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Biomedical subjects

D J Marsh

Publications and source records attributed to D J Marsh.

At least 145 records · Page 8Linked to original sources
PubMed1986

Intrarenal mechanisms mediating pressure natriuresis: role of angiotensin and prostaglandins.

The ability of the kidney to increase sodium and water excretion in response to increases in perfusion pressure has been recognized for more than 50 years. Because glomerular filtration rate is tightly autoregulated, pressure natriuresis occurs as the result of decreased tubular sodium reabsorption rather than increased filtered load. Micropuncture and microperfusion data support the contention that acute changes in arterial pressure can alter proximal tubule reabsorption; however, studies have failed to show a consistent association between changes in sodium excretion and peritubular, interstitial, or tubular pressures. Thus, the specific intrarenal mechanism for the change in tubular reabsorption in response to an acute change in arterial pressure does not appear to be related to the peritubular physical factors at the level of outer cortical nephrons. The possible roles of angiotensin and prostaglandins as humoral mediators of pressure natriuresis are considered in this report. Although angiotensin II is a powerful modulator of the slope of the pressure natriuresis relationship, the responsiveness of sodium excretion to arterial pressure is actually enhanced by angiotensin-converting enzyme inhibitors. These data suggest that angiotensin does not mediate the basic phenomenon. Recent experiments indicate that intrarenal prostaglandins also modulate the magnitude of the pressure natriuresis relationship, but these hormones do not appear to be essential for its basic manifestation.

Absorption↗
PubMed1985

Computer-based determination of size and shape in living cells.

Measurement of cell volume in living epithelial cells has become an important technique in studies of membrane transport processes that function in cell volume regulation. Planimetry of video images of optical sections enables the measurement of the cross sectional area of each section. Cell volume is calculated from the measured area of each section and the known focus displacements. In the past the measurement of cross section area has been done by manual positioning of a cursor superimposed on the video image. Each experiment generates approximately 200 images in which two or more cells may be analysed. We have developed a computer-based method that uses one image as a template, and allows automated area determination of successive images by template matching and digital image processing. This new method is comparable to the older method in speed and accuracy, but requires much less effort from the experimenter.

Animals↗
PubMed1985

Proteolytic digestion patterns of "soluble" and "detergent-soluble" bovine caudate nucleus acetylcholinesterases.

The structures of purified "soluble" and "detergent-soluble" bovine caudate nucleus acetylcholinesterases were compared by peptide mapping on polyacrylamide gels. The digestion products generated from the two acetylcholinesterases on proteolysis by a given protease (Staphylococcus aureus V8 protease, alpha-chymotrypsin, or papain) are remarkably similar as judged from the electrophoretic band patterns. We conclude that the "soluble" and "detergent-soluble" acetylcholinesterases from bovine caudate nucleus share a common evolutionary origin.

Acetylcholinesterase↗
PubMed1985

Polarity of volume-regulatory increase by Necturus gallbladder epithelium.

Necturus gallbladder epithelial cells respond to the presence of a hypertonic perfusate in either bathing solution by first shrinking due to osmotic water loss and then swelling back to their original volume (volume-regulatory increase). Previous investigations involving increases in the osmolality of the mucosal bath had suggested that volume-regulatory increase was due to the activation of ion exchangers in the apical cell membrane. In the present study the sidedness of the transport processes involved in volume-regulatory increase was investigated. The osmolality of the serosal bath was increased by 18% either in the absence of HCO3- or when an inhibitor of volume-regulatory increase, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), was added to the mucosal or serosal bath. Volume regulation was HCO3- dependent. DIDS was only effective in inhibiting volume regulation when it was added to mucosal bathing solution, suggesting that volume-regulatory increase depended on transport across the apical membrane. Volume-regulatory increase could also be activated by first swelling the cells in hypotonic solution and then returning the tissue to control Ringer solution. The volume-regulatory increase that occurred upon return to control Ringer was also shown to be sensitive to DIDS in the mucosal bath.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1985

Ultra- and circadian fluctuations in arterial pressure and electromyogram in conscious dogs.

Mean arterial blood pressure was measured for 2 days in conscious dogs to estimate the frequency of ultradian fluctuations and to compare the magnitudes of the ultra- and circadian fluctuations. The ultradian fluctuation had an average frequency of 0.38 +/- 0.04 cycle/h and 60% more power than the circadian rhythm. The ultradian fluctuation was consistently more powerful during daylight than nighttime hours, but there was no consistent change in the frequency with time of day. Electromyogram (EMG) activity was also measured to test a possible causal relationship between the two variables. There were both circ- and ultradian fluctuations in EMG activity, and the peak cross-spectral power was also in these frequency bands. The coherence function was also high, but the phase angle between the two variables was so variable, both in sign and in magnitude, that it was judged unlikely that there was tight coupling between them.

