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Biomedical subjects

G B Weiss

Publications and source records attributed to G B Weiss.

At least 91 records · Page 5Linked to original sources
PubMed1980

Effects of stimulatory agents on mobilization of high and low affinity site 45Ca in rabbit aortic smooth muscle.

The relationships between contractile responses to stimulatory agents and changes in binding and distribution of La+++-resistant Ca++ at kinetically distinct high and low affinity sites were investigated. The magnitude of the norepinephrine (NE)-induced decrease in 45Ca retention (associated with release of high affinity Ca++) after exposure to La+++ and low temperature was similar when NE was present either for the entire 45Ca incubation period (40--120 min) or for as short an interval as the final minute of the incubation period. Under conditions favoring high affinity binding of Ca++, uptake of 45Ca was slow (T 1/2 approximately equal to 30 min) but the NE-induced decrease in 45Ca retention was rapid. Conversely, low affinity Ca++ sites load rapidly (T 1/2 less than or equal to 5 min) retain increased 45Ca in the presence of elevated (160 mM) K+ at all incubation intervals (5--120 min) and accumulate even more 45Ca in proportion to the increase in contraction obtained when NE is also present either for the entire incubation period or for only the final portion (1 min or longer). Similar effects on both high and low affinity binding of Ca++ are obtained with equipotent concentrations of NE and histamine. Simultaneous application of NE and histamine did not alter high and low affinity binding of Ca++ significantly more than did separate administration of either agent. These results indicate that NE and histamine effect similar high and low affinity Ca++ sites and that, even though equilibrium of Ca++ with high affinity sites is a much slower process than with low affinity sites, stimulatory agents can elicit rapid changes in the amount of Ca++ present at either site.

Animals↗
PubMed1980

Dissociation of varied actions of norepinephrine on 45Ca uptake and release at different sites in rabbit aortic smooth muscle.

The basis for different observed effects of norepinephrine (NE) on 45Ca fluxes was investigated by characterizing changes in binding of various distinct Ca++ fractions. The presence of a sufficiently high concentration of Sr++ (5.0 mM) prevents 45Ca uptake at high affinity Ca++ binding sites, whereas that at low affinity Ca++ binding sites is unaffected. Addition of Sr++ after equilibration with 45Ca also specifically displaces high affinity 45Ca. Efflux of 45Ca is increased by 10(-6) M NE when muscles are washed out with 1.5 mM Ca++ solution and decreased by NE when washed out in a O-Ca plus 0.05 mM EDTA solution. NE releases a portion (approximately 20 nmol/g of tissue) of the La+++-resistant high affinity Ca++, decreases La+++-sensitive high affinity Ca++ efflux, increases La+++-sensitive low affinity Ca++ efflux and increases La+++-inaccessible low affinity Ca++ uptake in muscles previously depolarized with a 160 mM K+-substituted solution. Of these four differing actions, Sr++ only affects the first two by preventing high affinity Ca++ binding (including that fraction of Ca++ released by NE). The interrelationships that exist between these Ca++ components are not clear, but the use of combinations of Sr++, La+++ and varied Ca++ concentrations can establish conditions under which a specific type of Ca++ binding predominates. Correlations between mobilization of specific Ca++ fractions and contractile responsiveness in vascular smooth muscle can then be examined.

Animals↗
PubMed1979

Utilization of mismatched initiator termini by avian myeloblastosis virus DNA polymerase.

DNA synthesis by avian myeloblastosis virus was studied using poly(C) as template and modified oligo(dG) as primer. The addition of one noncomplementary base to the 3'-end of the primer has no important effect on synthesis. The mispaired base is incorporated into the product and the apparent Km (for primer) and the V of the reaction remain unchanged. This confirms the absence of a 3' leads to 5'-exodeoxynuclease activity using a template that is transcribed faithfully rather than one that can undergo a slippage reaction.

Avian Leukosis Virus↗
PubMed1979

Traumatic cardiac hemolytic anemia: a late complication of a Starr-Edwards mitral valve prosthesis.

Severe, traumatic, cardiac, hemolytic anemia developed in a patient nine years after mitral valve replacement with a Starr-Edwards model 6120 prosthesis. Cardiac catheterization failed to demonstrate a perivalvular leak or prosthetic malfunction. Transfusion on two occasions resulted in accelerated hemolysis and failed to maintain an appreciable elevation of the hemoglobin level. At operation, a perivalvular leak was found. Replacement of the valve led to complete resolution of the hemolytic problem. The case demonstrates that cardiac hemolysis may be a good indicator of valve dysfunction.

Anemia, Hemolytic↗
PubMed1979

Correlation between response to norepinephrine and removal of 45Ca from high-affinity binding sites by extracellular EDTA in rabbit aortic smooth muscle.

