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D Rampe

Publications and source records attributed to D Rampe.

45 records · Page 3Linked to original sources
PubMed1988

Control of expression of the 1,4-dihydropyridine receptor in BC3H1 cells.

To determine whether expression of the 1,4-dihydropyridine receptor of skeletal muscle Ca2+ channels is regulated by signals that impinge on muscle-specific gene expression, BC3H1 muscle cells were analyzed using (+)[3H]PN200-110 as a probe for the receptor. No dihydropyridine binding sites were detected in proliferating cells. Binding site density increased following serum withdrawal, peaking at day six, with little or no change in Kd (approximately equal to 250 pM, similar to that seen in skeletal muscle). No DHP binding sites were detected in BC3H1 cells bearing an activated c-H-ras oncogene. Induction of the dihydropyridine receptor was reversibly blocked by 200 pM transforming growth factor beta. The results indicate that formation of dihydropyridine-sensitive Ca2+ channels may require up-regulation of the dihydropyridine receptor itself, and that transforming growth factor beta is a potent, reversible inhibitor of this receptor in BC3H1 muscle cells.

Animals↗
PubMed1987

Benzodiazepine interactions at neuronal and smooth muscle Ca2+ channels.

Ro 5-4864 and PK 11195, ligands for the peripheral benzodiazepine binding site, blocked 45Ca2+ uptake into depolarized guinea-pig cortical synaptosomes. The fast phase of uptake was significantly more sensitive than the slow phase. The central benzodiazepine ligands, Ro 15-1788 and beta-CCE at 10(-4) and 5 X 10(-5) M respectively, were less effective and did not discriminate between fast and slow uptake phases. Ro 5-4864 and PK 11195 inhibited and potentiated respectively the binding of [3H]nitrendipine to synaptosomes by effects on the KD value. PK 11195 (10(-5) M), blocked K+ depolarization and Bay K 8644-induced tension responses in guinea-pig ileal longitudinal smooth muscle. Benzodiazepines do interact with voltage-dependent Ca2+ channels but the present data are insufficient to prove direct coupling of peripheral benzodiazepine sites with Ca2+ channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

The actions of diazepam and diphenylhydantoin on fast and slow Ca2+ uptake processes in guinea pig cerebral cortex synaptosomes.

The activities of diazepam and diphenylhydantoin as inhibitors of the fast and slow phases of 45Ca2+ uptake in response to K+ depolarization and of [3H]nitrendipine binding were examined in guinea pig cerebral cortex synaptosomes. The slow phase of 45Ca2+ uptake was abolished in Na+-free media (choline substitution) and was more sensitive to inhibition by 3,4-dichlorobenzamil and represents a Na+-dependent Ca2+ uptake process. The fast component of uptake represents activation of voltage-dependent Ca2+ channels. Diazepam (to 300 microM) was selectively active against the fast component of 45Ca2+ uptake. The benzodiazepines Ro 11-3624 and Ro 11-3128 were similarly selective with a modest stereoselectivity against the fast component of 45Ca2+ uptake. Diphenylhydantoin (100 and 200 microM) blocked nonselectively both fast and slow phases of Ca2+ uptake. Diazepam (60 microM) and diphenylhydantoin (200 microM) blocked [3H]nitrendipine binding in a competitive manner. Diazepam and diphenylhydantoin probably exert at least part of their anticonvulsant activity by inhibition of voltage-dependent Ca2+ channels.

Animals↗
PubMed1987

Comparative aspects and temperature dependence of [3H]1,4-dihydropyridine Ca2+ channel antagonist and activator binding to neuronal and muscle membranes.

Binding of [3H]nitrendipine, [3H]nimodipine, and (+)[3H]PN 200-110 to microsomal preparations of guinea pig smooth and cardiac muscle and brain synaptosomes revealed high affinity interaction with KD values in the sequence, (+)PN 200-110 greater than nitrendipine greater than nimodipine. Bmax values for a particular tissue were independent of the 1,4-dihydropyridine employed in radioligand binding at 25 degrees C. The temperature dependence of [3H]nitrendipine binding in cardiac and smooth muscle microsomal preparations and brain synaptosomes was measured from 0 degrees to 37 degrees C and for skeletal muscle preparations from 0 degrees to 30 degrees C. Bmax values increased with temperature for cardiac membranes, but did not vary in other tissues. van't Hoff plots were nonlinear in all tissues, enthalpy and entropy changes becoming increasingly negative with increasing temperature. Competition binding of the activator-antagonist enantiomeric 1,4-dihydropyridine pairs of Bay k 8644 and PN 202-791 for [3H]nitrendipine in smooth muscle did not reveal significant thermodynamic differences between activator and antagonist molecules.