Animals↗
PubMed1984

Extracellular fluid expansion and autoregulation in nephrotoxic serum nephritis in rats.

Previous studies of the early autologous phase of bilateral nephrotoxic serum nephritis (NSN) in rats showed that whole kidney and single nephron glomerular filtration rate (GFR) were maintained at normal levels despite a 60% reduction in the product of surface area and hydraulic permeability (Kf). Factors responsible for this compensation were an increase of net ultrafiltration pressure, due primarily to an increased glomerular capillary pressure (PGC). This study was designed to investigate some possible causes of the compensation. Rats with bilateral NSN and normal GFR had an increased extracellular fluid volume (ECFV) 2 weeks after induction of NSN; control subjects did not change. To determine whether this ECFV expansion was responsible for triggering the compensation, we developed a unilateral NSN model with one diseased and one normal kidney. Unilaterally diseased rats did not experience an increase of ECFV. Values of Kf were 0.069 +/- 0.012 nl sec-1 mm Hg-1 in control subjects, 0.037 +/- 0.005 in bilateral NSN, and 0.043 +/- 0.006 in unilateral NSN. The elevation in PGC was the same in unilateral NSN as in bilateral NSN subjects and the same was true for the hydrostatic pressure difference across glomerular capillaries (delta P). Furthermore, in paired measurements on both kidneys of rats with unilateral NSN, PGC was significantly higher in the unilaterally diseased kidney than in the nondiseased kidney; sham control subjects had no difference. These results are interpreted to indicate that the signal that causes elevation of net ultrafiltration pressure is not a consequence of a systemic effect of NSN, but arises within the diseased kidney itself. To determine whether that signal involved some change in the mechanisms mediating autoregulation measurements were made of the response of whole kidney GFR and RBF to acute changes in arterial BP. Control rats and rats with NSN autoregulated both GFR and blood flow equally well. Tubuloglomerular feedback was studied by microperfusing loops of Henle and measuring proximal stop-flow pressure and early proximal flow rate. Stop-flow pressure was 4.0 mm Hg higher in rats with NSN at a loop perfusion rate of 10 nl/min, approximately the same difference that was found by direct measurement of PGC, but the sensitivity of response to changes in perfusion rate was the same in NSN as in control subjects. Finally, end proximal tubule flow rate was higher in NSN than in control subjects reflecting decreased proximal reabsorption. Thus, a normal feedback mechanism receives a signal that should cause afferent arteriolar constriction in NSN rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Computer simulation of renal countercurrent systems.

The history of mathematical modeling of renal countercurrent systems is briefly outlined. Several examples are cited and discussed. These include efforts at parameter estimation and experimental design with models. The goal of this work was the evaluation of hypotheses of hypertonic urine formation. The argument is made that computer simulation with reasonably isomorphic models can be used in a variety of ways, but that one indispensable role for this approach is to provide a test of the quantitative sufficiency of hypotheses. Hypotheses of hypertonic urine formation that do not consider active transport in thin ascending limbs do not pass this test. A new proposal is suggested in which the energy for NaCl reabsorption from thin ascending limbs is derived from dissipation of a urea gradient via an antiport.

Arginine Vasopressin↗
PubMed1983

Comparative affinity chromatography of acetylcholinesterases from five vertebrate species.

The efficacy of N-methylacridinium affinity chromatography in the purification of acetylcholinesterases from chicken, rat, calf and human brain and from the electric organ of the electric fish Torpedo marmorata has been investigated. Retention of the enzymes on the N-methylacridinium columns exceeded 90% in all instances except for the chicken enzyme, where 40-80% retention was observed depending on the acridinium concentration. Sucrose density gradient centrifugation profiles revealed no difference between the distribution of molecular forms in the crude extracts and in the partially purified fractions eluted from the columns by decamethonium iodide.

Acetylcholinesterase↗
PubMed1983

Skeletal muscle myosins from the yak (Bos grunniens), cattle (Bos taurus) and their hybrids.

The skeletal muscle myosins of the yak (Bos grunniens), of cattle (Bos taurus) and of their first and second filial generation hybrids have been studied by ATPase measurements, fluorescence spectroscopy, near-ultraviolet circular dichroism and peptide mapping on polyacrylamide gels. The ATPase activities, the intrinsic tryptophan fluorescence enhancement upon addition of ATP and the circular dichroism spectra of the four myosins were closely comparable. Peptide maps of the myosin heavy chains indicate extensive sequence homologies but do reveal differences between the myosins of the yak and cattle.

