Seed Viability Constants for Groundnut

This research determined constants for a viability equationto predict the longevity of groundnut seeds and to improve themanagement of seedlot storage throughout the trading period.Seeds of the Brazilian cultivar ‘Tatu’ (Valenciabunch type) were tested. Nine moisture content levels (rangingfrom 2.4 to 12.8%) and three storage temperatures (40, 50 and65 °C) were used. Sub-samples for each moisture content-storagetemperature combination were sealed in laminated aluminium-foilpackets and stored in incubators until complete survival curveswere obtained. A reliable equation was obtained to predict groundnutseed longevity through the constantsK_E=6.177,C_W=3.426,C_H=0.0304andC_Q=0.000453.Copyright 1998 Annals of Botany Company Arachis hypogaeaL., seed longevity, seed storage, viability equation.     

Mining SARS-CoV protease cleavage data using non-orthogonal decision trees: a novel method for decisive template selection

Motivation: Although the outbreak of the severe acute respiratorysyndrome (SARS) is currently over, it is expected that it willreturn to attack human beings. A critical challenge to scientistsfrom various disciplines worldwide is to study the specificityof cleavage activity of SARS-related coronavirus (SARS-CoV)and use the knowledge obtained from the study for effectiveinhibitor design to fight the disease. The most commonly usedinductive programming methods for knowledge discovery from dataassume that the elements of input patterns are orthogonal toeach other. Suppose a sub-sequence is denoted as P₂P₁P_1'P_2',the conventional inductive programming method may result ina rule like ‘if P₁ = Q, then the sub-sequence is cleaved,otherwise non-cleaved’. If the site P₁ is not orthogonalto the others (for instance, P₂, P_1' and P_2'), the predictionpower of these kind of rules may be limited. Therefore thisstudy is aimed at developing a novel method for constructingnon-orthogonal decision trees for mining protease data. Result: Eighteen sequences of coronavirus polyprotein were downloadedfrom NCBI (http://www.ncbi.nlm.nih.gov). Among these sequences,252 cleavage sites were experimentally determined. These sequenceswere scanned using a sliding window with size k to generateabout 50 000 k-mer sub-sequences (for short, k-mers). The valueof k varies from 4 to 12 with a gap of two. The bio-basis functionproposed by Thomson et al. is used to transform the k-mers toa high-dimensional numerical space on which an inductive programmingmethod is applied for the purpose of deriving a decision treefor decision-making. The process of this transform is referredto as a bio-mapping. The constructed decision trees select about10 out of 50 000 k-mers. This small set of selected k-mers isregarded as a set of decisive templates. By doing so, non-orthogonaldecision trees are constructed using the selected templatesand the prediction accuracy is significantly improved. Availability: The program for bio-mapping can be obtained byrequest to the author. Contact: z.r.yang{at}exeter.ac.uk     

Effects of inhaled CO2 and added dead space on idiopathic central sleep apnea

Xie, Ailiang, Fiona Rankin, Ruth Rutherford, and T. DouglasBradley. Effects of inhaledCO₂ and added dead space on idiopathic central sleep apnea. J. Appl.Physiol. 82(3): 918-926, 1997.We hypothesizedthat reductions in arterial PCO₂ (Pa_CO2) below the apnea threshold play akey role in the pathogenesis of idiopathic central sleep apnea syndrome(ICSAS). If so, we reasoned that raisingPa_CO2 would abolish apneas in thesepatients. Accordingly, patients with ICSAS were studied overnight onfour occasions during which the fraction of end-tidalCO₂ and transcutaneous PCO₂ were measured: during room airbreathing (N1), alternating room airand CO₂ breathing(N2),CO₂ breathing all night(N3), and addition of dead space viaa face mask all night (N4).Central apneas were invariably preceded by reductions infraction of end-tidal CO₂. Bothadministration of a CO₂-enrichedgas mixture and addition of dead space induced 1- to 3-Torr increasesin transcutaneous PCO₂, whichvirtually eliminated apneas and hypopneas; they decreased from43.7 ± 7.3 apneas and hypopneas/h onN1 to 5.8 ± 0.9 apneas andhypopneas/h during N3(P < 0.005), from 43.8 ± 6.9 apneas and hypopneas/h during room air breathing to 5.9 ± 2.5 apneas and hypopneas/h of sleep duringCO₂ inhalation during N2 (P < 0.01), and to 11.6% of the room air level while the patients werebreathing through added dead space duringN4 (P < 0.005). Because raisingPa_CO2 through two different meansvirtually eliminated central sleep apneas, we conclude that centralapneas during sleep in ICSA are due to reductions inPa_CO2 below the apnea threshold.