Divalent ion chelators (EDTA, EGTA) were found to remove 45Ca from high-affinity binding sites in isolated rabbit aortic smooth muscle in a concentration-dependent manner. Measurement of 14C-labeled EDTA uptake (10 to 60-min incubation periods) yielded tissue/medium ratios equivalent to the extracellular space [14C]-sucrose tissue/medium ratio). Addition of high EDTA concentrations (0.5--1.5 mM) elicits large but reversible increases in 45Ca efflux, rapidly removes virtually all 45Ca from muscles previously incubated with 45Ca for as short a time as 7 min (filling of extracellular and superficial sites) or as long as 180 min (more complete equilibration of 45Ca), and blocks the norepinephrine-induced contractile response (this response is only partially inhibited by 0.05 mM EDTA, a concentration too low to remove most of the 45Ca present). Furthermore, phosphatidyl serine, a compound known to decrease exchangeability of 45Ca in this tissue, inhibits the EDTA-induced increase in 45Ca loss. Thus, those slowly depleted Ca++ stores that are important for the contractile action of norepinephrine are removed by EDTA even though this chelator is confined to the extracellular space. Possibly, release or removal of high-affinity Ca++ is regulated by EDTA-accessible Ca++ bound at relatively superficial membrane sites.

Animals↗
PubMed1979

Differing actions of nitroprusside and D-600 on tension and 45Ca fluxes in canine renal arteries.

Administration of nitroprusside (NP) subsequent to induction of contraction in canine renal arterial strips with norepinephrine (NE) yielded a dose-dependent relaxation and with 80 mM potassium (KCl) yielded only a small degree of relaxation. The effect elicited with 0.1 mM NP was significantly greater for responses obtained with NE (68%) than for those with KCl (12%). However, responses of muscles pretreated for 5 min with NP to NE to KCl were reduced by 23 and 31%, respectively. The relaxant effect of NP persisted after incubation with D-600 and/or 30 min of a 0-Ca plus 0.05 mM EDTA solution (low EDTA). Neither D-600 nor NP altered 45Ca uptake in the absence of stimulatory agents. Efflux of 45Ca (into low EDTA solution) was decreased by NP in a maintained manner but was unaffected by D-600. The NE-induced decrease in 45Ca efflux (but not that with KCl) was blocked by NP. However, changes in 45Ca efflux elicited with KCl or NE were not affected by D-600. In contrast to D-600 (which is known to inhibit increased Ca++ entry associated with some stimulatory conditions), NP acts in a manner that is relatively independent of uptake of extracellular Ca++. Thus, these two vasodilators appear to affect Ca++ utilization by different mechanisms and, presumably, in an additive manner.

Animals↗
PubMed1978

Inhibition of 45Ca movements by lowered temperature or lanthanum in rat brain slices.

Different components of 45Ca movements in rat cortex, striatum and hypothalamus slices were delineated by conditions and ions which selectively alter Ca2+ uptake, binding or extrusion. Equilibration of 45Ca was qualitatively similar in all three tissues and was attained within 30--60 min. The 45Ca tissue-medium ratios obtained in 1.5 mM Ca2+ solutions were increased 15--30% in 0.1 mM Ca2+ solutions and doubled in 0-Ca solutions. Efflux of 45Ca from slices can be described in terms of two components. Lowering the temperature to 0 degree C increased 45Ca uptake into the slower washout component and markedly decreased 45Ca efflux. Exposure to 1.5 mM La3+ decreased both 45Ca uptake and efflux. The inhibitory effects of 0 degree C and La3+ on 45Ca efflux were additive. Uptake of 45Ca in slices incubated in 1.5 mM Sr 2+-substituted (0-Ca) solutions was more similar to that in 0-Ca solutions than in 1.5 mM Ca2+ solutions. Thus, Ca2+ distribution is qualitatively similar in slices from different rat brain areas, loss of 45Ca is an energy dependent process which is at least partially coupled to Ca2+ uptake, decreased temperature inhibits Ca2+ extrusion, La3+ impedes uptake and subsequent binding of Ca2+, and Sr2+ does not prevent the major portion of 45Ca uptake at cellular binding sites. Use of 0 degree C and La3+ to inhibit discrete components of Ca2+ fluxes in rat brain area slices provides a basis for investigation of the mechanisms by which other agents can alter Ca2+ distribution in the central nervous system.

Animals↗
PubMed1978

Effects of norepinephrine, dopamine and potassium on tension and 45Ca fluxes in canine and rabbit renal arteries.

The action and interactions of three vasoconstrictors, norepinephrine (NE), dopamine (DA) and elevated potassium ion (K+) on contractile responses and associated 45Ca movements were investigated in isolated rabbit and canine renal arteries (RA). Dose-response curves indicate that NE is 39 times more potent than DA in canine RA and 122 times more potent in rabbit RA. Prior exposure to 80 mM K+ did not prevent contractile responses to NE or DA but, conversely, K+ -induced responses did not occur after exposure to NE or DA. Responses to NE persisted after maximum DA-induced contractions but only a small response to DA was observed after a maximum NE-induced contraction. After 30 to 60 min in either a O-Ca or a O-Ca plus 0.05 mM EDTA solution, contractile responses were differentially inhibited (K+ more than DA more than NE). Efflux of 45Ca into a O-Ca plus EDTA solution was qualitatively similar in canine and rabbit RA. Addition of K+, DA or NE decreased the rate of 45Ca efflux in both RA; phentolamine abolished the NE-induced decrease and had no effect on the K+-induced decrease. The observed decrease in 45Ca efflux may reflect an inward shift of 45Ca from membrane binding sites. The mechanisms by which this effect is obtained appear to differ for K+, DA and NE. The differing actions of NE and DA cannot be explained solely by variations in potency at a singel type of receptor.

Animals↗