Showing papers on "Toad published in 1999"

What role for membranes in determining the higher sodium pump molecular activity of mammals compared to ectotherms

Abstract: The major body organs of mammals have sodium pumps that turn over energy (ATP) three to four times faster than those of ectotherms, at the same temperature. To examine if membranes play a role in these differences in molecular activity, membrane cross-over experiments were performed using two representative species, Rattus norvegicus and Bufo marinus. Microsomal membrane of kidney and brain displayed characteristic molecular activity differences (three- to four-fold) between the species. These molecular activity differences could be removed by delipidation. Pre-existing molecular activities and differences could be restored when reconstituted with original membrane. Using the same reconstitution method, species membrane cross-over experiments resulted in toad sodium pumps in rat membrane significantly increasing (≈30–40%) and rat sodium pumps in toad membrane significantly decreasing (≈40%) activities in both kidney and brain. Analysis of membrane composition showed reduced cholesterol content and differences in the fatty acids of phospholipids with higher overall unsaturation in the mammal. The scope for membranes to determine protein performance and its broader implications for metabolism are discussed.

Pharmacological and biochemical investigation of receptors for the toad gut tachykinin peptide, bufokinin, in its species of origin.

Abstract: This is the first report of the development of a new radioligand [125I]Bolton-Hunter bufokinin ([125I]BH-bufokinin) and its use in the characterisation of tachykinin receptors in the small intestine of the cane toad, Bufo marinus. The binding of [125I]BH-bufokinin to toad intestinal membranes was rapid, saturable, of high affinity and to a single population of binding sites with KD 0.57 nM and Bmax 3.1 fmol mg wet weight tissue—1. The rank order of affinity of tachykinins to compete for [125I]-BH bufokinin binding revealed similarities with that of the mammalian NK1 receptor, being bufokinin (IC50, 1.7 nM)>physalaemin (6.7 nM)>substance P (SP, 10.7 nM)≥neuropeptide γ (NPγ, 12.4 nM)≥kassinin (17.8 nM)>scyliorhinin I (35.3 nM)≥eledoisin (40.6 nM)≥carassin (43.2 nM)≥neurokinin A (NKA, 57.8 nM)≥neurokinin B (NKB, 77.5 nM)>>scyliorhinin II (338 nM). The mammalian NK3-selective agonist senktide was a very weak competitor. The radioligand [125I]neurokinin A showed no specific binding to toad intestinal membranes. In the toad isolated small intestine, the maximum contractile response to bufokinin was over 150% greater than that to acetylcholine in longitudinal muscle, whereas responses to bufokinin and acetylcholine were similar in circular muscle. Bufokinin was the most potent agonist (EC50 0.34 nM) and produced a long-lasting contraction. Other tachykinins such as physalaemin, SP and kassinin were also potent contractile agents. The potency values of mammalian and amphibian tachykinins derived from functional studies (pD2) correlated significantly with those from binding assays (pKi). The data for fish and molluscan tachykinins, however, showed poor correlation. Contractions to bufokinin and SP were unaffected by atropine, indomethacin and tetrodotoxin. The highly selective NK1 receptor antagonists CP 99994, GR 82334 and RP 67580 were ineffective in both binding and functional studies. Bufokinin increased inositol monophosphate formation in a concentration-dependent manner with an EC50 value of 10.7 nM, suggesting that the tachykinin receptor may be coupled to phosphoinositol hydrolysis. In summary, this study provides evidence for a high-affinity, bufokinin-preferring, NK1-like tachykinin receptor in the toad small intestine. This is probably not the receptor which mediates contraction to carassin, scyliorhinin II and eledoisin. The study also provides evidence that bufokinin and its receptor play an important physiological role in regulating intestinal motility.

An electrophoretic study of myosin heavy chain expression in skeletal muscles of the toad Bufo marinus.

Abstract: In this study we developed an SDS-PAGE protocol which for the first time separates effectively all myosin heavy chain (MHC) isoforms expected to be expressed in iliofibularis (IF), pyriformis (PYR), cruralis (CRU) and sartorius (SAR) muscles of the toad Bufo marinus on the basis of previously reported fibre type composition. The main feature of the method is the use of alanine instead of glycine both in the separating gel and in the running buffer. The correlation between the MHC isoform composition of IF, SAR and PYR muscles determined in this study and the previously reported fibre type composition of IF and SAR muscles in the toad and of PYR muscle in the frog was used to tentatively identify the MHC isoforms expressed by twitch fibre types 1, 2 and 3 and by tonic fibres. The alanine-SDS electrophoretic method was employed to examine changes in the MHC composition of IF, PYR, CRU and SAR muscles with the ontogenetic growth of the toad from post-natal life (body weight < 1 g) to late adulthood (body weight 200–450 g). The developmental changes in the MHC isoform composition of the toad IF muscle observed in this study are in very good agreement with those in the fibre type composition of the developing IF muscle reported in the literature.

Direct effects of lithium chloride on the activities of delta 5-3 beta and 17 beta-hydroxysteroid dehydrogenase in the testis and Bidder's organ of the adult toad (Bufo melanostictus)--in vitro study.

Abstract: Steroidogenic key enzymes, i.e. delta 5-3 beta and 17 beta-hydroxysteroid dehydrogenase (delta 5-3 beta and 17 beta-HSD) activities, in the testis and Bidder's organ of the toad were inhibited and ascorbic acid synthesis in these organs was decreased by a wide range of lithium concentration in in vitro study. A significant inhibition was noted at a concentration of 2.0 mM, which is easily achieved in the blood during the treatment of manic patients by lithium chloride. This experiment reflected that lithium exerts a direct inhibitory effect on hydroxysteroid dehydrogenase activities in the testis and Bidder's organ--a rudimentary ovary in Bufo.

The Natriuretic Peptides and their Receptors in the Brain of the Amphibian, Bufo marinus

Abstract: Examines the brain natriuretic peptide system of the toad, Bufo marinus. The data show that the toad brain contains an extensive natriuretic peptide system that could possibly interact with peptides such as arginine vasotocin and several other hormones involved in a number of different functions. The data also indicate natriuretic peptides in the toad brain may exert their efforts via both guanylate cyclase and non-guanylate cyclase containing receptors.