro and >90% for lucerne, and remained high (25–50%) throughout the experiment. N fixation rates were strongly negatively correlated with soil nitrate. Over the 4 years, siratro fixed 161 kg N/ha, lucerne 120, lablab 119, mungbean 78, and desmanthus 19 based on above-ground biomass. Mungbean had a net negative N balance (–80 kg N/ha) due to N exported in grain.

Histopathology and Within-Plant Distribution of the Phytoplasma Associated with Australian Papaya Dieback

Dieback-affected papaya plants were characterized by a discoloration of the contents of laticifers, while the anatomy of sieve elements was healthy in appearance until the necrotic stages of the disorder were reached. Laticifer discoloration was not always associated with the presence of phytoplasma in affected tissue, as judged by polymerase chain reaction (PCR) using primers based on the 16S rRNA gene and 16S-23S intergenic spacer region. Phytoplasma DNA was detected in a range of plant tissues, including roots, but not in mature leaves which would act as photoassimilate sources. As plants recovered from a dieback period, the extent of the distribution of both laticifer discoloration and phytoplasma DNA decreased. Phytoplasma cells were not observed in transmission electron microscopy studies of mature sieve elements of dieback-affected leaf, stem, or fruit tissue from plants at various stages of symptom expression, although PCR tests indicated the presence of phytoplasma DNA. Membrane-bound structures, similar in shape and size to phytoplasma cells but interpreted as autophagic vesicles or latex vesicles in immature laticifers, were observed within vacuoles of cells in phloem tissue in leaves displaying tissue breakdown in the form of a water-soaked appearance to veins ("X-Y" patterning). In contrast, phytoplasmas were readily observed in papaya leaves displaying symptoms of yellow crinkle. We conclude that phytoplasma cells are present in very low titer in dieback-affected tissues and that, while the plant appears to limit proliferation of the dieback-associated pathogen, this defense strategy is ultimately unsuccessful because it is associated with a rapid decline of the papaya plant.

Epidemiology of Phytoplasma-Associated Papaya Diseases in Queensland, Australia

Three phytoplasma-related diseases of papaya (Carica papaya), dieback, yellow crinkle, and mosaic, are recognized within Australia. Immature leaf material was sampled every week for 8 months from a cohort of 60 female plants, located within a commercial papaya plantation, to determine the minimum time between infection and symptom expression. Phytoplasma DNA was detected using the polymerase chain reaction (PCR) with primers specific for phytoplasmas in general, and for the stolbur group of phytoplasmas. The dieback-associated phytoplasma was detected 1 week prior to (four cases) or the same week (nine cases) as symptom expression, while phytoplasma DNA was detected between 3 and 11 weeks prior to expression of mosaic symptom (six cases). Lateral shoot regrowth on the lower stem of plants which had suffered dieback disease failed to generate stolbur-specific PCR products in 15 cases. A dual infection with dieback and yellow crinkle or mosaic was diagnosed in a further two cases, using restriction fragment length polymorphism digests, and both cases were interpreted as secondary infections by the dieback-associated phytoplasma. Regrowth in three of seven cases of yellow crinkle- and three of nine cases of mosaic-affected plants tested positive for phytoplasma-specific DNA. Ratooning of dieback-affected plants and removal of yellow crinkle- or mosaic-affected plants is suggested for the management of these diseases.

Phylogenetic positions of phytoplasmas associated with dieback, yellow crinkle and mosaic diseases of papaya, and their proposed inclusion in 'Candidatus Phytoplasma australiense' and a new taxon, 'Candidatus Phytoplasma australasia'

DNA extracted from three papaya (Carica papaya L.) plants, individually affected by dieback, yellow crinkle or mosaic diseases, was subjected to PCR using phytoplasma-specific primers to amplify the 16S rRNA gene plus 16S-23S rRNA intergenic spacer region. Near-complete DNA sequences obtained for the three PCR amplimers were subjected to phylogenetic analyses and direct sequence comparison with other phytoplasma 16S rDNA and 16S-23S spacer region DNA sequences. The papaya yellow crinkle (PpYC) and papaya mosaic (PpM) sequences were identical to each other, but distinctly different from the papaya dieback (PpDB) sequence, showing 90.3% identity in the he 16S rDNA and 87.8% identity in the 16S-23S spacer region DNA sequences. A phylogenetic tree based on 16S rDNA sequences was calculated, in which PpYC and PpM are most closely related to the tomato big bud phytoplasma (TBB; 99.7% 16S rDNA sequence identity) from Australia, within subclade iii. This subclade consists of strains only reported occurring in the Southern Asian region and Australia, which indicates an Asian/Australasian origin. PpDB is most closely related to the Phormium yellow leaf phytoplasma from new Zealand (PYL; 99.9% identity) and the Australian grapevine yellows phytoplasma (AGY; 99.7% identity). These three phytoplasma strains form a distinct clade within subclade xii, which also includes the European strains STOL and VK as another distinct clade. The origin of the closely related but geographically separated AGY-like strains and STOL-like strains of subclade xii is unclear. It is proposed that phytoplasma strains PpDB, PYL and AGY be included in the previously described taxon 'Candidatus Phytoplasma australiense', and that PbYC, PpM and TBB be assigned to a new taxon, "Candidatus Phytoplasma australasia'.