Adenosine Triphosphatases↗
PubMed1983

Autoregulation in vasa recta of the rat kidney.

Vasa recta blood flow autoregulation was studied by measuring flow velocity in individual vessels on the papilla surface with a video adaptation of the dual-slit erythrocyte velocity method. Vessel diameter did not vary with arterial pressure in the range of 60-150 mmHg, allowing the calculation of the ratio of flows in a single vessel at two pressures from the ratio of velocities. Flow velocity in single vasa recta increased with arterial pressure to 75 mmHg, remained constant in the range of 75-125 mmHg, and increased with higher pressures. In a second series of animals, whole kidney blood flow auto-regulated above 90 mmHg. Vasa recta and whole kidney flow patterns were not changed by extracellular fluid volume expansion. Volume expansion caused a greater increase in ascending than in descending vasa recta flow, reflecting the volume load from enhanced collecting duct reabsorption in diuresis. In a final series, Na excretion varied with arterial pressure in the range of 90-130 mmHg. Because vasa recta velocity remains constant within this range, pressure diuresis cannot be caused by the lack of autoregulation of vasa recta blood flow, at least to 130 mmHg.

Animals↗
PubMed1982

Fluorescently labeled myosin subfragment 1: identification of the kinetic step associated with the adenosine 5'-triphosphate induced fluorescence decrease.

Marsh, and Lowey [Marsh, D. J., & Lowey, S. (1980) Biochemistry 19, 774-784] introduced a fluorescence label, 5-(iodoacetamido)fluorescein (IAF), into the alkali 1 light chain of myosin subfragment 1 (S-1) without perturbing the K+-Ca2+, or actin-activated ATPase activities of the labeled S-1. They also found that the addition of MgATP to the labeled S-1 led to a 6-10% decrease in the fluorescence of the bound IAF label. In the present study, we investigated the pre-steady-state kinetics of the fluorescence decrease of the IAF label caused by the binding of MgATP to the labeled S-1. Our results show that most of the decrease in IAF fluorescence is caused by the ATP-hydrolysis step. This implies that a conformational change in the S-1 molecular associated with ATP hydrolysis has led to a change in the microenvironment of the IAF fluorophore bound to the alkali 1 light chain.

Actins↗
PubMed1982

Frequency response of autoregulation.

To estimate the frequency response of autoregulation and to test whether macula densa feedback alone mediates renal blood flow (RBF) autoregulation in rats, we imposed sudden increases (10 to 20 mm Hg) in arterial pressure (AP) and compared the time courses of renal vascular resistance (RVR) changes and of flow changes at the macula densa. RVR decreased abruptly after the AP increase, but returned to control levels in less than 1 sec, continued to increase, reaching 50% completion within 3 sec, and achieved final values 15 to 20 sec after AP change. To predict transient changes in tubule flow, we derived a model of pressure and flow and combined it with measurements of tubule pressure made during AP steps. With these measured pressures as inputs, the model predicted a prompt rise in GFR followed by a decline that returned GFR halfway to control values within 3 to 4 sec and more slowly thereafter. Predicted early distal flow increased perceptibly only after 1 sec and rose slowly thenceforth. The disturbance in early distal flow appears to arrive too late to signal the rapid changes in RVR. Some other mechanism, possibly myogenic, must have intervened. The results suggest that two mechanisms mediate autoregulation, each with a different response time. The putative myogenic mechanism is about one order of magnitude faster than the macula densa.

Animals↗
PubMed1980

Fluorescence energey transfer in myosin subfragment-1.

