Albert Roos

The intracellular pH of frog skeletal muscle: its regulation in isotonic solutions.

The behaviour of intracellular pH (pHi) was studied with micro‐electrodes in frog semitendinosus muscle which was superfused with Ringer solution and with depolarizing solutions. The electrodes were introduced into the depolarized muscle about 40 min after contracture had subsided. All studies were done at external pH (pHo) of 7.35 and at 22 degrees C. The pHi in normal Ringer solution buffered with HEPES was 7.18 +/‐ 0.03 (S.E. of mean) (n = 10); the membrane potential, Vm, was ‐88 +/‐ 1.8 mV. When pHi was lowered to about 6.8 by replacing the HEPES by 5% CO2, 24 mM‐HCO3 (constant pHo), it recovered at a very slow rate of 0.025 +/‐ 0.011 delta pHi h‐1 (n = 6). When all the Na was replaced by N‐methyl‐D‐glucamine (initial pHi 7.20 +/‐ 0.04, initial Vm ‐89 +/‐ 1.5 mV, n = 8), this slow alkalinization was converted into a slow acidification at a rate of 0.069 +/‐ 0.024 delta pHi h‐1. In muscle depolarized in 15 mM‐K (Vm approximately ‐50 mV), the rate of recovery from CO2 acidification was not increased above that in normal Ringer solution (2.5 mM‐K). When, however, the muscle was depolarized in 50 mM‐K to about ‐20 mV, the rate of recovery increased to 0.33 +/‐ 0.07 delta pHi h‐1 (n = 6) when external Cl was kept constant, or to 0.21 +/‐ 0.03 (n = 9) when [K]. [Cl] product was kept constant. In the absence of Na, pHi recovery rate in 50 mM‐K was reduced by at least 90%. Enhanced recovery from CO2‐induced acidification was also observed in 2.5 mM‐K when the fibres were depolarized to about ‐20 mV in one of two ways: (a) by previous exposure for 60 min to 50 mM‐K at constant Cl, or (b) by reduction of external Cl to 5.9 mM in the presence of 0.5 mM‐Ba. When pHi of depolarized fibres (50 mM‐K) was lowered to about 6.8 by the weak acid dimethyl‐2,4‐oxazolidinedione (DMO), it recovered at a rate of 0.12 delta pHi h‐1 in two experiments. In fibres depolarized in 50 mM‐K and constant Cl, either 0.1 mM‐SITS or 0.5 mM‐amiloride slowed pHi recovery from CO2 exposure by about 50%. When the depolarization was achieved at constant [K]. [Cl] product, amiloride slowed pHi recovery by about 50%, while SITS had, at most, only a slight effect.(ABSTRACT TRUNCATED AT 400 WORDS)

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 authors 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.

Effect of calcium and other divalent cations on intracellular pH regulation of frog skeletal muscle.