     

A model of the spontaneously breathing patient: applications to intrinsic PEEP and work of breathing

Schuessler, Thomas F., Stewart B. Gottfried, and Jason H. T. Bates. A model of the spontaneously breathing patient: applications to intrinsic PEEP and work of breathing.J. Appl. Physiol. 82(5):1694-1703, 1997.Intrinsic positive end-expiratory pressure(PEEP_i) and inspiratory work ofbreathing (WI) are important factors in the management of severe obstructive respiratory disease. Weused a computer model of spontaneously breathing patients with chronicobstructive pulmonary disease to assess the sensitivity of measurementtechniques for dynamic PEEP_i(PEEP_{i dyn}) andWI to expiratory muscle activity(EMA) and cardiogenic oscillations (CGO) on esophageal pressure.Without EMA and CGO, bothPEEP_{i dyn} andWI were accurately estimated(r = 0.999 and 0.95, respectively). Addition of moderate EMA causedPEEP_{i dyn} andWI to be systematically overestimated by 141 and 52%, respectively. Furthermore, CGOintroduced large random errors, obliterating the correlation betweenthe true and estimated values for bothPEEP_{i dyn}(r = 0.29) andWI (r = 0.38). Thus the accurateestimation of PEEP_{i dyn} andWI requires steps to be taken toameliorate the adverse effects of both EMA and CGO. Taking advantage ofour simulations, we also investigated the relationship betweenPEEP_{i dyn} and staticPEEP_i(PEEP_{i stat}). ThePEEP_{i dyn}/PEEP_{i stat}ratio decreased as stress adaptation in the lung was increased,suggesting that heterogeneity of expiratory flow limitation isresponsible for the discrepancies betweenPEEP_{i dyn} andPEEP_{i stat} thathave been reported in patients with severe airwayobstruction.

     

Interaction of leg stiffness and surface stiffness during human hopping

Ferris, Daniel P., and Claire T. Farley. Interaction ofleg stiffness and surface stiffness during human hopping.J. Appl.Physiol. 82(1): 15-22, 1997.When mammals run,the overall musculoskeletal system behaves as a single linear "legspring." We used force platform and kinematic measurements todetermine whether leg spring stiffness(k_leg) isadjusted to accommodate changes in surface stiffness(k_surf) whenhumans hop in place, a good experimental model for examiningadjustments tok_leg in bouncinggaits. We found thatk_leg was greatlyincreased to accommodate surfaces of lower stiffnesses. The seriescombination ofk_leg andk_surf[total stiffness(k_tot)]was independent ofk_surf at a givenhopping frequency. For example, when humans hopped at a frequency of 2 Hz, they tripled theirk_leg on the leaststiff surface(k_surf = 26.1 kN/m; k_leg = 53.3 kN/m) compared with the most stiff surface(k_surf = 35,000 kN/m; k_leg = 17.8 kN/m). Values fork_tot were notsignificantly different on the least stiff surface (16.7 kN/m) and themost stiff surface (17.8 kN/m). Because of thek_leg adjustment,many aspects of the hopping mechanics (e.g., ground-contact time andcenter of mass vertical displacement) remained remarkably similardespite a >1,000-fold change ink_surf. This studyprovides insight into howk_leg adjustmentscan allow similar locomotion mechanics on the variety of terrainsencountered by runners in the natural world.

