IT is now generally accepted, chiefly from the work of Gaskell and Engelmann, that the different parts of the heart are of varying automaticity, and that the normal beat is due to the more rapid rhythmic contraction of the venous end of the heart, the contraction set up being propagated to the other parts in sequence. And it is known that in various circumstances the order of beat may be reversed.The work of Herlitzka, Mines, Clark and others has shown the great importance of the reaction of the fluid perfusing the heart in connexion with the origination of rhythm, while Mines (i) has pointed out that the limits of hydrogen ion concentration (CH.) within which the development of spontaneous beats is possible differ for the hearts of different kinds of animals.In experimenting with the auricle-ventricle preparation of the frog we found that this preparation would not beat spontaneously in a slightly acid Ringer's solution in which the sinus would beat regularly, but that if a small amount of Na2CO3 solution was introduced into the cannula the auricle at once started a regular, spontaneous rhythm. This observation led us to make experiments to ascertain whether there is a difference in the optimal CH. for the development of rhythm in the different chambers of the heart, and, if so, to determine the limits of CH. between which each chamber will originate spontaneous contractions.Methods. Medium-sized or large specimens of Rana temp. were used for these experiments which were carried out chiefly in the 1 A preliminary communication of this research was published in the Proc. Physiol. Soc. p. i. 1913 (this Journal, XLVII.).
An ammonium picket porphyrin that targets bacterial membranes has been prepared and shown to bind to phosphatidylglycerol (PG), a bacterial lipid, when the lipid was in solution, contained within synthetic membrane vesicles, or when in Gram-negative and Gram-positive bacterial membranes. The multifunctional receptor was designed to interact with both the phosphate anion portion and neutral glycerol portion of the lipid headgroup. The receptor's affinity and selectivity for binding to surfactant vesicles or lipid vesicles that contain PG within their membranes was directly measured using fluorescence correlation spectroscopy (FCS). FCS demonstrated that the picket porphyrin's binding pocket was complementary for the lipid headgroup, since simple Coulombic interactions alone did not induce binding. (1)H NMR and isothermal titration calorimetry (ITC) were used to determine the receptor's binding stoichiometry, receptor-lipid complex structure, binding constant, and associated thermodynamic properties of complexation in solution. The lipid-receptor binding motif in solution was shown to mirror the binding motif of membrane-bound PG and receptor. Cell lysis assays with E. coli (Gram-negative) and Bacillus thuringiensis (Gram-positive) probed with UV/Visible spectrophotometry indicated that the receptor was able to penetrate either bacterial cell wall and to bind to the bacterial inner membrane.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.