Animals↗
PubMed1987

Electrophysiologic and biochemical studies on the putative Ca++ channel blocker MDL 12,330A in an endocrine cell.

MDL 12,330A is a molecule structurally unrelated to other organic Ca++ channel ligands that may alter Ca++ channel function. Using whole cell patch clamp, [3H]PN200-110 binding and 45Ca++ uptake studies, we examined the effects of this compound on voltage-dependent Ca++ channels in rat anterior pituitary cells. At a concentration of 10(-5) M, MDL 12,330A showed little effect on outward K+ current, Na+ current or low-threshold Ca++ current in this cell line. At 10(-6) M, MDL 12,330A reversibly inhibited slow Ca++ current in a voltage-dependent manner. 45Ca++ uptake was also blocked by this compound at 10(-6) M, whereas [3H]PN200-110 binding was stimulated at concentrations of 10(-7) to 10(-6) M. The results are consistent with an interaction of MDL 12,330A with slow Ca++ channels at a site allosterically linked to the 1,4-dihydropyridine binding site.

Animals↗
PubMed1986

The ontogeny of [3H]nitrendipine binding sites and 45Ca2+ uptake processes in brain synaptosomes from spontaneously hypertensive rats.

Potassium-stimulated 45Ca2+ uptake into rat brain cerebral cortex synaptosomes was measured in spontaneously hypertensive rats at ages two days to 140 days. The fast and slow phases of 45Ca2+ uptake were measured. The slow phase was abolished by replacement of Na+ by choline, was more sensitive to 3,4-dichlorobenzamil and likely represents Na+:Ca2+ exchange. The fast and slow phases of 45Ca2+ uptake developed at different rates, the slow phase developing more rapidly and being more prominent at younger ages, but both phases were at a maximum at 5 weeks. [3H]Nitrendipine binding increased from 2 days (Bmax = 39 +/- 1 fmol mg-1 protein), without change in Kd (mean = 130 +/- 7 X 10(-12) M). Development of [3H]nitrendipine binding paralleled that of the fast phase of 45Ca2+ uptake. Neither 45Ca2+ uptake (both phases) nor [3H]nitrendipine binding (Bmax) changed between 5 weeks (prehypertensive) and 20 weeks (established hypertensive) of age.

Age Factors↗
PubMed1984

Specific binding of a calcium channel activator, [3H]BAY k 8644, to membranes from cardiac muscle and brain.

BAY k 8644 is a member of a new class of drugs that directly activates Ca2+ channels. This 1,4-dihydropyridine was found to bind to both high and low affinity sites on rabbit ventricular microsomes and guinea pig brain synaptosomes. The dissociation constant obtained from Scatchard analysis with [3H]BAY k 8644 was 2 to 3 nM for the high affinity binding site, and the estimated maximal number of binding sites was 0.8 and 0.4 pmol/mg protein for heart and brain membranes, respectively, at 15 degrees C. Competition between nitrendipine and [3H]BAY k 8644 indicated a common high affinity binding site for Ca2+ channel activators and antagonists. The results suggest that the 1,4-dihydropyridine Ca2+ channel antagonists do not act as simple channel plugs.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1984

BAY K 8644, a 1,4-dihydropyridine Ca2+ channel activator: dissociation of binding and functional effects in brain synaptosomes.

K+-stimulated 45Ca2+ uptake into rat brain and guinea pig cerebral cortex synaptosomes was measured at 10 s and 90 s at K+ concentrations of 5-75 mM. Net increases in 45Ca2+ uptake were observed in rat and guinea pig brain synaptosomes. 45Ca2+ uptake under resting or depolarizing conditions was not increased by the 1,4-dihydropyridine BAY K 8644, which has been shown to activate Ca2+ channels in smooth and cardiac muscle. High-affinity [3H]nitrendipine binding in guinea pig synaptosomes (KD = 1.2 X 10(-10) M, Bmax = 0.56 pmol mg-1 protein) was competitively displaced with high affinity (IC50 2.3 X 10(-9) M) by BAY K 8644. Thus high-affinity Ca2+ channel antagonist and activator binding sites exist in synaptosome preparations, but their relationship to functional Ca2+ channels is not clear.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