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Biomedical subjects

R C Thomas

Publications and source records attributed to R C Thomas.

At least 91 records · Page 5Linked to original sources
PubMed1978

Comparison of the mechanisms controlling intracellular pH and sodium in snail neurones.

Ion-sensitive microelectrodes were used to record intracellular pH, Na+ and Cl- in snail neurones. NaCl or HCl was injected iontophoretically to compare the Na pump with the pHi regulating system. The Na pump was inhibited by ouabain, carbonyl cyanide m-chlorophenyl hydrazone and increasing the membrane potential, whereas the pHi regulating system was relatively unaffected. Activation of the Na pump had no effect on pHi whereas activation of the pHi recovery process increased internal Na+. Activation of the pHi recovery process by CO2 application increased internal Na+ and also decreased internal Cl-. The results show that there is no direct connexion between the Na pump and the pHi recovery process, and that the pHi recovery process is electroneutral, and appears not to require metabolic energy. The results also confirm that the pHi recovery process involves the influx of Na+ ions and the efflux of Cl- ions.

Acid-Base Equilibrium↗
PubMed1978

Metabolic fate of tolazamide in man and in the rat.

The metabolic fate of tolazamide, 1-(hexahydroazepin-1-yl)-3-p-tolylsulfonylurea (1), was studied in man and in the rat using tritium-labeled 1. The metabolites were isolated in crystalline form from urine for structure determination. The crystal structure and final molecular structure of one of these, 1-(4-hydroxyhexahydroazepin-1-yl)-3-p-tolylsulfonylurea (5), were determined using single-crystal X-ray techniques. Following oral administration of tritiated tolazamide to male humans, 85% of the radioactivity was excreted in urine during a 5-day period. In addition to being excreted in urine unchanged, tolazamide was metabolized to 1-(hexahydroazepin-1-yl)-3-p-(carboxyphenyl)sulfonylurea (2), p-toluenesulfonamide (3), 1-(hexahydroazepin-1-yl)-3-p-(hydroxymethylphenyl)sulfonylurea (4), 1-(4-hydroxyhexahydroazepin-1-yl)-3-p-tolylsulfonylurea (5) and a labile, unidentified metabolite 6 by man. The relative amounts of these materials excreted in 0-24-h urine collections from eight subjects averaged 7, 17, 26, 10, 25, and 15% for 1-6, respectively. In the female rat, 79% of an orally administered dose of tritiated tolazamide was excreted in urine during a 5-day period as 1-4. The relative amounts of these materials excreted during the 24-h period following administration of tolazamide were 10, 5, 5, and 80% for 1-4, respectively.

Animals↗
PubMed1977

The effect of calcium injection on the intracellular sodium and pH of snail neurones.

1. Ion-sensitive glass micro-electrodes were used to measure the intracellular pH (pHi) and the intracellular sodium ion concentration, [Na+]i, in identified Helix aspersa neurones. 2. The injection of small volumes of 0-1 McaCl2, which increased the membrane potential by 10-15 mV for 1-2 min, had little or no effect on [Na+]i. Increases of up to 1 mM in [Na+]i could be reversibly induced by larger injections. 3. Calcium injection caused an immediate decrease in pHi, which appeared to be directly proportional to the amount of calcium injected. Injections causing hyperpolarizations of 10-20 mV which recovered in 2-5 min caused pHi decreases of 0-04-0-15 units. After each of these injections both pHi and the membrane potential recovered exponentially but with different time constants. 4. The injection of calcium at a low rate could decrease pHi without affecting the membrane potential. 5. Neither membrane potential nor pHi were affected by the injection of small volumes of 0-1 M-MgCl2, Injection of CoCl2 produced a large transient decrease in pHi but no significant change in membrane potential. 6. Exposure of the cell to saline equilibrated with 2-5% CO2 greatly reduced the pHi decrease caused by calcium injection but had only small effects on the membrane potential response. 7. It is concluded that most of the injected calcium is exchanged for protons inside the cell.

Animals↗
PubMed1977

An investigation of the ionic mechanism of intracellular pH regulation in mouse soleus muscle fibres.

