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A Roos

Publications and source records attributed to A Roos.

7 recordsLinked to original sources
PubMed1979

pH regulation in barnacle muscle fibers: dependence on intracellular and extracellular pH.

Intracellular pH (pHi) regulation was studied in acid-loaded barnacle muscle fibers by monitoring recovery of pHi with a pH-sensitive microelectrode. By multiplying the rate of pHi recovery by total intracellular buffering power, the acid extrusion rate was obtained. The acid extrusion rate was greatest at low values of pHi, and declined toward zero as pHi approached normal levels. It increased as the extracellular pH (pHo) was raised either by increasing external [HCO3] ([HCO3]o) at constant PCO2 or by decreasing PCO2 at constant [HCO3]o, but more so in the former case than in the latter. These observations suggest that pHo per se is an important determinant of the acid extrusion rate, but that raising [HCO3]o by itself also stimulates acid extrusion. This would be expected if acid extrusion involves the inward movement of HCO3. When fibers were exposed to HCO3-containing solutions at very low or very high pHo, pHi drifted downward or upward, respectively; thbe drifts were inhibited by 4-acetamido-4' isothiocyanostilbene-2,2' disulfonic acid (SITS). Our results are discussed in terms of possible mechanisms of acid extrusion.

Animals↗
PubMed1978

Weak acids, weak bases and intracellular pH.

Against the background of classical observations made 50 years ago, a brief review is offered of some of the work performed in the author's laboratory on the behavior of weak acids and bases towards living animal cells. The significance of membrane permeability of the charged partner of these electrolytes is pointed out, and the existence of an active process of H+ extrusion (or its equivalent) in response to acid loading is demonstrated. The effect of intracellular inhomogeneity on weak acid and base transmembrane distribution is examined. The significance of these variables for weak acid- or base-derived intracellular pH is discussed.

Acid-Base Equilibrium↗
PubMed1978

Intracellular pH transients in rat diaphragm muscle measured with DMO.

Changes of the intracellular pH of rat diaphragm muscle were monitored at 30-min intervals with the weak acid DMO (5,5-dimethyl-2,4-oxazolidinedione). Transferring the muscle from a CO2-containing to a CO2-free solution caused intracellular pH (pHi) to rise by an average of 0.18 during the first 30 min and then to level off at a slightly lower value over the next 60-90 min. Transferring the muscle from a CO2-free to a CO2-containing solution caused pHi to fall by 0.18 during the first 30 min and then to recover by 0.05 over the next 90 min. Subsequent return to the CO2-free solution caused pHi to overshoot the control value by 0.10. Both the recovery and the overshoot can be accounted for by an acid-extruding pump. Intracellular acid loading with 118 mM DMO similarly caused pHi to fall initially, to recover slowly during the acid loading, and then to overshoot the control pHi on removal of the acid load. In the absence of HCO3-/CO2, acid extrusion was reduced by about a fifth. SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid) had no effect. The absence of either Na+ or Cl- from HCO3-/CO2- free solution reduced acid extrusion by about a half.

Animals↗
PubMed1976

Comparison of microelectrode, DMO, and methylamine methods for measuring intracellular pH.

The intracellular pH (pHi) of giant barnacle muscle fibers was measured with glass microelectrodes and also calculated from the distribution of 5,5-dimethyl-2,4-oxazolidinedione (DMO) and methylamine (MA). Simultaneously applying any two of these methods to muscle fibers of the same barnacle, we found the pH measured with an intracellular electrode (pH-Elec) to be about 0.06 higher than the DMO-derived pH (pH-DMO), and pH-DMO to be about 0.10 higher than the MA-derived pH (p-ma). in studies on the pHi of squid giant axons, we found that pH-Elec (7.35) and pH-DMO (7.36) were not significantly different. In the barnacle experiments, DMO required about 30 min to reach a steady-state distribution, while MA required more than 5 h. The deviations of pH-DMO and pH-MA from pH-Elec for the barnacle can be explained by a) an error in the assumed intracellular pKa' of DMO or MA, b) membrane permeability to the ionic form of DMO or MA, or c) intracellular compartmentalization. Included is a detailed study of the apparent dissociation constant of DMO as affected by temperature, and ionic strength and composition.

Animals↗
PubMed1975

Intracellular pH and distribution of weak acids across cell membranes. A study of D- and L-lactate and of DMO in rat diaphragm.

1. The steady-state distribution ratios of D- and L-lactate between fibre water and external fluid were measured in 'intact' rat hemidiaphragm preparations exposed for 2-5 hr to a variety of solutions of normal ionic strength and osmolarity. The studies were designed to minimize the effects, on these distributions, of conversion of lactate and of generation of lactic acid by the muscle. 2. At D-lactate concentrations between 2.3 and 118 mM, at normal pH and PCO2, the D-lactate distribution ratio, obtained from the distribution of [2-(3)H]D-lactate was independent of concentration; it averaged 0.349. As the concentration of D-lactate was reduced below 2.3 mM, its distribution ratio progressively fell to less than 0.1. 3. Radiochromatograms of extracts of incubated muscle showed that the tritium label was not attached to substances other than lactate. 4. At L-lactate concentrations of 59 and 108 mM, at normal pH and PCO2, the average L-lactate distribution ratios, obtained by enzymatic analysis, were respectively 0.395 and 0392. 5. At 19-89 mM D-lactate, depolarizing the muscle fibres by high K(49-127 mM), at normal pH, PCO2, and [K]0[Cl]0 product, only slightly affected the D-lactate distribution ratio which averaged 0.405. 6. The D-lactate distribution ratio and intracellular pH (pHi), obtained with the DMO method (5,5-dimethyl-2,4-oxazolidinedione), were measured in thirty sets of studies after exposure of the muscle to solutions buffered to pH values ranging between 5.99 and 8.13, and containing 18.5-118 mM D-lactate and 6-129 mM-K. 7. The relation between the distribution ratios of D-lactate ([TL]i/[TL]O) and of H ions ([Ho/[H]i) in these studies could be expressed by [TL]i/[T]O = 0.646 [H]o/[H]i+0.056. 8. It was concluded that it is predominantly the undissociated lactic acid molecules, rather than the much more numerous lactate ions, which permeate the fibre membrane; and that the steady-state lactate distribution ratio is determined by the transmembrane pH gradient, and not by membrane potential. 9. The expression of the steady-state lactate distribution ratio as function of relative membrane permeabilities of lactic acid molecule and lactate ion, membrane voltage, and internal and external H ion concentrations indicates that a finite permeability to the ion, three or four orders of magnitude less than that to the molecule, is compatible with the experimental data. When both ion and molecule of any weak acid are permeable, they act as a carrier system for the movement of protons down their electrochemical gradient. 10. Near-maintenance of pHi in the face of high fibre D-lactate (19-44 mM) and DMO (8-42 mM) indicates stimulation of proton extrusion by acid loans. 11. This extrusion is insensitive to ouabain, as judged from the lack of effect of the drug of pHi with acid loading.

Animals↗