     

The signaling role of extracellular ATP and its dependence on Ca2+ flux in elicitation of Salvia miltiorrhiza hairy root cultures

The application of a polysaccharide elicitor from yeast extract,YE, to Salvia miltiorrhiza hairy root cultures induced transientrelease of ATP from the roots to the medium, leading to a dose-dependentincrease in the extracellular ATP (eATP) level. The eATP levelrose to a peak (about 6.5 nM with 100 mg l^–1 YE) at about10 h after YE treatment, but dropped to the control level 6h later. The elicitor-induced ATP release was dependent on membraneCa²⁺ influx, and abolished by the Ca²⁺ chelator EGTA or thechannel blocker La³⁺. The YE-induced H₂O₂ production was stronglyinhibited by reactive blue (RB), a specific inhibitor of membranepurinoceptors. On the other hand, the application of exogenousATP at 10–100 µM to the cultures also induced rapidand dose-dependent increases in H₂O₂ production and medium pH,both of which were effectively blocked by RB and EGTA. The non-hydrolyzableATP analog ATPS was as effective as ATP, but the hydrolyzedderivatives ADP or AMP were not so effective in inducing thepH and H₂O₂ increases. Our results suggest that ATP releaseis an early event and that eATP plays a signaling role in theelicitation of plant cell responses; Ca²⁺ is required for activationof the elicitor-induced ATP release and the eATP signal transduction.This is the first report on ATP release induced by a fungalelicitor and its involvement in the elicitor-induced responsesin plant cells.     

Ventilation distribution during histamine provocation

Verbanck, S., D. Schuermans, A. Van Muylem, M. Paiva, M. Noppen, and W. Vincken. Ventilation distribution during histamine provocation. J. Appl. Physiol. 83(6):1907-1916, 1997.We investigated ventilation inhomogeneity duringprovocation with inhaled histamine in 20 asymptomatic nonsmokingsubjects. We used N₂multiple-breath washout (MBW) to deriveparameters S_condand S_acin as ameasurement of ventilation inhomogeneity in conductive and acinar zonesof the lungs, respectively. A 20% decrease of forced expiratory volume in 1 s (FEV₁) was used todistinguish responders from nonresponders. In the responder group,average FEV₁ decreased by 26%,whereas S_condincreased by 390% with no significant change inS_acin. In thenonresponder group, FEV₁ decreasedby 11%, whereasS_cond increased by 198% with no significantS_acin change.Despite the absence of change inS_acin duringprovocation, baselineS_acin wassignificantly larger in the responder vs. the nonresponder group. Themain findings of our study are that during provocation largeventilation inhomogeneities occur, that the small airways affected bythe provocation process are situated proximal to the acinar zone wherethe diffusion front stands, and that, in addition to overall decreasein airway caliber, there is inhomogeneous narrowing of parallelairways.

     

Pliometric contraction-induced injury of mouse skeletal muscle: effect of initial length

Hunter, Kam D., and John A. Faulkner. Pliometriccontraction-induced injury of mouse skeletal muscle: effect of initial length. J. Appl. Physiol. 82(1):278-283, 1997.For single pliometric (lengthening) contractionsinitiated from optimal fiber length (L_f), the mostimportant factor determining the subsequent force deficit is the workinput during the stretch. We tested the hypothesis that regardless ofthe initial length, the force deficit is primarily a function of thework input. Extensor digitorum longus muscles of mice were maximallyactivated in situ and lengthened at 2 L_f /s from oneof three initial fiber lengths (90, 100, or 120% of L_f) to one ofthree final fiber lengths (150, 160, or 170% of L_f). Maximalisometric force production was assessed before and after the pliometriccontraction. No single mechanical factor, including thework input(r² = 0.34), was sufficient to explain the differences in force deficits observed among groups. Therefore, the force deficit appears to arisefrom a complex interaction of mechanicalevents. With the data grouped by initial fiber length,the correlation between the average work and the average force deficitwas high(r² = 0.97-0.99). Consequently, differences in force deficits among groups were best explained on the basis of the initial fiber length andthe work input during the stretch.

