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Biomedical subjects

M W Smith

Publications and source records attributed to M W Smith.

At least 307 records · Page 17Linked to original sources
PubMed1976

Positional and species analysis of membrane phospholipids extracted from goldfish adapted to different environmental temperatures.

1. The proportion of ethanolamine phosphoglycerides in microsomal fractions of goldfish intestine increases at low environmental temperatures. The fatty acyl composition also changes, the proportion of C22:6 and C20:4 fatty acids increasing in positions 1 and 2 and position 2 respectively. The proportion of C16:0 and C18:0 fatty acids falls in position 1 and there is an apparent switch of C18:1 and C20:1 fatty acids from position 2 to position 1. 2. The proportion of choline phosphoglycerides does not depend on the previous environmental temperature of the fish. Temperature-dependent changes in fatty acyl composition in positions 1 and 2 take place in a way similar to that described for ethanolamine phosphoglycerides, but in this case C22:6 substitution is confined to position 2. 3. Choline phosphoglycerides have been further separated into 7 different molecular species. The amounts of species 3 to 7 increase and the amount of species 2 decreases at low adaptation temperature. These changes only account for part of total change in fatty acyl composition. The remaining changes occur by chain substitution within species. 4. Present results show temperature adaptation to be highly complex, involving both quantitative and qualitative changes in different phospholipids. The possible physiological significance of these changes are discussed together with the effects these changes might have on cholesterol-phospholipid interactions.

Acclimatization↗
PubMed1976

Amino acid transport by the helicoidal colon of the new-born pig.

The proximal colon of the new-born pig maintains a stable short-circuit current which is partly dependent upon the presence of methionine. This interaction betweeen methionine and short-circuit current shows Michaelis-Menten knetics with a Km of 0.24 mM and a V of 27 muA.cm-2. The net flux of methionine to the serosal surface of proximal colons also shows a hyperbolic relation to the external concentration of methionine (Km 0.38 mM; V 10.4 nmol.cm-2. min-1). The proximal colon concentrates methionine within its epithelium giving a mucosal to medium ratio of 11.2 +/- 1.9 (90 min incubation in 1 mM methionine). The ability of the colon to transport methionine across and concentrate methionine within its mucosa is maintained for at least 24 h after birth. Colonic transport of amino acids could be physiologically important in the pig, where the immediate post-natal transfer of immune globulins has been shown to cause a temporary inhibition of normal intestinal function.

Animals↗
PubMed1976

Methionine transport by pig colonic mucosa measured during early post-natal development.

New-born pig proximal colon, incubated in vitro, transports methionine with a Km of 0-33 mM and a Vmax of 0-62 mumole cm-2h-1. There is still a net transport of methionine on day 4, but the Km now increases to 10 mM and the Vmax falls to 0-15 mumole cm-2h-1. There is no net transport of methionine across proximal colons taken from 10-day-old pigs. 2. The mean intramucosal concentration of methionine, following incubation in medium containing 1 mM methionine, is 7-18+/-0-8 mM for the new-born, 0-55+/-0-05 mM for the 4-day-old and 0-31+/-0-06 mM for the 10-day-old pig. 3. Both methionine and glucose cause an immediate increase in the short-circuit current of new-born and 1-day-old pig colons. The kinetics for this interaction with methionine gives a Km for methionine of 0-24 mM and a maximum effect of 27 muA cm-2. This effect is not seen in 4- or 10-day-old pigs. 4. Net Na+ transport across the new-born pig proximal colon, measured in the absence of methionine, is about three times that calculated from the measured short-circuit current. Methionine increases the mucosal to serosal flux of Na+ by an amount roughly equal to that predicted from the increase in short-circuit current. The ability of glucose and methionine to affect short-circuit current is lost by day 4. 5. Short-circuit current, measured in the absence of methionine or glucose, increases between day 1 and 2 of post-natal life. This increased electrogenicity is maintained for up to at least 10 days after birth. 6. The pig proximal colon has many of the properties of a small intestine at birth. It actively transports methionine and the presence of methionine stimulates the absorption of Na+. These effects could be physiologically important in the pig, where the normal absorptive function of the intestine is temporarily inhibited at birth by the intestinal transmission of immune globulins.

Age Factors↗
PubMed1976

Electrical properties of pig colonic mucosa measured during early post-natal development.

