Nonuniform effects of histamine on small pulmonary vessels in cats

In in vivo cat lung, using an X-ray TV system, we analyzed responses in internal diameter (ID), flow velocity, and volume flow of arteries and veins (100-500 microns ID) to histamine (8-15 micrograms/kg iv) under three conditions. With histamine alone, three types of ID response (constriction, dilatation, and no change) occurred in parallel-arranged arteries. Relative frequency and magnitude of constriction were maximum in arteries of 300-400 micron ID, whereas those of dilatation were maximum in arteries of 100-200 micron ID. In veins, relatively uniform constriction occurred. Under H2-blockade, histamine caused greater constriction than that with histamine alone in arteries and veins of 300-500 micron ID. Under beta-blockade, with histamine, ID of all vessels decreased significantly below the ID sizes under the above two conditions, and no dilatation occurred. In two parallel arteries that showed opposite ID changes to histamine, flow velocity increased, but volume flow decreased in a constricted artery while it increased in a dilated one. Those data indicated that, with histamine, qualitatively and quantitatively nonuniform ID response was induced in both parallel- and series-arranged small pulmonary arteries and, in turn, produced heterogeneous flow distribution. Factors to cause the nonuniformity may be partly explained by difference in density of H2- and beta-receptors in vascular walls.     

Vagally and acetylcholine-mediated constriction in small pulmonary vessels of rabbits

Using a new X-ray TV system, we analyzed effects of vagal nerve stimulation (VNS; 1-30 Hz) and intravenous injection of acetylcholine (Ach; 0.3-0.9 microgram) on the internal diameter (ID; 100-1,500 microns) of small pulmonary arteries and veins in anesthetized rabbits. In selective segments of the arteries, ID decreased abruptly and maximally by 50-70% in a specific stimulus frequency to the vagal nerve and a dose of ACh. The vasoconstrictor sites were distributed near the branching points of the arteries, particularly those downstream, and their numbers increased with an increase in the stimulus frequencies and ACh doses. The relative frequencies of occurrences were 15.3% with VNS (30 Hz) and 5.3% with ACh (0.9 microgram). In nonselective segments with VNS, ID decreased frequency dependently by 0, 4, 12, and 26% at 1, 4, 15, and 30 Hz, respectively, and with ACh, decreased dose dependently by 21 and 35% with 0.3 and 0.9 microgram, respectively. The vasoconstriction in response to VNS and ACh was attenuated by atropine, enhanced by eserine, and not affected by phentolamine. That vasoconstriction to VNS was abolished by hexamethonium. No selective constriction was found in veins and the ID was decreased uniformly by 1-2% with VNS and ACh.     

Improvement of proteolytic resistance of immunoadsorbents by chemical modification with polyethylene glycol

Immunoadsorbents were modified with monomethoxy-polyethylene glycol (PEG; average molecular weights of 5000 (PEG-5000) and 1900 (PEG-1900)) activated with cyanuric acid (activated PEG) by four different methods. In the two methods, anti-BSA antibodies were modified with activated PEG with and without protection of antigen binding sites with BSA and then were coupled to CNBr-activated Sepharose 4B. In the other two methods, Immunoadsorbents, which were prepared by coupling anti-BSA antibodies to CNBr-activated Sepharose 4B, were modified with activated PEG with and without the protection. The effects of PEG modification by these four methods on the binding ratio (the ratio of the numbers of moles of antigen adsorbed to the numbers of moles of binding sites of antibody coupled), the antigen binding property and the resistance to proteolytic digestion of immunoadsorbents were studied. The decrease in the binding ratio by the modification with activated PEG was small enough to use modified immunoadsorbents for industrial purification processes. The resistance to proteolytic digestion of immunoadsorbents was improved by modification with activated PEG. The modification without protection of antigen binding sites gave higher resistance to proteolytic digestion than that with protection, while the former caused larger decrease in the binding ratio of modification. The immunoadsorbents modified with activated PEG-5000 showed higher resistance to proteolytic digestion than those modified with activated PEG-1900.     