     

Conservation of bronchiolar wall area during constriction and dilation of human airways

Mitchell, R. W., E. Rühlmann, H. Magnussen, N. M. Muñoz, A. R. Leff, and K. F. Rabe. Conservation ofbronchiolar wall area during constriction and dilation of humanairways. J. Appl. Physiol. 82(3):954-958, 1997.We assessed the effect of smooth musclecontraction and relaxation on airway lumen subtended by the internalperimeter(A_i)and total cross-sectional area (A_o)of human bronchial explants in the absence of the potential lungtethering forces of alveolar tissue to test the hypothesis thatbronchoconstriction results in a comparable change ofA_i andA_o.Luminal area (i.e.,A_i) andA_owere measured by using computerized videomicrometry, and bronchial wallarea was calculated accordingly. Images on videotape were captured;areas were outlined, and data were expressed as internal pixel numberby using imaging software. Bronchial rings were dissected in 1.0- to1.5-mm sections from macroscopically unaffected areas of lungs frompatients undergoing resection for carcinoma, placed in microplate wellscontaining buffered saline, and allowed to equilibrate for 1 h.Baseline, A_o[5.21 ± 0.354 (SE)mm²], andA_i(0.604 ± 0.057 mm²) weremeasured before contraction of the airway smooth muscle (ASM) withcarbachol. MeanA_inarrowed by 0.257 ± 0.052 mm²in response to 10 µM carbachol (P = 0.001 vs. baseline). Similarly, A_onarrowed by 0.272 ± 0.110 mm²in response to carbachol (P = 0.038 vs. baseline; P = 0.849 vs. change inA_i).Similar parallel changes in cross-sectional area forA_iandA_owere observed for relaxation of ASM from inherent tone of otherbronchial rings in response to 10 µM isoproterenol. We demonstrate aunique characteristic of human ASM; i.e., both luminal and totalcross-sectional area of human airways change similarly on contractionand relaxation in vitro, resulting in a conservation of bronchiolarwall area with bronchoconstriction and dilation.

     

Vitamins, phytoplankton and bacteria: symbiosis or scavenging?

The conclusion that over 25% of global primary production dependson direct algal/bacterial symbiosis involving vitamin B₁₂ [Croftet al., (2005) Algae acquire vitamin B₁₂ through a symbioticrelationship with bacteria. Nature, 438, 90–93] is patentlyfalse, for it is based on a misconception of the probable levelof the vitamin B₁₂ requirement in marine pelagic algae. A reviewof the various published attempts at measuring this requirementsuggests that it is likely to be so low that oceanic and coastalconcentrations of the vitamin would usually be sufficient tosustain the populations that occur without the assistance ofdirect algal/bacterial symbiosis. The levels measured are discussedin relation to method (batch or continuous culture) and protocolsused. Requirement values considered by the author to be acceptablerange from 0.1 to 0.3 pM for the vitamin growth saturation constant(K_S) and from 30 to 100 µL algal biomass pmol^–1vitamin for the yield.     

When does the lung die? Kfc, cell viability, and adenine nucleotide changes in the circulation-arrested rat lung

Jones, David R., Randy M. Becker, Steve C. Hoffmann, John J. Lemasters, and Thomas M. Egan. When does the lungdie? K_fc, cellviability, and adenine nucleotide changes in the circulation-arrested rat lung. J. Appl. Physiol. 83(1):247-252, 1997.Lungs harvested from cadavericcirculation-arrested donors may increase the donor pool for lungtransplantation. To determine the degree and time course ofischemia-reperfusion injury, we evaluated the effect ofO₂ ventilation on capillarypermeability [capillary filtration coefficient(K_fc)],cell viability, and total adenine nucleotide (TAN) levels in in situcirculation-arrested rat lungs.K_fc increased with increasing postmortem ischemic time(r = 0.88). Lungs ventilated withO₂ 1 h postmortem had similarK_fc andwet-to-dry ratios as controls. Nonventilated lungs had threefold(P < 0.05) and sevenfold (P < 0.0001) increases inK_fc at 30 and 60 min postmortem compared with controls. Cell viability decreased inall groups except for 30-min postmortemO₂-ventilated lungs. TAN levelsdecreased with increasing ischemic time, particularly in nonventilatedlungs. Loss of adenine nucleotides correlated with increasingK_fc values (r = 0.76). This study indicates thatlungs retrieved 1 h postmortem may have normalK_fc withpreharvest O₂ ventilation. Therelationship betweenK_fc and TANsuggests that vascular permeability may be related to lung TAN levels.