1. We examined, in frog semitendinosus muscle, the effect of calcium release, induced by depolarization or caffeine, on intracellular pH (pHi) recovery from an acid load applied at least 40 min later. We also studied the effect of external Ca and other divalent cations on recovery. We used pH‐sensitive micro‐electrodes; the external pH (pHo) was always 7.35. 2. In fibres depolarized by 50 mM‐K, constant [K] X [Cl] in the presence of 1 mM‐tetracaine (which blocks Ca release), the rate of pHi recovery from 5% CO2‐induced acidification was 0.15 +/‐ 0.02 delta pHi h‐1 (n = 7), whereas in depolarized fibres that had never been exposed to the drug, the rate of recovery was 0.27 +/‐ 0.01 delta pHi h‐1 (n = 5). Yet, when Ca release was not blocked and the depolarized fibres were exposed to tetracaine shortly before CO2 exposure, a similar slow rate of 0.14 +/‐ 0.03 delta pHi h‐1 (n = 7) was observed. When Ca release was blocked by tetracaine, but the drug washed out before recovery, the rate was again 0.27 +/‐ 0.02 delta pHi h‐1 (n = 6). 3. In fibres first depolarized to about ‐23 mV in 50 mM‐K, constant [K] X [Cl] (recovery of 0.23 +/‐ 0.03 delta pHi h‐1, n = 6), and then repolarized to ‐79 mV in 2.5 mM‐K, the slow rate of recovery was the same (0.03 +/‐ 0.02 delta pHi h‐1) as that in fibres without a history of depolarization and thus of Ca release. 4. In fibres depolarized to ‐50 mV (15 mM‐K, constant Cl) and then exposed to caffeine (4 mM) which releases Ca from intracellular stores, the recovery was the same (0.07 +/‐ 0.03 delta pHi h‐1, n = 5) as in depolarized fibres not exposed to caffeine (0.09 +/‐ 0.01 delta pHi h‐1, n = 5). 5. We conclude that in frog muscle transient Ca release induced by either depolarization or caffeine does not affect the rate of subsequent pHi recovery. Tetracaine reversibly inhibits pHi recovery, but this inhibition is not due to its blocking of Ca release. 6. Recovery from CO2‐induced acidification of fibres depolarized to ‐21 mV in 50 mM‐K, constant Cl was halved, from 0.31 +/‐ 0.04 delta pHi h‐1 (n = 10) to 0.15 +/‐ 0.01 delta pHi h‐1 (n = 13), when external Ca was raised from 4 to 10 mM.(ABSTRACT TRUNCATED AT 400 WORDS)

Acid-base abnormalities in humans associated with the use of the Gibbon-Mayo pump: Flow rates of 2 to 24 liters per square meter of body surface per minute

Summary 1.With use of a Gibbon-Mayo pump with a flow rate of 2 to 2.4 L. per square meter of body surface area per minute and after an average time of 39 minutes of bypass, less metabolic acidosis was found to be present in the blood than was present in the donor blood prior to bypass. The blood oxygen arteriovenous differences are acceptable (artery, 96 per cent; vein, 67 per cent). 2.The poor clinical status, metabolic acidosis, and marked arteriovenous differences in pH, CO 2 , pCO 2 , and oxygen saturation observed in some of the patients develop postoperatively and are probably due to poor cardiac output or vasospasm or a combination of both. Possible causes for this state have been enumerated. 3.Studies are in progress to evaluate directly the cardiac output of these patients in the postoperative state.

Aspects of pH i Regulation in Frog Skeletal Muscle

Publisher Summary Intracellular pH (pH i ) in cells is higher than it would be if H ions were in electrochemical equilibrium. At steady state, this high pH i is maintained by acidifying influences—such as H influx, metabolic acid production, and HCO 3 efflux—suggesting the presence of active transport systems that remove acid equivalents from the cell. This chapter describes the results of studies on pH i regulation in frog skeletal muscle and the changes affecting the steady state pH i . It also describes the properties of the membrane transport systems responsible for pH i regulation and some factors that can modify this regulation. In addition, a comparison between pH i regulation in frog muscle with that in other cells is presented. The membrane transport systems responsible for pH i recovery from acid load in frog muscle fibers are (1) Na–H exchange that can be inhibited by amiloride or by removal of Na from the external medium, and (2) a system that requires HC0 3 , Cl, and Na, can be inhibited by 4-acetamide-4′-isothiocyanatostilbene-2,2′-disulfonic acid (SITS). The Na–H exchanger seems to be equally active in normally polarized and depolarized fibers, whether they are acidified by CO 2 or by an NH 4 Cl prepulse. The SITS-sensitive component manifests itself when the fibers are acidified and depolarized. The resulting elevation of intracellular Cl may be necessary for the appearance of this component of recovery. When normally polarized cells are acidified with CO 2 , an acidifying HCO 3 efflux masks the pH i recovery. The Na–H exchanger in frog muscle is comparable to that in a variety of other vertebrate cells, while the SITS-sensitive component may be more similar to that found in invertebrate nerve and muscle cells.