Sertoli cell expression of the cystic fibrosis transmembrane conductance regulator

Mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been associated with a number of male reproductive problems, including testis abnormalities and a reduction in germ cell quality and number. To establish at least one site of functional CFTR expression in the testis, we subjected cultured Sertoli cells to analysis of message, protein, and channel activity for CFTR. With reverse transcription-polymerase chain reaction, we obtained evidence for the presence of CFTR RNA when CFTR primers were used with RNA from cultured Sertoli cells. Western analysis performed with both anti-R and anti-C domain CFTR antibodies revealed immunoreactive material in extracts from primary Sertoli cell cultures that seemed consistent with CFTR previously identified in other cells and tissues. This led us to perform more detailed studies using the whole cell arrangement of the patch-clamp technique. Application of the membrane-soluble cAMP analog, 8-chlorophenyl-thio-cAMP, resulted in the activation of a Cl- current that displayed a permeability sequence of Br- > I- > or = Cl- and was blocked by diphenylamine-2-carboxylate and glibenclamide. In addition, a 13-pS conductance Cl- channel was measured in excised membrane patches exposed to the catalytic subunit of protein kinase A. When taken together, our findings of evidence of CFTR message, immunoreactive material that appeared consistent with CFTR, and Cl- channels with properties similar to those reported for CFTR provide strong evidence that Sertoli cells express a functional CFTR-like protein. The presence of CFTR in these cells may be needed to maintain the specific nutritional and fluid balance in the seminiferous tubule that is vital for normal spermatogenesis.

Arylaminobenzoate block of the cardiac cyclic AMP-dependent chloride current

The cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel has been identified in the cardiac muscle of a number of mammalian species, including humans. The goal of this study was to begin quantifying the structural requirements necessary for arylaminobenzoate block of the CFTR channel. The cardiac cAMP-dependent Cl- current (ICl) was measured using the whole-cell arrangement of the patch-clamp technique in guinea pig ventricular myocytes during stimulation of protein kinase A with forskolin. At drug concentrations below the IC50 value for channel block, reduction of ICl by the arylaminobenzoates occurred in a strongly voltage-dependent manner with preferential inhibition of the inward currents. At higher drug concentrations, block of both the inward and outward ICl was observed. Increasing the length of the carbon chain between the benzoate and phenyl rings of the arylaminobenzoates resulted in a marked increase in drug block of the channel, with IC50 values of 47, 17, and 4 microM for 2-benzylamino-5-nitro-benzoic acid, 5-nitro-2-(2-phenylethylamino)-benzoic acid, and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), respectively. Increasing the carbon chain length further with the compound 5-nitro-2-(4-phenylbutylamino)-benzoic acid, caused no additional increase in the potency of drug block (IC50 = 4 microM). Inhibition of ICl by the arylaminobenzoates was modulated by the pH of the external solution; increasing the pH from 7.4 to 10.0 greatly weakened NPPB block, whereas decreasing the pH to 6.4 enhanced block. In addition, block of ICl was observed during intracellular dialysis of NPPB, and this action was not affected by raising the external pH.

Voltage-gated sodium channels in cardiac microvascular endothelial cells

The goal of this study was to determine whether inward Na+ or Ca2+ currents could be measured in cardiac microvascular endothelial cells (CMEC). CMEC were isolated from rat ventricular muscle and studied during days 1-4 in culture. Differential uptake of fluorescently labeled acetylated low-density lipoproteins (LDL) indicated that the primary culture contained > 90% CMEC. Membrane currents were measured with the use of the whole cell arrangement of the patch-clamp technique with a Cs+ internal solution to prevent contamination by outward K+ currents. Voltage steps positive to -30 mV resulted in the activation of a fast, inward Na+ current (INa). In 20 cells examined, the peak inward current measured at 0 mV was 2.1 pA/pF. The half-maximal voltage required for inactivation of INa was -45 mV, and the current recovered from inactivation with a time constant of 10 ms. Inward currents were eliminated by replacement of external sodium with N-methylglucamine and were blocked by both tetrodotoxin (TTX) (dissociation constant = 5 nM) and saxitoxin (50 nM). Stimulation of protein kinase C, through application of phorbol 12,13-dibutyrate, resulted in an increase in the amplitude of INa without any change in the voltage dependence of current activation. Thus the endothelium of cardiac microvessels may be unique in expressing voltage gated, TTX-sensitive Na+ channels.

Effect of chloride channel blockers on the cardiac CFTR chloride and L-type calcium currents

OBJECTIVES

The aim of this study was to determine the effects of Cl- channel blockers on the cardiac cystic fibrosis transmembrane conductance regulator (CFTR) Cl- current (ICl) and the protein kinase A-regulated L-type calcium current (PKA-ICa).

METHODS

Whole-cell ICl and ICa were recorded from isolated guinea pig ventricular myocytes using the patch clamp technique during stimulation of PKA by forskolin (1 or 2 microM).