Measurement of enzyme reaction rates using advanced pH control system: application of repetitive PF system

The aim of this article is to develop the on-line measurement system of enzyme reaction rates, using an advanced pH controller, which is called a repetitive PF(Programmed Controller/Feedback Compensator) System. In the esterolysis reaction of the N-acetyltyrosine ethyl ester by alpha-chymotrypsin, the enzyme reaction rate could be calculated from the amount of base required for keeping the pH constant. The proposed controller has a learning mechanism in which the knowledge is obtained from the former results of the repetition, and pH was controlled much more successfully by the proposed repetitive PF System than by the conventional on-off controller, PI controller, and the adaptive controller. The enzyme reaction rate could be evaluated each time as accurately as possible based on the result of the controlled batch reaction. Using Lineweaver-Burk plots of the estimated reaction rates, kinetic parameters, such as the enzyme activity and Michaelis-Menten constant, could be estimated more accurately and from fewer experiments by the repetitive PF system than by initial reaction rates using on-off pH-stat.     

Characterization of fractionated polyclonal antibodies for immunoaffinity chromatography

Polyclonal anti-BSA antibodies were ractionated by stepwise elution from an immobilized BSA column by decreasing pH or increasing the concentration of NaSCN. The binding affinities of each fraction and original globulin under physiological conditions and their dependence on pH and ionic environments were compared. Fractions with high association constant under physiological conditions did not necessarily show antigen binding affinity over a wide pH range, but they retained a high affinity at higher ionic strength of NaSCN. Consequently, by combining these two fractionation procedures, a fraction with high affinity and which dissociated at moderate pH was obtained. It is clear that high affinity is not always incompatible with ease of dissociation accompanying a change in conditions.     

Regulation of the slow Ca++ channels of myocardial cells

Contraction of the heart is regulated by a number of mechanisms, such as neurotransmitters, hormones, autacoids, pH, intracellular ATP, and Ca⁺⁺ ions. These actions are mediated, at least in part, by actions on the sarcolemmal slow (L-type) Ca⁺⁺ channels, exerted directly or indirectly. The major mechanisms for the regulation of the slow Ca⁺⁺ channels of myocardial cells includes the following. cAMP/PK-A phosphorylation stimulates the slow Ca` channel activity, whereas cGMP/PK-G phosphorylation inhibits. DAG/PK-C phosphorylation and tyrosine kinase phosphorylation are suggested to stimulate the slow Ca⁺⁺ channel activity. Intracellular application of G_s protein increases the slow Ca⁺⁺ currents (ICa(L)). Lowering of intracellular ATP inhibits I_Ca(L). Acidosis and increase in [Ca]_i inhibits I_Ca(L). A number of changes in the Ca⁺⁺ channels also occur during development and aging. Thus, it appears that the slow Ca⁺⁺ channel is a complex structure, including perhaps several associated regulatory proteins, which can be regulated by a number of extrinsic and intrinsic factors, and thereby control can be exercised over the force of contraction of the heart.     

Thromboxane A2/endoperoxide receptors mediate cholinergic constriction of rabbit lung microvessels.

Using an X-ray television system, we directly measured the internal diameter (ID; 100-1,000 microns) of small pulmonary arteries and analyzed the effects of cyclooxygenase inhibition and thromboxane A2/prostaglandin endoperoxide (TP) receptor blockade on the ID reductions in response to vagal nerve stimulation (VNS; 16 Hz) and injection of acetylcholine (ACh; 0.3 micrograms) in anesthetized rabbits. The ID reductions of the small arteries in response to VNS and ACh were completely abolished by pretreatment with cyclooxygenase inhibitors indomethacin and meclofenamate. Those reductions were also eliminated by pretreatment with TP receptor antagonists AA-2414 and Ono 3708. Both TP receptor antagonists abolished the ID reduction to thromboxane A2 mimetic U-46619 but did not affect the reduction to norepinephrine. The ID reductions in response to VNS and ACh were eliminated by atropine. The reduction in response to VNS was abolished by hexamethonium bromide, whereas the reduction in response to ACh was not altered by hexamethonium bromide. The results indicate that vasoconstrictions of the rabbit small pulmonary arteries in response to VNS and exogenous ACh are mediated by TP receptors as well as muscarinic receptors. The data suggest that during VNS endogenous ACh acts on muscarinic receptors to constrict the small arteries mainly by generating thromboxane A2 or prostaglandin endoperoxide.     

Diffusive and hydraulic transfer of solutes through homogeneous membranes

Rates of hydraulic transport of water, solute permeabilities, and sieving coefficients of homogeneous kappa-carrageenan and bovine serum albumin membranes were measured. These values increased with the water content of membranes. The data show good agreement with the predictions based on the pore model.