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Perpetuation of misinterpretations due to lack of methodical insight. A critical re-evaluation of the determination of 45Ca release from intact guinea-pig atria

100%

Hein L., Lullmann H., Schoch R.

Journal of Physiology and Pharmacology

1991

tom 42

nr 1

1. The evaluation of still more pretentious and complicated methods is accompanied by a decline of methodical knowledge outside of the own technical field. Interpretations or extrapolations are taken as granted without critical examination of the methodical steps applied. An example is given by re-evaluating the ⁴⁵Ca release from isolated cardiac tissue and the possible interpretations. 2. ⁴⁵Ca release and tissue Ca content were measured in isolated guinea-pig left atria during Ca equilibrium and under conditions known to induce net Ca movements. 3. At equilibrium condition (1.8 mM Na²⁺ ₀)3 exponential phase of ⁴⁵Ca release from the atria were observed. The compartments contained 61%, 29% and 10% of total ⁴⁵Ca; the were 2, 12 and 90 min, respectively. 4. The release of ⁴⁵Ca from the slowly exchanging compartment (t½ 90 min) decreased during incubation in nominal Ca-free solution, although a net loss of tissue Ca occurred. Addition of EGTA (5 x 10⁻⁵ M) to the washout medium abolished this retardation of ⁴⁵Ca release. 5. At external Na⁺ concentrations below 40 mM (substituted by sucrose), the ⁴⁵Ca release from the slowly exchanging compartment decreased. Simultaneously, the tissue Ca content increased massively. The ⁴⁵Ca release was further reduced in Na-poor, nominal Ca-free solution. Under both conditions, the presence of EGTA in the washout medium normalized the rate of ⁴⁵Ca release. 6. The results suggest that the apparent decline of ⁴⁵Ca release from intact atria upon reduction of the external Ca and Na concentration does not reflect a decrease of the cellular efflux rate, but is the consequence of an enhanced re-uptake of ⁴⁵Ca from the extracellular space into the myocardial cells. The probability for the released ⁴⁵Ca either to escape into the organ bath or to become reabsorbed depends on the specific radioactivity of ⁴⁵Ca in the extracellular space during the washout phase. Thus, this experimental procedure is not suited to demonstrate a Na-Ca exchange at the cardiac sarcolemma.

Fluidising effect of resorcylidene aminoguanidine on sarcolemmal membranes in streptozotocin-diabetic rats: blunted adaptation of diabetic myocardium to Ca2plus overload

84%

Waczulikova I., Ziegelhoffer A., Orszaghova Z., Carsky J.

Journal of Physiology and Pharmacology

2002

tom 53

nr 4,2

The "remodelling" of cardiac sarcolemma in diabetes is believed to underlie the reduced sensitivity of diabetic hearts due to their overload with extracellular calcium. Along with a non-enzymatic glycosylation and the free radical-derived glycoxidation of sarcolemmal proteins there is ongoing reduction in cardiomyocyte membrane fluidity, the modulator of cardiac sarcolemmal functioning. Aminoguanidine derivatives, that inhibit glycation and glycoxidation, might suppress myocardium "remodelling" occurring in diabetic heart. To verify this hypothesis, we studied physical parameters of cardiac sarcolemma from the streptozotocin-induced diabetic rats (45 mg.kg-1 i.m.) treated with resorcylidene aminoguanidine (RAG, 4 or 8 mg.kg-1 i.m.). The treatment with RAG not only completely abolished protein glycation and a generation of free oxygen species (p<0.001) in treated diabetic animals, but also considerably attenuated the decrease in sarcolemmal membrane fluidity (p<0.001). In diabetic animals the "normalizatio". of the sarcolemmal membrane fluidity was accompanied by the vastly increased susceptibility of diabetic hearts to be overload with external calcium. We concluded that the decreased fluidity of the sarcolemmal membrane, apparently linked to the excessive glycation of sarcolemmal membrane proteins, might be intimately connected with the adaptation mechanism(s) that are likely to develop in diabetic heart to protect it against the overload with external calcium.

The influence of Nifedipine and Verapamil on the ischaemia-induced changes in canine sarcolemmal membranes

84%

Kobusiewicz W., Ogonowska-Kobusiewicz M., Michalak J., Ledwozyw A.

Archivum Veterinarium Polonicum

1995

tom 35

nr 1-2

Ograniczanie wyników

2 Journal of Physiology and Pharmacology

1 Archivum Veterinarium Polonicum

1 Carsky J.

1 Hein L.

1 Kobusiewicz W.

1 Ledwozyw A.

1 Lullmann H.

1 Michalak J.

1 Ogonowska-Kobusiewicz M.

1 Orszaghova Z.

1 Schoch R.

1 Waczulikova I.

1 Ziegelhoffer A.

1 2002

1 1995

1 1991

Wyniki wyszukiwania

Perpetuation of misinterpretations due to lack of methodical insight. A critical re-evaluation of the determination of 45Ca release from intact guinea-pig atria

Fluidising effect of resorcylidene aminoguanidine on sarcolemmal membranes in streptozotocin-diabetic rats: blunted adaptation of diabetic myocardium to Ca2plus overload

The influence of Nifedipine and Verapamil on the ischaemia-induced changes in canine sarcolemmal membranes