     

Zone of apposition in the passive diaphragm of the dog

Boriek, Aladin M., Joseph R. Rodarte, and Susan S. Margulies. Zone of apposition in the passive diaphragm of thedog. J. Appl. Physiol. 81(5): 1929-1940, 1996.Wedetermined the regional area of the diaphragmatic zone of apposition(ZAP) as well as the regional craniocaudal extent of the ZAP(ZAP_ht) of the passive diaphragm in six paralyzedanesthetized beagle dogs (8-12 kg) at residual lung volume (RV),functional residual capacity (FRC), FRC + 0.25 and FRC + 0.5 inspiratory capacity, and total lung capacity (TLC) in prone and supinepostures. To identify the caudal boundary of the ZAP, 17 lead markers(1 mm) were sutured to the abdominal side of the costal and cruraldiaphragms around the diaphragm insertion on the chest wall. Two weekslater, the dogs' caudal thoraces were scanned by the use of thedynamic spatial reconstructor (DSR), a prototype fast volumetric X-raycomputer tomographic scanner, developed at the Mayo Clinic. Thethree-dimensional spatial coordinates of the markers were identified(±1.4 mm), and the cranial boundary of the ZAP was determined from30-40 1.4-mm-thick sagittal and coronal slices in each DSR image.We interpolated the DSR data to find the position of the cranial andcaudal boundaries of the ZAP every 5° around the thorax and computedthe distribution of regional variation of area of the ZAP andZAP_ht as well as the total area of ZAP. TheZAP_ht and area of ZAP increased as lung volume decreasedand were largest near the lateral extremes of the rib cage. We measuredthe surface area of the rib cage cephaled to the ZAP(A_L) in both postures in another six beagle dogs(12-16 kg) of similar stature, scanned previously in the DSR. Weestimated the entire rib cage surface area(A_rc = A_ZAP +A_L). The A_ZAP as a percentageof A_rc increased more than threefold as lung volumedecreased from TLC to RV, from ~9 to 29% of A_rc.

     

Effect of ingested sodium bicarbonate on muscle force, fatigue, and recovery

Verbitsky, O., J. Mizrahi, M. Levin, and E. Isakov.Effect of ingested sodium bicarbonate on muscle force, fatigue, and recovery. J. Appl. Physiol. 83(2):333-337, 1997.The influence of acute ingestion ofNaHCO₃ on fatigue and recovery ofthe quadriceps femoris muscle after exercise was studied in six healthymale subjects. A bicycle ergometer was used for exercising under three loading conditions: test A, loadcorresponding to maximal oxygen consumption; testB, load in test A + 17%; test C, load intest B but performed 1 h after acuteingestion of NaHCO₃.Functional electrical stimulation (FES) was applied to provokeisometric contraction of the quadriceps femoris. The resulting kneetorque was monitored during fatigue (2-min chronic FES) and recovery (10-s FES every 10 min, for 40 min). Quadriceps torques were higher inthe presence of NaHCO₃(P < 0.05): withNaHCO₃ the peak, residual, andrecovery (after 40 min) normalized torques were, respectively, 0.68 ± 0.05 (SD), 0.58 ± 0.05, and 0.73 ± 0.05; withoutNaHCO₃ the values were 0.45 ± 0.04, 0.30 ± 0.06, and 0.63 ± 0.06. The increasedtorques obtained after acute ingestion ofNaHCO₃ indicate the possibleexistence of improved nonoxidative glycolysis in isometric contraction,resulting in reduced fatigue and enhanced recovery.