RESULTS

The inhibitory effects of clofibric acid, p-chlorophenoxy propionic acid, gemfibrozil, diphenylamine-2-carboxylate (DPC), anthracene-9-carboxylate, 4,4'dinitrostilbene-2,2'-disulfonic acid and indanyloxyacetic acid 94 were examined on the two currents. Clofibric acid (1 mM), p-chlorophenoxy propionic acid (1 mM) and gemfibrozil (250 microM) produced an approximate 50% decrease in ICl, but had no effect on the PKA-ICa. Surprisingly, application of DPC (500 microM and 1 mM) and anthracene-9-carboxylate (500 microM) strongly reduced both currents. However, inhibition of the Ca2+ and Cl- channels by DPC could be differentiated in two important ways. First, increasing the pH of the external solution from 7.4 to 10.0 prevented the block of ICl by DPC, but did not attenuate the reduction in the PKA-ICa. Second, DPC inhibited the PKA-ICa in mouse atrial myocytes which lacked ICl. Neither 4,4'dinitrostilbene-2,2'-disulfonic acid (100 microM) nor indanyloxyacetic acid 94 (50 microM) caused any change in either of the guinea pig ventricular currents.

CONCLUSIONS

Drugs such as DPC and anthracene-9-carboxylate which block the cardiac CFTR Cl- channel also inhibit the regulation of the L-type ICa. During beta-adrenergic stimulation, changes produced by these drugs on the cardiac action potential duration will be attributable to inhibition of both the Cl- and Ca2+ currents. Analogues of clofibric acid may serve as selective blockers of the CFTR Cl- channel that can be used to determine the physiological function of ICl in cardiac excitation.

Stimulatory regulation of the large-conductance, calcium-activated potassium channel by G proteins in bovine adrenal chromaffin cells

G proteins regulate the electrical activity of various cells through their actions on membrane ion channels. In the present study, the effect of G proteins was examined on unitary, large conductance (BK), Ca(2+)-activated K+ channels measured in excised, inside-out patches of membrane obtained from cultured bovine adrenal chromaffin cells. Cytoplasmic application of either guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) or AlF-4 to stimulate G proteins resulted in a > 4-fold increase in the open probability of the BK channel measured at +40 mV in the presence of a 1 microM concentration of Ca2+. A similar stimulatory regulation was observed after the addition of an activated, mixed Gi/Go alpha preparation. The increase in the open probability during G protein stimulation was associated with a large reduction in the duration of a long closed state of the channel and could be observed in the presence of a protein kinase inhibitor. The half-maximal voltage required for steady state activation of the BK channel decreased from +63 mV to +48 mV in the presence of GTP gamma S. In addition, the half-maximal Ca2+ concentration required for channel opening was reduced from 11.7 microM in control measurements to 1.3 microM during regulation by GTP gamma S. Thus, G proteins increase the open probability of the chromaffin BK Ca(2+)-activated K+ channel by shifting the voltage dependence of channel gating to more negative potentials and by enhancing the affinity of the channel for Ca2+. Stimulatory regulation may provide a compensatory mechanism for decreasing the action potential duration during secretagogue-mediated exocytosis.

Australian papaya dieback: evidence against the calcium deficiency hypothesis and observations on the significance of laticifer autofluorescence

The cause of the dieback disorder of Carica papaya (papaya, papaw, or pawpaw) is unknown, although it is a severe problem for the Queensland industry. In this study, tlle progression of morphological and anatomical symptoms during a growing season in Yarwun is documented. Most plants which displayed a brown discoloration of the vascular tissue developed external symptoms. The discoloration initiated in the stem zone which supported leaves, and developed acropetally into the stem apex, and basipetally into the trunk and in part of the root system. The discoloration was autofluorescent under blue or ultraviolet light, and was associated with laticifers in xylem and phloem tissue and in ray parenchyma. Laticifer autofluoresence was not observed in calcium-deficient plants, nor in the browning associated with nematode damage, but this symptom was present in association with tissue damage caused by Amblypelta lutescens (Distant) and in plants suffering root rot. Laticifer discoloration may represent a general stress reaction by the plant. Tyloses developed in xylem elements, associated with the wilting of the crown, following development of leaf chlorosis and the bending of the stem tip. Dieback-affected apical tissues were lower in total calcium content than healthy tissues, but were not below an experimentally determined critical concentration. It is suggested that the low calcium content represents a secondary symptom of the disorder. caused by a tylosis-induced decrease in hydraulic conductivity and consequently in calcium transport.

Revegetation of a scalded saline discharge zone in Central Queensland. 2. Water use by vegetation and watertable drawdown

The hydrological effect of Casuarina glauca trees established on a salt pan in East Barmoya, Central Queensland, is described. The sap flow of a single (4-year-old, 5 m tall) tree was logged with the steady-state heat balance technique at about 11 L/day. The watertable adjacent to the tree was depressed by about 130 mm relative to that 10 m from the tree, and demonstrated a diurnal oscillation of about 10 mm, consistent with an evapotranspiration rate of 1 mm/day. Infiltration was rapid in the vicinity of the tree, such -- that the watertable rose quickly (about 10 mm/h) in the vicinity of the tree after rainfall events. An apparent response of the watertable to changes in barometric pressure was also noted. The density of tree planting required to halt dryland salinity on this site was estimated, and a density trial was commenced with the aim of lowering the watertable to enable the re-establishment of pasture communities between the rows in a form of agroforestry.

