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Biomedical subjects

H G Haas

Publications and source records attributed to H G Haas.

At least 73 records · Page 4Linked to original sources
PubMed1976

Calcium-sodium antagonism on the frog's heart: a voltage-clamp study.

1. In double sucrose-gap voltage-clamped frog atrial fibres the influence of [Ca]o and [Na]o on membrane current and contraction was investigated. 2. The slow (secondary) inward current varied with [Ca]o but was almost insensitive to changes in [Na]o. In contrast, the phasic (transient) contraction initiated by the slow inward current was affected by both [Ca]o and [Na]o. 3. With moderate changes of [Ca]o and [Na]o from normal, the strength of phasic contraction at a given depolarization followed the [Ca]o/[Na]2o ratio approximately. This was best seen at membrane potentials near zero level. 4. Under the same conditions, tonic (sustained) contractions associated with prolonged depolarizations were strictly correlated to the [Ca]o/[Na]2o ratio at any potential. No interrelation between tonic tension and steady-state current was found. 5. With extensive changes in [Ca]o and [Na]o, the sensitivity of both phasic and tonic tension to the [Ca]o/[Na]2o ratio declined, the negative effect of [Na]o becoming smaller than was expected from this ratio. 6. In Na-free choline-Ringer, a strong contracture developed followed by a spontaneous relaxation. Starting from the relaxed state, application of depolarizing clamps gave rise to phasic contractions with a very slow relaxation while tonic contractions were apparently lacking. 7. The results are interpreted in terms of an energy-dependent carrier mechanism exchanging one Ca for two Na ions across the cell membrane. The model implies a strong asymmetry in the rate constants governing the chemical reactions on both sides of the membrane. The system is thought to operate close to equilibrium at any potential, thereby determining the steady level of myoplasmic Ca. The equilibrium itself is considered to shift upon depolarization. Assuming that [Na]i is constant, the steady level of [Ca]i is expected to be proportional to the [Ca]o/[Na]2o ratio, the scale factor being a function of membrane potential. 8. The carrier model suggests the occurrence of a depolarization-induced inward transfer of Ca which might be involved in the generation of tonic contractions. 9. The apparent lack of tonic contractions in the absence of external Na ions may be explained by a suppression of carrier-mediated Ca influx normally occurring upon depolarization. 10. The antagonistic effects of [Ca]o and [Na]o on phasic contraction are understood as being due to alterations of the Ca pumping system rather than changes in slow inward current.

Action Potentials↗
PubMed1975

[Hypo and hypercalcemia as an emergency].

1. Hypo- and hypercalcemia can be explained as derangements of the calcium homeostasis. Hypocalcemic tetany usually alarming the patient tremendously is, at least in adults, rarely life-threatening. Hypercalcemia leads in 30% of the cases to clinical symptoms which may inadvertedly pass into a state of hypercalcemic crisis. This latter requires an often difficult emergency treatment. 2. Hypocalcemic tetany may be reversed by administering calcium i.v. or, in severe cases, by a calcium infusion. Only rarely are magnesium supplements necessary to let the tetany disappear. Vitamin D or dihydrotachysterol (DHT) do not correct hypocalcemia immediately, since their effects may be delayed up to 15-25 days. In order to normalize the serum calcium permanently, vitamin D or DHT treatment should be instituted as rarely as possible. 3. Initially, hypercalcemic crisis is best treated by forced intravenous fluid administration with normal saline (and furosemide) in combination with high doses of prednisone. Fluid-, sodium- and potassium balances ought to be checked during this type of treatment. A first evaluation of the effectiveness of these measures is recommended after 24 hours: treatment is continued in patients who respond favorably, while subjects who do not show a significant decrease of the serum calcium may either be given a phosphate infusion or mithramycine as a bolus. Calcitonin appears to be useful only to start treatment before institution of a phosphate infusion.

Calcium↗
PubMed1975

The metabolic balance technique: a critical reappraisal.

Twenty-six metabolic balance studies (MBS) of Ca, Mg, and P have been conducted in 11 postmenopausal women with osteoporosis and in 4 patients suffering from Paget's disease of bone. Subjects were given a liquid formula diet (LFD) matched as closely as possible to the patient's home diet. Studies lasted for 25 days, separated into 5-day periods by a carmine marker combines with Cr2O3 as continuous fecal marker. The balance studies were combined with a tracer technique using 47Ca to detect a possible loss of Ca by perspiration. The reliability of analytical methods necessary for mineral balances was tested. In 22 of the 26 MBS a steady state (SS) reflecting the patient's regular living conditions was demonstrated, while a non-SS situation possibly due to changes of physical activity was seen in four instances. The overall precision and accuracy of this balance method for Ca and P was found to be better than plus or minus 50 mg/day after four periods and plus or minus 40 mg/day after five periods, as related to an average daily intake of 920 mg Ca and 1230 mg P. For Mg (intake 190 mg/day), a precision of plus or minus 10 mg/day was recorded. The dermal loss of Ca was found to be less than 20 mg/day. As shown for Ca, Mg and P, the precision of a balance study is only little enhanced when the investigation is continued for more than four periods. At the present time is not possible to predict non-SS situations before starting such a study but a simple formula is proposed to detect those which were not performed under SS conditions.

Calcium↗
PubMed1975

Effects of prenylamine on cardiac membrane currents and contractility.

The influence of prenylamine on the electrical and mechanical activity of frog atrial muscle fibers has been studied under voltage clamp conditions. At a concentration of 10-4 M, prenylamine blocks the action potential without much affecting the resting potential. The drug depresses the peak transient sodium conductance with a dissociation constant of 1.7 times 10-5 M and on a one-to-one stoichiometric basis. The curve relating peak sodium conductance to membrane potential is slightly shifted in the direction of hyperpolarization. The time to peak sodium current and the rate of sodium inactivation are not significantly altered. With 2 times 10-5 M prenylamine, the steady-state sodium inactivation curve is shifted by 5 mV to more negative membrane potentials but the decreased availability of the sodium system at the resting level is not sufficient to account for the reduction of sodium current. Recovery from sodium inactivation upon repolarization is distinctly slowed. The slow (secondary) inward current carried by calcium and/or sodium and the steady-state outward current are also depressed by prenylamine. The phasic (twitch-like) contraction related to the slow inward current is slightly decreased. The tonic (sustained) contraction associated with long-lasting depolarizations is increased and the time course of relaxation is retarded by prenylamine.

Action Potentials↗
PubMed1975

[Food analysis for balance studies, especially calcium, magnesium, phosphorus and nitrogen].

The calcium-, magnesium-, phosphorus-, nitrogen- and water-contents have been estimated in raw and processed foods (bread and sausages). These results were then compared with the data in food tables. Surprisingly small differences were recorded, since content-deviations of processed foods are equalized in a whole day menu. Thus, food tables proved to be reliable for the calculation of balance and test diets.

Calcium↗