     

Letters to the Editor

The following is the abstract of the article discussed in thesubsequent letter:

Verbanck, S., D. Schuermans, A. Van Muylem, M. Paiva, M. Noppen, and W. Vincken. Ventilation distribution duringhistamine provocation. J. Appl. Physiol.83(6):1907-1916, 1997.We investigated ventilation inhomogeneityduring provocation with inhaled histamine in 20 asymptomatic nonsmokingsubjects. We used N₂ multiple-breath washout (MBW) toderive parameters S_cond andS_acin as a measurement of ventilationinhomogeneity in conductive and acinar zones of the lungs,respectively. A 20% decrease of forced expiratory volume in 1 s(FEV₁) was used to distinguish responders fromnonresponders. In the responder group, average FEV₁decreased by 26%, whereas S_cond increased by390% with no significant change in S_acin. In the nonresponder group, FEV₁ decreased by 11%, whereasS_cond increased by 198% with no significantS_acin change. Despite the absence of change inS_acin during provocation, baselineS_acin was significantly larger in the respondervs. the nonresponder group. The main findings of our study are thatduring provocation large ventilation inhomogeneities occur, that thesmall airways affected by the provocation process are situated proximalto the acinar zone where the diffusion front stands, and that, inaddition to overall decrease in airway caliber, there is inhomogeneousnarrowing of parallel airways.

     

Isoproterenol attenuates high vascular pressure-induced permeability increases in isolated rat lungs

Parker, James C., and Claire L. Ivey.Isoproterenol attenuates high vascular pressure-inducedpermeability increases in isolated rat lungs. J. Appl.Physiol. 83(6): 1962-1967, 1997.To separate thecontributions of cellular and basement membrane components of thealveolar capillary barrier to the increased microvascular permeabilityinduced by high pulmonary venous pressures (Ppv), we subjected isolatedrat lungs to increases in Ppv, which increased capillary filtrationcoefficient(K_fc) withoutsignificant hemorrhage (31 cmH₂O)and with obvious extravasation of red blood cells (43 cmH₂O). Isoproterenol (20 µM)was infused in one group (Iso) to identify a reversible cellularcomponent of injury, and residual blood volumes were measured to assessextravasation of red blood cells through ruptured basement membranes.In untreated lungs (High Ppv group),K_fc increased 6.2 ± 1.3 and 38.3 ± 15.2 times baseline during the 31 and 43 cmH₂O Ppv states. In Iso lungs, K_fc was 36.2%(P < 0.05) and 64.3% of that in theHigh Ppv group at these Ppv states. Residual blood volumes calculatedfrom tissue hemoglobin contents were significantly increased by53-66% in the high Ppv groups, compared with low vascularpressure controls, but there was no significant difference between HighPpv and Iso groups. Thus isoproterenol significantly attenuatedvascular pressure-induced K_fc increases atmoderate Ppv, possibly because of an endothelial effect, but it did notaffect red cell extravasation at higher vascular pressures.

     

Thromboxane A2 mediates increased pulmonary microvascular permeability after intestinal reperfusion

Turnage, Richard H., John L. LaNoue, Kevin M. Kadesky, YanMeng, and Stuart I. Myers. ThromboxaneA₂ mediates increased pulmonarymicrovascular permeability after intestinal reperfusion. J. Appl. Physiol. 82(2): 592-598, 1997.This study examines the hypothesis that intestinal reperfusion(IR)-induced pulmonary thromboxane A₂(TxA₂) release increases localmicrovascular permeability and induces pulmonary vasoconstriction.Sprague-Dawley rats underwent 120 min of intestinal ischemia and 60 minof IR. Sham-operated animals (Sham) served as controls. After IR orSham, the pulmonary vessels were cannulated, and the lungs wereperfused in vitro with Krebs buffer. Microvascular permeability wasquantitated by determining the filtration coefficient(K_f),and pulmonary arterial (Ppa), venous (Ppv), and capillary (Ppc)pressures were measured to calculate vascular resistance (Rt). Afterbaseline measurements, imidazole(TxA₂ synthase inhibitor) orSQ-29,548 (TxA₂-receptorantagonist) was added to the perfusate; thenK_f, Ppa, Ppv, and Ppc were again measured. TheK_fof lungs from IR animals was four times greater than that of Sham(P = 0.001), and Rt was 63% greaterin the injured group (P = 0.01). Pc of IR lungs was twice that of controls (5.4 ± 1.0 vs. 2.83 ± 0.3 mmHg, IR vs. Sham, respectively; P < 0.05). Imidazole or SQ-29,548 returnedK_fto baseline measurements (P < 0.05)and reduced Rt by 23 and 17%, respectively(P < 0.05). IR-induced increases in Pc were only slightly reduced by 500 µg/ml imidazole (14%;P = 0.05) but unaffected by lowerdoses of imidazole (5 or 50 µg/ml) or SQ-29,548. These data suggestthat IR-induced pulmonary edema is caused by both increasedmicrovascular permeability and increased hydrostatic pressure and thatthese changes are due, at least in part, to the ongoing release ofTxA₂.