A calcium-activated potassium channel in growth plate chondrocytes: regulation by protein kinase A

Single channel K+ currents were recorded from inside-out patches of membrane obtained from cultured chicken growth plate chondrocytes. With a symmetrical 140 mM concentration of K+ across the cell membrane, a large conductance (211 pS), outward-rectifying, K+ channel was identified. Opening of this channel was dependent on the presence of internal Ca2+ with half maximal activation of the channel occurring with 3 microM Ca2+. The channel was blocked by internal application of tetraethylammonium (IC50 = 45 mM) and 1 mM Ba2+. Application of the catalytic subunit of protein kinase A to the cytosolic membrane resulted in over a three-fold increase in the open probability for the channel. Thus, growth plate chondrocytes contain a large-conductance, Ca(2+)-activated K+ channel which can be up-regulated during stimulation of protein kinase A.

A G protein-activated K+ current in bovine adrenal chromaffin cells: possible regulatory role in exocytosis

Guanine nucleotide binding proteins (G proteins) act as signal transducers between membrane receptors and ion channels. In the present study, the whole-cell arrangement of the patch clamp technique was used to examine the effect of G proteins on K+ channels in cultured bovine adrenal chromaffin cells. Internal dialysis of chromaffin cells with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) or external application of AIF-4, to stimulate G proteins, resulted in a voltage-dependent increase in the amplitude of the outward K+ currents. The half-maximal voltage required for activation of the currents was shifted by -16 mV in the presence of GTP gamma S. The augmentation in the K+ currents was accompanied by the appearance of a fast component of current activation measured at potentials positive to 0 mV. The GTP gamma S-sensitive current could not be detected when internal K+ was replaced with Cs+ and was reversibly inhibited by tetraethylammonium (IC50, 2 mM). In contrast, the scorpion venom charybdotoxin (50 nM) and the bee venom apamin (250 nM) only slightly reduced the K+ currents during stimulation by GTP gamma S and did not alter the activation kinetics. In addition, the GTP gamma S-sensitive K+ current could be activated in the absence of internal Ca2+ and when the inward Ca2+ current was inhibited with CdCl2. Treatment of the chromaffin cells with fluoride decreased nicotine-evoked secretion of catecholamines in a concentration-dependent manner. Thus, bovine chromaffin cells contain a G protein-stimulated K+ channel that may play a regulatory role in secretagogue-mediated exocytosis.

Properties of a protein kinase C-activated chloride current in guinea pig ventricular myocytes

Cardiac ventricular myocytes from several species, including the guinea pig, possess a cAMP-dependent protein kinase A (PKA)-activated Cl- channel. In the present study, the properties of a protein kinase C (PKC)-activated Cl- current were studied in isolated guinea pig ventricular myocytes using the whole-cell arrangement of the patch-clamp technique. Intracellular dialysis of ventricular cells with PKC resulted in the activation of a large background current that displayed time-independent kinetics. In the presence of 146 mmol/L external Cl- and 71 mmol/L internal Cl-, the reversal potential (Erev) of the background current (-17 +/- 1 mV) was close to that of the Cl- equilibrium potential (-18 mV), and the current versus voltage relation for the current was outward rectifying in shape. When [Cl-]i or [Cl-]o was reduced by substitution of Cl- with aspartic acid, Erev for the background current shifted in a manner expected for a Cl(-)-selective channel. Based on Erev measurements, the permeability sequence for this PKC-activated Cl- channel was determined to be SCN- > I- > Br- congruent to Cl-. The PKC-activated Cl- current was not inhibited by the Cl- channel blocker 4,4'-dinitrostilbene-2,2'-disulfonic acid (100 mumol/L) but could be blocked by anthracene-9-carboxylic acid (1 mmol/L). Activation of the current was abolished in the presence of the PKC inhibitor staurosporine (2.5 mumol/L). Under conditions designed to cause a maximal activation of the Cl- channels by PKC, the addition of forskolin (1 mumol/L) to stimulate PKA caused only a slight further increase in the amplitude of the Cl- current. Thus, PKC activates a Cl- channel in guinea pig ventricular cells with properties similar but not identical to the PKA-activated channel.