1. Intracellular pH (pH(i)) of surface fibres of the mouse soleus muscle was measured in vitro by recessed-tip pH-sensitive micro-electrodes. pH(i) was displaced in an acid direction by removal of external (NH(4))(2)SO(4) after a short exposure, and the mechanism of recovery from this acidification was investigated.2. Removal of external K caused a very slow acidification (probably due to the decreasing Na gradient) but had no effect on the rate of pH(i) recovery following acidification. This indicates that K(+)-H(+) exchange is not involved in the pH(i) regulating system.3. Short applications of 10(-4)M ouabain had no obvious effect on pH(i) and did not alter the rate of pH(i) recovery following acidification. This suggests that there is no direct connexion between the regulation of pH(i) and the Na pump.4. Reduction of external Ca from 10 to 1 mM caused a transient fall in pH(i), but the rate of pH(i) recovery following acidification was unaffected. This suggests that Ca(2+)-H(+) exchange is not involved in the pH(i) regulating system.5. An 11% reduction in external Na caused a significant slowing of pH(i) recovery following acidification. 90% or complete removal of external Na almost stopped pH(i) recovery. This suggests that Na(+)-H(+) exchange is involved in pH(i) regulation.6. Amiloride (10(-4)M) reversibly reduced the rate of pH(i) recovery to much the same extent as removal of external Na. Its effect was not additive to that of removal of external Na.7. Internal Na ion concentration ([Na(+)](i)), measured using Na(+)-sensitive micro-electrodes, fell on application of (NH(4))(2)SO(4) and increased on its removal. The increase transiently raised [Na(+)](i) above the level recorded before (NH(4))(2)SO(4) application. This overshoot of [Na(+)](i) was almost completely inhibited by amiloride. This is consistent with the involvement of Na(+)-H(+) exchange in the pH(i) regulating system.8. Removal of external CO(2) or application of SITS (10(-4)M) caused some slowing of the rate of pH(i) recovery following acidification by removal of (NH(4))(2)SO(4). The effect of SITS was additive to that of Na-free Ringer or amiloride. These results suggest that Cl(-)-HCO(3) (-) exchange is also involved in the pH(i) regulating system and that it is a separate mechanism. Under the conditions used, Cl(-)-HCO(3) (-) exchange formed about 20% of the pH(i) regulating system.9. Decreasing the temperature from 37 to 28 degrees C not only caused an increase in pH(i), but also considerably slowed the rate of pH(i) recovery following acidification. We have calculated a Q(10) for Na(+)-H(+) exchange of 1.4 and for Cl(-)-HCO(3) (-) exchange, 6.9.10. We conclude that the pH(i) regulating system is comprised of two separate ionic exchange mechanisms. The major mechanism is Na(+)-H(+) exchange, which is probably driven by the transmembrane Na gradient. The other mechanism is Cl(-)-HCO(3) (-) exchange, which probably requires metabolic energy.

Amiloride↗
PubMed1977

The role of bicarbonate, chloride and sodium ions in the regulation of intracellular pH in snail neurones.

1. Intracellular pH (pH(i)), Cl(-) and Na(+) levels were recorded in snail neurones using ion-sensitive micro-electrodes, and the mechanism of the pH(i) recovery from internal acidification investigated.2. Reducing the external HCO(3) (-) concentration greatly inhibited the rate of pH(i) recovery from HCl injection.3. Reducing external Cl(-) did not inhibit pH(i) recovery, but reducing internal Cl(-), by exposing the cell to sulphate Ringer, inhibited pH(i) recovery from CO(2) application.4. During pH(i) recovery from CO(2) application the internal Cl(-) concentration decreased. The measured fall in internal Cl(-) concentration averaged about 25% of the calculated increase in internal HCO(3) (-).5. Removal of external Na inhibited the pH(i) recovery from either CO(2) application or HCl injection.6. During the pH(i) recovery from acidification there was an increase in the internal Na(+) concentration ([Na(+)](i)). The increase was larger than that occurring when the Na pump was inhibited by K-free Ringer.7. The increase in [Na(+)](i) that occurred during pH(i) recovery from an injection of HCl was about half of that produced by a similar injection of NaCl.8. The inhibitory effects of Na-free Ringer and of the anion exchange inhibitor SITS on pH(i) recovery after HCl injection were not additive.9. It is concluded that the pH(i) regulating system involves tightly linked Cl(-)-HCO(3) (-) and Na(+)-H(+) exchange, with Na entry down its concentration gradient probably providing the energy to drive the movement inwards of HCO(3) (-) and the movement outward of Cl(-) and H(+) ions.