Microvillar membrane (Vm) and transmural (Vt) potential differences were measured in proximal colon taken from pigs at birth and up to 10 days of age. 2. Vm remained independent of the age of the animal provided it was measured in the absence of methionine. The over-all mean was -43-3 mV. Adding methionine to fluid bathing the mucosal surface of new-born pig colon caused a 9-8 mV depolarization of Vm and a 6-7 mV increase in Vt. These effects, which were Na+-dependent, were not seen in the 10-day-old animal. 3. Substituting SO4(2-) for Cl- in methionine-free medium caused a hyperpolarization in Vm. Increasing the concentration of K+ caused corresponding depolarization. Substituting choline for Na+ had no effect on VmCl- and K+ movement across the microvillar membrane together account for the bulk of the measured membrane potential. These results apply to all stages of development. 4. Na+ uptake across the microvillar membrane of the new-born pig colon was increased in the presence of methionine. This effect disappeared in older animals. Na+ uptake in the absence of methionine doubled during the first 24 h of post-natal life. This increase was maintained using colons taken from older animals. 5. Methionine depolarization of Vm in the new-born pig colon is probably caused by the electrogenic influx of Na+. The ability of the colon to actively concentrate methionine within tis mucosa disappears at the same time as methionine ceases to affect Vm and Vt. It is suggested that methionine and Na+ form a ternary complex with a carrier in the brush border of the new-born pig colon and that this carrier is lost or modified during early post-natal development.

Age Factors↗
PubMed1976

Temperature adaptation in fish.

Altering the body temperature of fish causes immediate changes in both the functional and biochemical properties of secretory epithelial tissues. The present account describes how the intestinal tract of the goldfish adapts to regulate its function after a sudden exposure to a change in environmental temperature. Adaptation can be seen to take place in three distinct steps. The first stage, occurring 15-20h after the change in environmental temperature, alters the ability of actively transported non-electrolytes to increase the microvillar membrane permeability to sodium. The passive permeability of the cells to sodium is also regulated at this stage. The second adaptive change involves changes in membrane phospholipids and amino acid transport. This occurs after about 32-48h. Regulation is still not complete, however, the intracellular sodium remaining low and intracellular potassium remaining high for 2-3 weeks. There is then a final regulation of sodium-pump activity. This change, which is concerned with pump turnover rather than with number of pump sites, is probably connected with the synthesis of new cells. These changes are discussed in detail, and an attempt is made to relate fine changes in phospholipid fatty acyl composition to known changes in membrane function.

Adaptation, Physiological↗
PubMed1975

Sodium and chloride transport by the intestine of the European flounder Platichthys flesus adapted to fresh or sea water.

1. Everted intestinal sacs prepared from Platichthys flesus adapted to sea water (SW) have higher rates of salt and water transport than did sacs prepared from fresh water adapted (FW) fish. 2. Intestines mounted in Ussing chambers gave stable open-circuit voltages and short-circuit currents after pre-incubation for 20--30 min of --1.91 +/- 0.14 (14) mV and --45.0 +/- 5.1 (14) muA/cm2, SW fish, and --1.24 +/- 0.14 (11) mV and --18.2 +/- 3.6 (11) muA/cm2, FW fish. 3. Isotope flux measurements indicated a net Na transport of 21.5 +/- 4.1 (11) neq/cm2-min in SW fish intestines, but no significant Na transport in FW fish (7.6 +/- 7.6 (9) new/cm2-min). Both preparations showed an active Cl transport, 26.6 +/- 6.1 (12) neq/cm2-min for SW and 18.5 +/- 9.7 (17) neq/cm2-min for FW fish. 4. No significant difference in the uptake of Na or Cl across the mucosa was observed between FW and SW fish. The uptake of both ions showed some saturation at high concentrations. 5. Interactions between Na and Cl uptake were small, although Cl uptake was significantly higher in Na-free solutions. 6. It is concluded that electrogenic Cl transport may be the dominant mechanism for water and salt transport in flounder intestine, and that adaptation to a saline environment involves regulation of pumping rather than Na or Cl entry across the mucosal membrane.

Animals↗
PubMed1975

Glucose- and phlorrhizin-protected thiol groups in pig intestinal brush-border membranes.

Purified brush borders, prepared fro newborn pig intestine, were incubated in the presence of 203Hg-labelled p-chloromercuribenzenesulphonic acid and the membrane proteins later separated by polyacrylamide-gel electrophoresis. The presence of either D-glucose or phlorrhizin, during a preliminary incubation in non-radioactive p-chloromercuribenzenesulphonic acid, increased the subsequent binding of the 203Hg-labelled compound to a protein of molecular weight 31500. This increase appeared to be specific for the low-molecular-weight protein, provided that the concentration of protecting agent used corresponded to that used to produce a biological response in the intact tissue. These results are discussed in relation to the known properties of other presumptive sugar carriers isolated from different membranes.

Animals↗
PubMed1975

Some aspects of the ecology and lifecycle of Amblyomma cajennense (Fabricius 1787) in Trinidad and their influence on tick control measures.