Inhibition of heart calcium and chloride currents by sodium iodide. Specific attenuation in cAMP-dependent protein kinase-mediated regulation

The enzymes cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) regulate the activity of cardiac ion channel proteins. In this study the whole-cell arrangement of the patch clamp technique was used to examine the effect of NaI on PKA-stimulated Cl- and Ca2+ channels in isolated guinea pig ventricular myocytes. Cl- currents (ICl) activated either by the beta-adrenergic agonist isoproterenol or the membrane-soluble cAMP analogue, 8-chlorphenylthio (8-CPT) cAMP, were greatly reduced in amplitude after substitution of an external solution containing 140 mM NaCl with a solution containing 140 mM NaI. This reduction was accompanied by a shift of -7 mV in the reversal potential (Erev) for ICl and could be reversed upon return to the NaCl external solution. Inhibition of ICl by NaI occurred in a concentration-dependent manner and was more pronounced for inward ICl (IC50 = 19 mM at -60 mV) than for outward ICl (IC50 = 60 mM at +60 mV). In contrast to ICl activated by PKA, ICl activated by PKC was slightly augmented in the presence of NaI and the Erev was found to shift by -15 mV. Based on these data, the relative permeability of I- to Cl- (PI/PCl) for this channel was calculated to be 1.79. NaI produced no change in the amplitude of inward calcium currents (ICa) recorded under basal conditions, but strongly inhibited ICa augmented by isoproterenol and 8-CPT cAMP, and during dialysis of cells with the catalytic subunit of PKA (CS). The in vitro incorporation of [gamma-32P]ATP into histone IIA and Kemptide, measured in the presence of PKA and cAMP, was not significantly different in assay mixtures containing salts of Cl- and I-. However, the ability of isoproterenol to augment basal ICa in whole-cell experiments was attenuated when experiments were carried out entirely in NaI external solution. Thus, the reduction in ICl and ICa observed in this study may result from a direct effect of I- on the phosphorylation/dephosphorylation of cardiac ion channel proteins or associated regulatory proteins.

Characterization of a delayed rectifier potassium current in chicken growth plate chondrocytes

With the use of the whole cell arrangement of the patch-clamp technique, an outward-directed time-dependent potassium current was identified in cultured chicken growth plate chondrocytes. This delayed rectifier potassium current (IK) activated with a sigmoidal time course during voltage steps to potentials positive to -40 mV. The half-maximal voltage required for current activation was determined to be -8 mV. The reversal potential (Erev) for IK, measured using deactivating tail currents, was -72 mV in the presence of 140 mM internal and 5 mM external [K+] solutions. Changes in external [K+] caused Erev to shift in a manner expected for a potassium-selective channel. In addition, increasing external [K+] from 5 to 50 mM caused the slope conductance of the tail currents to increase twofold. The chondrocyte IK was inhibited by the potassium-channel blocker 4-aminopyridine (4-AP) at concentrations of 0.5-4 mM and by the scorpion venom toxin charybdotoxin (CTX; 10 nM) but was unaffected by 10 mM tetraethylammonium (TEA). Addition of 20 microM ZnCl2 reduced IK in a voltage-dependent manner with the greatest inhibition found to occur at potentials near the threshold for current activation. Reduction of IK by ZnCl2 was accompanied by a slowing in the kinetics of IK activation. On the basis of the gating and pharmacological properties of this current, it is suggested that the chondrocyte channel belongs to a superfamily of K+ channels found in bone and immune system cells. The chondrocyte K+ channel may contribute to the unusually high [K+] found in the extracellular fluid of growth plate cartilage.

Distinct voltage-dependent regulation of a heart-delayed IK by protein kinases A and C

We have investigated the effects of stimulation of adenosine 3',5'-cyclic monophosphate-dependent protein kinase (protein kinase A) and Ca(2+)-diacylglycerol-dependent protein kinase (protein kinase C) on the delayed rectifier K+ current (IK) in guinea pig ventricular cells using a whole cell arrangement of the patch-clamp procedure. Stimulation of either protein kinase C or A resulted in enhanced IK activity. Augmentation of IK observed during stimulation of protein kinase A occurred in a markedly voltage-dependent manner, with the largest increases occurring at potentials near the threshold for IK activation. Enhancement of IK during stimulation of protein kinase C followed a different pattern, with minimal effects of the enzyme near IK threshold. Neither protein kinase A nor C altered the kinetics of IK activation, although both kinases slightly changed the kinetics of deactivation. Both kinases increased IK maximal conductance, but the effects of each kinase on the voltage-dependence of activation differed. Protein kinase A shifted IK activation toward more negative voltages but did not affect the slope of the activation curve. Protein kinase C, in contrast, changed the slope of the IK activation curve, with only a small effect on the half-maximal voltage of activation. These contrasting effects on the voltage dependence of IK activation are consistent with actions of the kinases at distinct sites on or near the IK channel protein.

Activation of a heart chloride current during stimulation of protein kinase C

The whole-cell arrangement of the patch-clamp technique was used to examine the effect of protein kinase C (PKC) stimulation on ion channels in isolated guinea pig ventricular cells. In the presence of appropriate external solutions and drugs to reduce contamination from sodium, calcium, and potassium ion currents, application of phorbol 12-myristate 13-acetate or phorbol 12,13-dibutyrate, to stimulate PKC, activated a time-independent background current. The current-voltage relation for the PKC-activated current was linear over the voltage range of -90 to +60 mV. Alteration of the chloride equilibrium potential, brought about through changes in external and internal Cl- concentrations, shifted the reversal potential for the background current in a manner expected for a Cl- -selective ion channel. The PKC-activated current was reversibly inhibited by the S-(-)-enantiomer of the monocarboxylic acid derivative 8-chlorophenoxyproprionic acid, at a concentration that did not affect Ca2+ or delayed rectifier K+ currents. Dialysis of ventricular cells with partially purified PKC obtained from rat brain resulted in the activation of a large (greater than 1-nA) time-independent background current after addition of external phorbol 12,13-dibutyrate. In the presence of the beta-adrenergic receptor antagonist propranolol, norepinephrine activated a background current with properties similar to those of the PKC-sensitive current. It is concluded that cardiac ventricular cells contain PKC-activated Cl- channels, which may be regulated during alpha-adrenergic stimulation.

