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Biomedical subjects

E Rumberger

Publications and source records attributed to E Rumberger.

At least 37 records · Page 2Linked to original sources
PubMed1986

[Electrophysiologic and intropic effects of dantrolene on isolated ventricular myocardium. Studies on guinea pig papillary muscle].

The effect of dantrolene (D) on transmembrane potential and contractile force was examined in electrically driven right ventricular papillary muscles of guinea-pigs. Independent of stimulation frequency D (100 mumol/l) caused a significant reduction of contractility by ca. 40% from control levels. Action potential duration measured at the 90% and 50% repolarisation level was significantly increased while plateau phase was slightly depressed by D. Resting membrane potential, action potential amplitude and maximum rate of depolarisation in phase 0 were unaffected. The effect of D on action potential duration was significantly dependent upon the frequency of stimulation. At faster rates action potential duration was increased relatively more than at slower rates. Slow response action potentials were unaffected by D. Unlike Ryanodine D did not flatten the force-frequency-relationship curve and did not influence the force-interval-relationship under extrastimulation. - It is concluded that the direct negative inotropic effect of D is not accompanied by a transsarcolemmal influence such as an inhibition of fast Na+- or slow Ca++-channels. The results are compatible with an intracellular site of action of D as postulated for skeletal muscle. D acts differently from ryanodine, another presumed inhibitor of sarcoplasmic reticulum.

Action Potentials↗
PubMed1976

Age-changes of the force-frequency-relationship and the duration of action potential of isolated papillary muscles of guinea pig.

The force-frequency-relationship and the duration of the action potential recorded intracellularly were compared on isolated isometrically arranged papillary muscles of young (3--4 months old) and senile (36--40 months old) guinea pigs. The muscles were in Krebs-Henseleit-solution at 37 degrees C electrically stimulated with frequencies between 30 and 420 imp./min. The following results were obtained: 1. The isolated papillary muscles of the two groups are almost similar with respect to length, weight and cross-sectional are. 2. In the range of stimulation rate from 30--420 imp./min the duration of action potential in the senile group was 120--135% of that in the young group. 3. The shape of slow repolarization of action potential was steeper in the senile group. 4. The time to peak tension and the relaxation time were longer in the senile group. 5. The maximally developed tension was the same in both groups, but in the senile group it was reached at a stimulation rate of 120 imp./min whereas in the young group, the optimal frequency was 290 imp./min. 6. The greatest value for the maximal rate of tension rise was 2.4 times smaller in the senile group. The results are discussed in relation to the age dependent intensity of membrane currents and to a possible altered activity of sarcoplasmic reticulum.

Action Potentials↗
PubMed1976

The role of the sarcoplasmic reticulum in the pure frequency potentiation: the effect of ryanodine.

The dependence of the contraction amplitude of the isolated papillary muscle of the guinea pig on the stimulation pattern is probably caused by a well working sarcoplasmic reticulum. This view is supported by the finding that the alkaloid ryanodine flattens the curve of the force-frequency relationship and abolishes the pure frequency potentiation. Ryanodine is said to destroy exclusively the connection between T-tubulus and sarcoplasmic reticulum.

Alkaloids↗
PubMed1976

[The effect of sudden changes in the stimulation rate of the heart on peak systolic pressure (author's transl)].

The changes in systolic pressure were studied in 48 patients during artificially (by electrical stimulation) induced sudden increases and consecutive decreases in heart rate. Various patterns could be separated respective to phase A (sudden switch from low (80-120 impulses/min) to higher heart rate (140-180 impulses/min)) and to phase B (sudden switch-back from high to lower (control) beating rate): AI) The systolic peak-pressure of the first contraction after the shortened stimulation interval is very low and often stays ineffective (below the aortic opening pressure). The second contraction develops already a higher pressure than the first one, during the consecutive beats the systolic pressure increases gradually until a new steady state is reached, which is usually lower than the systolic pressure during the foregoing lower beating rate. Sometimes however it can be equal or even higher. Accordingly after an elevation of heart rate arterial mean pressure can drop, stay constant or increase. AII) The systolic peak-pressure of the first contraction after the shortened stimulation interval stays relatively high and drops continuously with the succeeding contractions until a new steady state is reached according to the higher heart rate, it is however always lower than the one at a lower stimulation rate. Therefore arterial mean pressure is always decreased. AIII) Finally we observed changes in arterial systolic pressure in some patients that could not be grouped according to one or to the other pattern described above.- BI) The systolic peak of the first contraction after the switch-back from the high to the lower (control) rate is much higher than that of the last at the higher rate. The peak pressures of the consecutive contractions are then dropping continuously to the new steady-state, that can be higher, equal or lower than that at the higher stimulation rate. BII) ....

Adolescent↗