Animals↗
PubMed1976

The effects of lithium and sodium on the potassium conductance of snail neurones.

1. The iontophoretic injection of lithium into snail neurones reversibly increased the resting relative potassium permeability (PK). 2. Long exposures to snail Ringer containing 25 mM-Li and correspondingly reduced Na also caused an increase in PK. This did not occur with Ringer in which the same reduction of Na was made by replacing it with Tris. 3. Replacement of part of the Ringer Na by either Li or Tris led to proportional decreases in internal Na. 4. Injecting large quantities of Na into ouabain-treated cells caused effects similar to those of Li injection. Without ouabain, Na injection stimulated the electrogenic Na pump. 5. A number of tests failed to produce any clear evidence that intracellular Ca was involved in the response to Li.

Animals↗
PubMed1976

The effect of carbon dioxide on the intracellular pH and buffering power of snail neurones.

1. Intracellular pH (pHi) was measured using pH-sensitive glass micro-electrodes. The effects on pHi of CO2 applied externally and HCO3-, H+ and NH4+ injected iontophoretically, were investigated. 2. The transport numbers for iontophoretic injection into aqueous micro-droples were found by potentiometric titration to be 0-3 for HCO3- and 0-94 for H+. 3. Exposure to Ringer, pH 7-5, equilibrated with 2-2% CO2 caused a rapid, but only transient, fall in pHi. Within 1 or 2 min pHi began to return exponentially to normal, with a time constant of about 5 min. 4. When external CO2 was removed, pHi rapidly increased, and then slowly returned to normal. The pHi changes with CO2 application or removal gave a calculated intracellular buffer value of about 30 m-equiv H+/pH unit per litre. 5. Injection of HCO3- caused a rise in pHi very similar to that seen on removal of external CO2. 6. The pHi responses to CO2 application, CO2 removal and HCO3- injection were slowed by the carbonic anhydrase inhibitor acetazolamide. 7. H+ injection caused a transient fall in pHi. In CO2 Ringer pHi fell less and recovered faster than in CO2-free Ringer. Calculation of the internal buffer value from the pHi responses to H+ and HCO3- injection gave very similar values. 8. The internal buffer value (measured by H+ injection) was greatly increased by exposure to CO2 Ringer. Acetazolamide reduced this effect of CO2, suggesting that the function of intracellular carbonic anhydrase may be to maximize the internal buffering power in CO2. 9. It was concluded that the internal HCO3- was determined primarily by the CO2 level and pHi, that internal HCO3- made a large contribution to the buffering power, and that after internal acidfication pHi was restored to normal by active transport of H+, OH- or HCO3- across the cell membrane. The active transport was much faster in CO2 than in CO2-free Ringer.

Acetazolamide↗
PubMed1976

Direct measurement of the intracellular pH of mammalian cardiac muscle.

1. The intracellular pH (pHi) of sheep heart Purkinje fibres and rat, ferret and guinea-pig ventricle has been measured using recessed-tip pH-sensitive micro-electrodes. 2. In the absence of CO2 the pHi was approximately 7-2 in all the preparations used. In 5% CO2 the mean pHi was 7-14 in rat and ferret ventricle and 7-02 in sheep Purkinje fibres. 3. The pHi response to an increase or a decrease in the CO2 level (at constant external pH) was biphasic with a large transient change followed by a partial recovery to a new sustained pHi. 4. The intracellular buffering capacity was 34-8 +/- 2-7 m-equiv H+/pH unit per l. (+/- S.E. of mean) in sheep Purkinje fibres, 76-6 +/- 13-6 in rat ventricle and approximately 69 in ferret ventricle. 5. The pHi of all the preparations tested indicated that H+ ions were not passively distributed across the cell membrane. There was also little or no pHi change produced by depolarization with high K solutions. 6. Short exposures to hypertonic solutions (100 mM sucrose or 50 mM-KCl) produced a decrease in pHi of approximately 0-1 pH units. 7. Acetazolamide slowed the pHi response to CO2 changes. 8. Restoration of the pHi after displacement by increasing the CO2 was not blocked by ouabain or SITS. 9. The relationship between pHi and cardiac contractility is discussed.

Acetazolamide↗