Delayed-rectifier potassium channel activity in isolated membrane patches of guinea pig ventricular myocytes

When the patch-clamp technique was used, a slowly activating, time-dependent outward current was identified in both cell-attached and excised membrane patches obtained from guinea pig ventricular myocytes. This macroscopic patch current was present in approximately 50% of patches studied and could be observed both in the presence and absence of unitary single channel activity (i.e., ATP-sensitive K+ channels). The time course of activation of the patch current resembled that of the whole cell delayed-rectifier K+ current (IK) recorded under similar ionic conditions, and the patch current and IK were activated over a similar membrane potential range. The time-dependent patch current could be eliminated when the Nernst potential for K+ equaled that of the pulse voltage. The patch current was inhibited by external addition of the tertiary ammonium compound LY 97241 (50 microM) and was augmented after internal application of the catalytic subunit of adenosine 3',5'-cyclic monophosphate-dependent protein kinase (500 nM). Deactivating tail currents with kinetics similar to those of IK could be recorded to cell-attached and excised patches. Unitary single channel events underlying the time-dependent patch current could not be resolved despite various attempts to increase single channel conductance. Thus our results suggest that a major component of delayed rectification in guinea pig ventricular cells is due to the activity of a high-density, extremely low conductance K+ channel.

Beta-adrenergic modulation of cardiac ion channels. Differential temperature sensitivity of potassium and calcium currents

beta-Adrenergic stimulation of ventricular heart cells results in the enhancement of two important ion currents that regulate the plateau phase of the action potential: the delayed rectifier potassium channel current (IK) and L-type calcium channel current (ICa). The temperature dependence of beta-adrenergic modulation of these two currents was examined in patch-clamped guinea pig ventricular myocytes at various steps in the beta-receptor/cyclic AMP-dependent protein kinase pathway. External applications of isoproterenol and forskolin were used to activate the beta-receptor and the enzyme adenylate cyclase, respectively. Internal dialysis of cyclic 3',5'-adenosine monophosphate (cAMP) or the catalytic subunit of cAMP-dependent protein kinase (CS), as well as the external addition of 8-chlorphenylthio cAMP (CPT-cAMP) was applied to increase intracellular levels of cAMP and CS. Isoproterenol-mediated increases in IK, but not ICa, were found to be very temperature dependent over the range of 20-37 degrees C. At room temperature (20-22 degrees C) isoproterenol produced a large (threefold) enhancement of ICa but had no effect on IK. In contrast, at warmer temperatures (30-37 degrees C) both currents increased in the presence of this agonist and the kinetics of IK were slowed at -30 mV. A similar temperature sensitivity also existed after exposure to forskolin, CPT-cAMP, cAMP, and CS, suggesting that this temperature sensitivity of IK may arise at the channel protein level. Modulation of IK during each of these interventions was accompanied by a slowing in IK kinetics. Thus, regulation of cardiac potassium channels but not calcium channels involves a temperature-dependent step that occurs after activation of the catalytic subunit of cAMP-dependent protein kinase.

Regulation of a heart potassium channel by protein kinase A and C

The enzymes adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase (protein kinase A) and protein kinase C regulate the activity of a diverse group of cellular proteins including membrane ion channel proteins. When protein kinase A was stimulated in cardiac ventricular myocytes with the membrane-soluble cAMP analog 8-chlorphenylthio cAMP (8-CPT cAMP), the amplitude of the delayed-rectifier potassium current (IK) doubled when recorded at 32 degrees C but was not affected at 22 degrees C. In contrast, modulation of the calcium current (ICa) by 8-CPT cAMP was independent of temperature with similar increases in ICa occurring at both temperatures. Stimulation of protein kinase C by phorbol 12,13-dibutyrate also enhanced IK in a temperature-dependent manner but failed to increase ICa at either temperature. Thus, cardiac delayed-rectifier potassium but not calcium channels are regulated by two distinct protein kinases in a similar temperature-dependent fashion.

Regulation of o(2) concentration in soybean nodules observed by in situ spectroscopic measurement of leghemoglobin oxygenation

A fiber optic spectrophotometric system was used to monitor the in vivo oxygenation of leghemoglobin in intact, attached soybean root nodules (Glycine max L. Merr. x USDA 16 Bradyrhizobium japonicum) which were flattened during development by growth in narrow, glass-walled cuvettes. When equilibrated at an external pO(2) of 20 kilopascals, leghemoglobin was 36.6 +/- 5.4% oxygenated, a value estimated to represent an infected cell O(2) concentration of 21.5 nanomolar. Increasing the external pO(2) from 20 to 25 kilopascals caused a rapid increase in leghemoglobin oxygenation, followed by a recovery to the initial level, all within 7.5 minutes. At 25 kilopascals O(2), the rates of H(2) and CO(2) evolution were similar to those at 20 kilopascals. Since respiration had not increased, the results support the proposal that nodules adapt to increased external pO(2) by regulating their resistance to O(2) diffusion.