The distribution in Trinidad of the tick Amblyomma cajennense is defined, and the methods used to determine the boundaries of the infested areas are outlined. The relationships between climate, vegetation and husbandry methods and the distribution of the tick are described. Monthly tick collections from specific animals to determine exact seasonal variations were not possible but a study was made of the normal life cycle under laboratory conditions, the results being used to assist in interpreting the field picture and formulating methods of control. Possible systems of control are outlined and mention is made of the feasibility of eradication of the species in Trinidad.

Animals↗
PubMed1975

Transport of electrolytes across the helicoidal colon of the new-born pig.

1. The Na, K, Cl and water content of faeces removed from different parts of the pig helicoidal colon were determined for 1-day-old and adult animals. Faecal Na, Cl and water content fell in both cases during passage of contents through the colon. K content increased in the distal colon of the adult pig. This did not occur in the 1-day-old animal. 2. The colon of the 1-day-old pig removed a larger proportion of water from its contents than did that of the adult. The absorption of both water and Cl was found to extend into the distal colon of the 1-day-old animal; little or no net absorption took place in this region in the adult. 3. Colons taken from new-born pigs maintained stable short-circuit currents of about 60-80 muA cm-2 with open-circuit voltages of about 10 mV. Similar values were found for proximal and mid regions of colons taken from 1-day-old, suckled animals. In the distal colon, however, both short-circuit current and open-circuit potential doubled after suckling. 4. Measurements of Na flux in vitro showed no regional difference at birth. The amount of Na absorbed, about 4.5 muequiv cm-2 h-1, was twice that predicted from the short-circuit current, supposing that to be due solely to the electrogenic transport of Na. 5. Colons taken from suckled pigs transported Na at double the rate found in the new-born animal. This applied to both the proximal region, where the short-circuit current remained constant, and the distal region, where the short-circuit was double that of the new-born. 6. Fluxes of Cl and K were also measured across the proximal colon of the one-day-old, suckled pig. There was a net absorption of Cl and secretion of K (1.3 and -0.05 muequiv cm-2 h-1 respectively). These fluxes, taken together with that for Na, could not wholly account for the short-circuit current measured across these preparations. 7. The pig colon seems well able to cope with both electrolyte and water absorption during the first 24 hr of post-natal life. Part of the absorbed sodium appears to follow a non-electrogenic, possibly pinocytotic, route, but the full ionic contribution to the measured short circuit current has still to be determined.

Animals↗
PubMed1974

Sodium transport by the small intestine of new-born and suckling pigs.

1. Sodium transport has been measured across in vitro preparations of pig ileum taken at birth or during the first 10 days of post-natal life.2. Both the unidirectional and net fluxes of sodium fell shortly after colostrum was ingested by the new-born piglet. These changes were associated with falls in short-circuit current, open-circuit voltage and tissue conductance and with the appearance of protein-filled vacuoles within the mucosal epithelium.3. Overnight fasting of piglets following a period of suckling caused all sodium fluxes to revert to values similar to those found in the new-born animal. The short-circuit current also increased on fasting but the magnitude of this effect decreased with age.4. The suckling-dependent inhibition of sodium transport was not associated with any change in the level of adenine nucleotides within the mucosa. However the rate at which sodium entered the intestinal mucosa of suckled pigs was found to be only half that of the new-born.5. It is suggested that pinocytosis might use up or chemically modify the microvillar membrane making it less permeable to sodium. Subsequent fasting would, by replenishment or further modification of existing membrane surface, allow the epithelium to recover its original permeability to sodium and possibly regain the ability to undergo a further cycle of pinocytotic activity.

Adenosine Diphosphate↗
PubMed1974

Protein and glucose-induced changes in sodium transport across the pig small intestine.

1. The effect of glucose and of bovine gamma-globulin on short-circuit current and sodium transport was measured using new-born pig ileum before and after suckling.2. Glucose increased the short-circuit current with an apparent K(m) of 1.9 and 19.5 mM for new-born unsuckled and suckled intestines respectively. The V(max) was about 80 muA cm(-2) in each case.3. Bovine gamma-globulin applied to new-born pig ileum caused a 20% increase in sodium chloride influx without change of short-circuit current. The tissue conductance was also greater in the presence of globulin. These effects were not seen in ileum taken from suckled pigs.4. p-Chloromercuriphenyl sulphonic acid (PCMPS) inhibited the globulin induced increase in sodium influx in new-born pig ileum without changing the measured short-circuit current. 0.1 mM-PCMPS also changed the characteristics of the glucose-dependent increase in short-circuit current, so that this response came to resemble that seen in ileum taken from suckled pigs. Dithioerythritol reversed this effect of PCMPS.5. The suckling-dependent difference in results is explained in terms of a change in microvillar function taking place as a consequence of long-term pinocytosis in vivo. The ability of PCMPS to simulate some of these changes suggests that sulphydryl groups might be important regulators of microvillar membrane stability.

Animals↗