Fluorescent probes have been selectively introduced into skeletal muscle myosin subfragment-1 and the fluorescence emission characteristics of the labeled products studied. The fluorophores employed were the thiol-specific reagents N-[[(iodoacetyl)aminolethyl-5-naphthylamine-1-sulfonic acid and 5-(iodoacetamido)fluorescein, the spectral properties of which render them a particularly effective donor-acceptor pair in Förster energy-transfer studies. Alkali 1 light chain, labeled at a single cysteine with either of these probes, was incorporated into chymotryptic subfragment-1 by the exchange procedure of Wagner & Weeds [Wagner, P.D., & Weeds, A.G. (1977) J. Mol. Biol. 109, 455-473]. The resultant, fluorescently labeled subfragment-1 was isolated by ion-exchange chromatography. Determination of the extent of incorporation by extinction and fluorescence indicated that greater than 80% of the subfragment-1 population possessed a fluorescently labeled alkali 1 light chain. The introduction of labeled alkali 1 did not perturb the K+-, Ca2+-, or actin-activated adenosine triphosphatases of subfragment-1. The addition of adenosine triphosphate (ATP), liganded by various cations, to this singly labeled subfragment-1 induced a 6-10% decrease in the fluorescence intensity of the extrinsic chromophore. An intensity decrease of approximately 4% was obtained when the hydrolysis of ATP was complete, and also upon direct addition of adenosine diphosphate. The ATP analogue adenylyl imidodiphosphate induced a decrease of approximately 7% in intensity. The addition of F-actin to the subfragment-1 in the presence of MgATP elicited no further fluorescence intensity change. A second, appropriate fluorophore was introduced into the singly labeled subfragment-1 at the SH1 thiol on the heavy chain. Förster energy transfer was observed between this labeled site and the fluorophore previously introduced on the alkali 1 light chain. The measured efficiency of energy transfer indicated that the two fluorophores were approximately 40 A apart. The same value was obtained upon reversal of the donor and acceptor attachment sites, suggesting that the uncertainty in the calculated distance introduced by the choice of orientation factor is probably less than 20%. Steady-state observations did not reveal any obvious change in this distance upon the addition of MgATP and then F-actin to the doubly labeled subfragment-1.

Adenosine Triphosphatases↗
PubMed1980

Cause of glucose oscillations during glucose infusion: periodic variation in glucose uptake.

Constant infusion of glucose (10 mg . kg-1 . min-1) into conscious, intact dogs induced oscillations in the plasma concentrations of glucose and insulin. Glucose rose from basal (98 +/- 1 mg/dl) and, after 3 h, entered oscillations that persisted until the end of the 9-h glucose infusion. Between 240 and 540 min, glucose fluctuated by +/- 17 mg/dl about a mean value of 143 +/- 2 mg/dl; frequency of the glucose oscillation was 0.54 +/- 0.03 cycles/h. During the same time interval, insulin increased from basal 13 +/- 2 mu U/ml to mean 46 +/- 4 mu U/ml. Insulin oscillated at an amplitude (peak-to-peak) of 48 mu U/ml, with frequency not different from that of glucose (0.60 +/- 0.09 cycles/h). The oscillation in glucose "led" the insulin oscillation by 22 +/- 5 min. In three animals, [2-3H]glucose was infused along with unlabeled glucose during oscillations, and it was determined that almost all (98%) of the glucose appearance was from the exogenous infusion. Thus varying endogenous glucose production was ruled out as a contributory factor to the glucose oscillation. Total glucose uptake (Rd) fluctuated periodically at the same frequency as glucose and insulin (0.56 +/- 0.05 cycles/h) and with a large amplitude (Rd mean = 248 mg/min; peak-to-peak amplitude = 85 mg/min). Direct splanchnic balance measurements were made in the interval 240-540 min to determine the specific contributions of splanchnic (Rds) and peripheral glucose uptake (Rdp) to the oscillation in total Rd. Peripheral uptake oscillated in phase with plasma insulin and accounted for 80% (57.5 g) of total Rd. The splanchnic bed (presumably liver) sequestered 20% (14.1 g) of infused glucose, and Rds varied in phase with plasma glucose. The liver extracted 5.6 +/- 0.3% of the total amount of glucose presented to it in the 5-h interval of observation. It is concluded that a) large fluctuations in peripheral glucose utilization are responsible for the observed periodicities in glucose concentration; b) peripheral uptake fluctuations result from periodic bursts in insulin secretion; c) during glucose infusion, glucose is the primary moment-to-moment regulator of hepatic glucose uptake, whereas insulin is the principal regulator of peripheral glucose utilization.

Animals↗
PubMed1980

How descending limb of Henle's loop permeability affects hypertonic urine formation.

An isomorphic, dynamic model of the antidiuretic medulla and distal tubule was used to determine how vasa recta (VR) plasma flow and the nature of descending limb (DLH) equilibration influences inner medullary urine concentrating ability in the steady state. Four DLH modes were examined: water recycling with limited solute permeability, ideal water recycling, mixed water-solute recycling, and strict solute recycling. Each DLH mode was evaluated with and without thin ascending limb (tALH) NaCl active transport. Results indicate that VR plasma flow strongly affects medullary solute accumulation, that NaCl reabsorption from passive tALH is insufficient to establish a positive corticomedullary NaCl gradient, that even limited DLH solute entry compromises the medulla's ability to establish an axial osmotic gradient without active transport, and that with tALH active NaCl transport, positive inner medullary NaCl and osmotic gradients could be established with all four DLH modes. We conclude that tALH NaCl active transport or some other form of osmotic work must be invoked to account quantitatively for inner medullary concentrating effects in rodents.

Animals↗