Action of diltiazem on excitation-contraction coupling in bullfrog skeletal muscle fibers

In this study the calcium antagonist drug diltiazem was found to produce twitch potentiation, lower the mechanical threshold potential and block inward calcium currents in bullfrog skeletal muscle fibers. Under tonic conditions (stimulation either every 1 or 2 min) high concentrations of diltiazem were required to enhance twitch tension (ED50 = 249 microM) and block calcium currents (IC50 = 190 microM). In addition, 100 microM diltiazem lowered the mechanical threshold rheobase potential from -49.3 to -57.0 mV. At higher rates of stimulation, concentrations of diltiazem as low as 1 and 10 microM, which had no tonic action, were found to produce twitch potentiation and calcium channel block, respectively. Onset and washout of tonic and frequency-dependent actions of diltiazem on twitch and current amplitude occurred over a similar time course. It is proposed that the mechanical potentiation, as well as the calcium channel block produced by diltiazem, result from the interaction of diltiazem with the same or similar receptor site(s).

Structural and physiological bases for effectivity of soybean nodules formed by fast-growing and slow-growing bacteria

Five weeks after planting, the total dry weight of the association between the soybean cultivar Maple Arrow and the slow-growing rhizobia, Bradyrhizobium japonicum USDA 16, was 1.6 times that with the fast-growing rhizobia, Rhizobium fredii QB1130. In contrast, with the uncultivated variety, 'Peking', the USDA 16 association possessed only 0.58 of the dry weight of the QB1130 association. These growth characteristics could not be fully explained in terms of number or mass of nodules formed. Rather, the specific nodule activity (rate of H2 evolution in Ar–O2 per unit nodule mass) was lower in the poorly effective symbioses ('Maple Arrow' × QB1130; 'Peking' × USDA 16). Nodules of the less effective symbioses were characterized by large deposits of starch in the cortex and in uninfected cells of the central zone, a thick cortical zone, relatively less infected cell area in the central zone, and fewer bacteria per unit crosssectional area of infected cell. Therefore, there were fewer bacteria per nodule in these symbioses. When total nitrogenase activities were expressed per bacteroid number or per bacteroid volume, no significant differences were observed among the four symbioses. These results indicate that the poor effectivity of the 'Maple Arrow' × QB1130 and 'Peking' × USDA 16 symbioses was due to a limitation of either bacterial release from the infection thread or bacterial proliferation within the infected cells.

Beta-adrenergic modulation in the heart. Independent regulation of K and Ca channels

The temperature-dependence of the actions of beta-receptor agonists and adenylate cyclase stimulation on both calcium and delayed rectifier potassium channel ionic currents were examined in patch-clamped guinea pig ventricular myocytes. We report that temperature can separate the beta-receptor mediated modulation of potassium and calcium channels. Receptor-mediated increases in the delayed rectifier potassium current, but not the calcium current were very temperature-dependent over the range of 19 to 32 degrees C. At room temperature (19-22 degrees C) the beta-agonist isoproterenol produced a large enhancement of the calcium current but had no effect on the delayed rectifier current. In contrast, at warmer temperatures (28-32 degrees C) both currents increased in the presence of the agonist. This temperature-sensitivity also existed for direct stimulation of adenylate cyclase by forskolin. Thus, cardiac calcium and potassium channels appear to be independently regulated during adrenergic stimulation.

Carbohydrate supply and n(2) fixation in soybean : the effect of varied daylength and stem girdling

When arrival of shoot supplied carbohydrate to the nodulated root system of soybean was interrupted by stem girdling, stem chilling, or leaf removal, nodule carbohydrate pools were utilized, and a marked decline in the rates of CO(2) and H(2) evolution was observed within approximately 30 minutes of treatment. Nodule excision studies demonstrated that the decline in nodulated root respiration was associated with nodule rather than root metabolism, since within 3.5 hours of treatment, nodules respired at less than 10% of the initial rates. Apparently, a continuous supply of carbohydrate from the shoot is required to support nodule, but not root, function. Depletion of nodular carbohydrate pools was sufficient to account for the (diminishing) nodule respiration of girdled plants. Of starch and soluble sugar pools within the whole plant, only leaf starch exhibited a diurnal variation which was sufficient to account for the respiratory carbon loss of nodules over an 8 hour night. Under 16 hour nights, or in continuous dark, first the leaf starch pools were depleted, and then nodule starch reserves declined concomitant with a decrease in the rates of CO(2) and H(2) evolution from the nodules. Nodule soluble sugar levels were maintained in dark treated plants but declined in girdled plants. The depletion of starch in root nodules is an indicator of carbohydrate limitation of nodule function.