     

LabHEART: an interactive computer model of rabbit ventricular myocyte ion channels and Ca transport

An interactive computer program,LabHEART, was developed to simulate the action potential (AP), ioniccurrents, and Ca handling mechanisms in a rabbit ventricular myocyte.User-oriented, its design allows switching between voltage and currentclamp and easy on-line manipulation of key parameters to change theoriginal formulation. The model reproduces normal rabbit ventricularmyocyte currents, Ca transients, and APs. We also changed parameters to simulate data from heart failure (HF) myocytes, including reduced transient outward (I_to) and inward rectifying Kcurrents (I_K1), enhanced Na/Ca exchangeexpression, and reduced sarcoplasmic reticulum Ca-ATPase function, butunaltered Ca current density. These changes caused reduced Ca transientamplitude and increased AP duration (especially at lower frequency) asobserved experimentally. The model shows that the increased Na/Caexchange current (I_NaCa) in HF lowers theintracellular [Ca] threshold for a triggered AP from 800 to 540 nM. Similarly, the decrease in I_K1reduces the threshold to 600 nM. Changes in I_tohave no effect. Combining enhanced Na/Ca exchange with reducedI_K1 (as in HF) lowers the threshold to triggeran AP to 380 nM. These changes reproduce experimental results inHF, where the contributions of different factors are notreadily distinguishable. We conclude that the triggered APs thatcontribute to nonreentrant ventricular tachycardia in HF are dueapproximately equally (and nearly additively) to alterations inI_NaCa and I_K1. A freecopy of this software can be obtained athttp://www.meddean.luc.edu/lumen/DeptWebs/physio/bers.html.

     

Thermodynamic Roles of Solubility in Taste Responses of Amino Acids

Bitter, sour and sweet responses of amino acids were relatedto their solubilities S_w, which are virtually equal to the reciprocalsof activity coefficients at infinite dilution in water _w, andalso related to their excess partial molar entropies of transferTS_t^E. Chem. Senses 21: 405–409, 1996. Present address: 5-32-12 Tamanawa, Kamakura-shi, 247 Japan     

Appropriate thermal manipulations eliminate tremors in rats recovering from halothane anesthesia

Grahn, D. A., M. C. Heller, J. E. Larkin, and H. C. Heller.Appropriate thermal manipulations eliminate tremors in ratsrecovering from halothane anesthesia. J. Appl.Physiol. 81(6): 2547-2554, 1996.Tremors arecommon in mammals emerging from anesthesia. To determine whetherappropriate thermal manipulations immediately before emergence fromanesthesia are sufficient to eliminate these tremors,electroencephalographic (EEG) and electromyographic (EMG) activities,hypothalamic temperature (T_hy),and O₂ consumption were monitoredin 12 rats recovering from halothane anesthesia under three thermalregimes. EEG and EMG activities were recorded throughout anesthesia andserved as feedback signals for controlling anesthetic depth. Duringanesthesia, T_hy was either1) allowed to fall to32-34°C, 2) maintained at37-39°C, or 3) allowed to fall to 32-34°C and then raised to 37-39°C. Whenhypothermic on emergence from anesthesia, all of the animals exhibitedpostanesthetic tremors that persisted untilT_hy values returned tonormothermia. None of the animals expressed postanesthetic tremors whennormothermic on emergence from anesthesia. In addition, the timebetween emergence from anesthesia (as determined by EEG/EMG parameters)and the initiation of coordinated motor activities was significantlydecreased in the normothermic animals.