Suppression of charge movement by calcium antagonists is not related to calcium channel block

The calcium channel-inhibiting drugs nitrendipine and diltiazem represent two important classes of organic calcium antagonists. In the present study, the effect of these drugs on calcium currents and charge displacement currents in bullfrog semitendinosus muscle fibers was examined using a vaseline gap voltage clamp. Nitrendipine (10 microM) reduced the quantity of charge that moved both during the ON phase (QON) and the OFF phase (QOFF) of charge movement. This action appeared to be most selective for QON. However, at this same concentration, nitrendipine had no blocking action on inward calcium currents. In contrast to these findings, diltiazem blocked calcium currents in a concentration-dependent manner, while slightly increasing the quantity of charge moved during QON and QOFF. The enhancement of charge movement by diltiazem resulted from two actions. First, diltiazem shifted the voltage-dependence of charge movement to more negative potentials. Second, diltiazem increased the maximum amount of charge moved.

Effect of calcium antagonist drugs on calcium currents in mammalian skeletal muscle fibers

The calcium channel-inhibiting drugs diltiazem, verapamil and nitrendipine represent three general classes of organic calcium antagonists. In the present study, the effect of these drugs on calcium currents (ICa++) in rabbit sternomastoid muscle fibers was examined. ICa++ were recorded at room temperature using a vaseline gap voltage clamp. ICa++ measured had similar kinetics to those reported in rat skeletal muscle, were partially blocked by 0.5 mM CdCI2 and could be reduced by substitution of Mg++ for Ca++. Diltiazem reversibly blocked ICa++ in a concentration-dependent manner with the 50% inhibitory concentration (IC50) being 63 microM. Verapamil was slightly more potent with approximately 50% block of ICa++ occurring at 10 microM. In contrast, nitrendipine at concentrations from 1 to 10 microM had no blocking action on ICa++, even after 20 min of exposure. Thus, although Ca++ channels in mammalian skeletal muscle fibers are readily blocked by cadmium, diltiazem and verapamil, these channels appear to be insensitive to the dihydropyridine compound nitrendipine.

Carbon and nitrogen assimilation and partitioning in soybeans exposed to low root temperatures

Low root temperature effects on vegetative growth of soybean (Harosoy 63 x Rhizobium japonicum USDA 16) were examined in 35 day old plants exposed to temperatures of 15 degrees C (shoots at 25 degrees C) for an 11 day period. Duing this period various aspects of C and N assimilation and partitioning were monitored including shoot night and nodulated root respiration, C and N partitioning to six plant parts, C(2)H(2) reduction, H(2) evolution, leaf area, transpiration, net photosynthesis, and N(2) fixation. The low temperature treatment resulted in a decrease in the net rate of N(2) fixation but nitrogenase relative efficiency increased. In response, the plant retained N in the tissues of the nodulated root and decreased N partitioning to young shoot tissues, thereby inducing the remobilization of N from older leaves, and reducing leaf area development. The leaf area specific rate of net photosynthesis was not affected over the study period; however, shoot and nodulated root respiration declined. Consequently, C accumulated in mature leaves and stems, partly in the form of increased starch reserves. Three possibilities were considered for increasing low temperature tolerance in nodulated soybeans: (a) decrease in temperature optima for nitrogenase, (b) increased development of nodules and N(2) fixation capacity at low temperature, and (c) alterations in the pattern of C and N partitioning in response to low temperature conditions.

Diltiazem potentiates mechanical activity in mammalian skeletal muscle

The calcium antagonist drug diltiazem produces a concentration dependent increase in twitch amplitude and a decrease in the mechanical threshold in mouse and rat skeletal muscle fibers in vitro. The greater potency of the d-cis isomer of diltiazem over the 1-cis isomer suggests that the effects of diltiazem are specific and may result from its binding to a specific receptor.

Intracellular pH mediates action of insulin on glycolysis in frog skeletal muscle

In a glucose-free bicarbonate Ringer (5% CO2 in N2), insulin increased intracellular pH (pHi), as determined by [14C]dimethadione, by 0.12 +/- 0.02 and stimulated glycolysis, as monitored by anaerobic lactate production, by 42.9 +/- 3.5% in paired frog sartorius muscles. The effect of insulin on glycolysis was shown to vary approximately linearly with log [Na+]0, being converted in 0.12 mM Na+ Ringer to a 51.5 +/- 8.4% inhibition of glycolysis. As the Na+ free-energy gradient was varied by decreasing [Na+]0 from 104 to 6.8 mM, the changes in glycolytic flux produced by insulin consistently paralleled the changes in pHi produced by the hormone. The relationship between the change in pHi and percent change in glycolytic flux was the same regardless of whether the effects were produced by insulin or by changing CO2. When glycolysis was either stimulated or inhibited, intracellular levels of fructose 6-phosphate varied inversely with glycolytic flux. This indicates that the effect on glycolysis of either insulin or changes in CO2 is due to a change in the activity of phosphofructokinase. The results support the model that the acute effect of insulin on glycolysis is mediated by a change in pHi, consequent to activation by insulin of Na:H exchange at the plasma membrane.