Calcium Antagonists and Calcium Agonists: Fundamental Criteria and Classification. In: Fleckenstein A, Van Breemen C, Gross R, Hoffmeister F, editors. Cardiovascular Effects of Dihydropyridine-Type Calcium Antagonists and Agonists. Berlin: Springer Berlin Heidelberg; 1985. pp. 3-31. [DOI: 10.1007/978-3-642-70499-4_2]

The role of calcium in blue-light-dependent chloroplast movement in lemna trisulca L

Chloroplast movements are a normal physiological response to changes in light intensity and provide a good model system to analyse the signal transduction pathways following light perception. Blue-light-dependent chloroplast movements were observed in Lemna trisulca using confocal optical sectioning and 3-D reconstruction or photometric measurements of leaf transmission. Chloroplasts moved away from strong blue light (SBL) towards the anticlinal walls (profile position), and towards the periclinal walls (face position) under weak blue light (WBL) over about 20-40 min. Cytoplasmic calcium ([Ca2 + ]cyt) forms part of the signalling system in response to SBL as movements were associated with small increases in [Ca2 + ]cyt and were blocked by antagonists of calcium homeostasis, including EGTA, nifedipine, verapamil, caffeine, thapsigargin, TFP (trifluoperazine), W7 and compound 48/80. Treatments predicted to affect internal Ca2 + stores gave the most rapid and pronounced effects. In addition, artificially increasing [Ca2 + ]cyt in darkness using the Ca2 + ionophore A23187 and high external Ca2 + (or Sr2 + ), triggered partial movement of chloroplasts to profile position analogous to a SBL response. These data are all consistent with [Ca2 + ]cyt acting as a signal in SBL responses; however, the situation is more complex given that both WBL and SBL responses were inhibited to a similar extent by all the Ca2 + -signalling antagonists used. As the direction of chloroplast movement in WBL is exactly opposite to that in SBL, we conclude that, whilst proper regulation of [Ca2 + ]cyt homeostasis is critical for both SBL and WBL responses, additional factors may be required to specify the direction of chloroplast movement.

Influence of diltiazem and/or propranolol on rat blood glucose levels in normal and diabetic animals

Diabetes mellitus and cardiovascular disorders are both common disorders, and it could be anticipated that they coexist in many patients. Diltiazem (DZ) is widely used alone or in combination with propranolol (PROP) for the treatment of hypertension and ischemic heart disease. These drugs could interfere with carbohydrate metabolism and impair glucose tolerance. The purpose of this study was to investigate the effect of oral administration of DZ, PROP (100 and 25 mg kg-1, respectively) and their combination on fasting serum glucose and insulin levels in normal and diabetic Wistar rats. Diabetes was induced by an intraperitoneal (i.p.) injection of streptozotocin (60 mg kg-1). In normal animals, serum glucose was significantly increased after DZ, PROP and DZ/PROP treatment compared to the initial values. In diabetic rats, serum glucose was significantly increased after PROP and DZ/PROP treatments, while it was slightly increased after diltiazem treatment compared to the initial values. In normal animals, plasma cAMP is significantly decreased in all treatment groups compared to the control value, while in the plasma of diabetic rats, cAMP was significantly decreased after PROP and DZ/PROP treatments when compared to the control value. Serum potassium of normal rats decreased after the diltiazem and DZ/PROP treatments, and they tend to increase slightly after PROP treatment. Serum potassium of diabetic rats was increased significantly after PROP and DZ/PROP treatments compared to the initial values. Body weight is decreased significantly in all treatment groups in normal rats while this significant decrease was observed only after DZ/PROP treatment in diabetic rats. This investigation suggests that diltiazem alone has no worsening effects on the glycemic control in diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Dual effect of dihydropyridines on 45Ca uptake induced by the K+ -channel blocker, 4-aminopyridin on mast cells

The 1,4-dihydropyridines (DHP) are calcium antagonists and represent a new class of drugs which act by a selective inhibition of Ca++ influx through voltage-operated calcium channels. We report the effect of nifedipine (Bay A 1040), nisoldipine (Bay K 5552) and nitrendipine (Bay E 5009) on the histamine release and on the 45Ca uptake promoted by 4-aminopyridin in mast cells. These cells treated with DHP (10(-12)-10(-3) M) activated the secretory response in a dose-dependent manner in the range of concentrations 10(-6)-10(-3) M, whereas concentrations of 10(-12)-10(-6) M did not significantly inhibit the secretion. 4-Aminopyridin, a known K+ -channel blocker, induced 45Ca uptake. Pretreatment of mast cells with DHP prior to 4-aminopyridin stimulation inhibited or stimulated 45Ca uptake depending on concentration; thus, concentrations of DHP below 10(-12) of nitrendipine and 10(-9) for nisoldipine and nifedipine were inhibitory, while higher doses potentiated 45Ca uptake. These results demonstrate a diversity of pharmacological effects of DHP on mediator secretion and 45Ca uptake in mast cells and throw into question their only properties as Ca++ antagonists.

Historical overview. The calcium channel of the heart

The present historical paper concentrates on the roots of the pharmacodynamic concept of Ca++ antagonism, and on the various therapeutic consequences of transmembrane Ca++ entry inhibition, i.e., normalization of hyperkinetic cardiac disorders, suppression of arterial and arteriolar spasms, relief of systemic arterial hypertension, stopping of cardiac dysrhythmias. Obviously in all these cases, medicine makes use of the different manifestations of one and the same fundamental action, that is to say, dose-dependent restriction of transmembrane inward Ca++ movements in active myocardium, vascular smooth muscle, or cardiac pacemaker cells. Interestingly, the origin of the principle of Ca++ antagonism and the discovery of drugs that possess Ca++-antagonistic potencies preceded the detection of the "slow Ca++ channels" by some years. However, the subsequent identification of the "slow channels" (or analogous Ca++ transport systems) as the decisive site of action of specific Ca++ antagonists has to be considered a keystone of the actual concept. The present paper does not treat tissue protection by Ca++ antagonists which is provided against intracellular Ca++ overload and its histopathological sequelae, as for instance Ca++-induced myofibrillar or mitochondrial disintegration. However, the inclusion of morphological topics, such as preservation of myocardial and vascular integrity by Ca++ antagonists, would exceed the limits of this article.

Effects of thapsigargin in isolated rat thoracic aorta

The effect of thapsigargin (Tg) was studied in rat thoracic aorta. Tg (10(-8)-10(-5) M) had a dual effect on rat aorta. Thus, Tg induced a concentration dependent increase in basal tone in normal physiological salt solution (PSS), while Tg in potassium (K+) precontracted aortic rings caused a concentration related relaxation and shifted the K+-concentration response curve to the right and depressed the maximal response to K+. Removal of vascular endothelium abolished the relaxant response to Tg and increased the sensitivity of the preparations to the contractile effect of Tg. The contractile response to Tg was resistent to wash-out in drug-free PSS and was not affected by phentolamine, indomethacin or mepyramine but partly reduced by the calcium-antagonist nitrendipine and eliminated by wash-out in calcium-free PSS. Atropine eliminated the endothelium dependent relaxant effect of carbachol, but had no effect on the Tg or on the calcium ionophore A 23187 evoked relaxation. Ultraviolet radiation decreased the relaxant effect of Tg and A 23187 without affecting the carbachol induced relaxations. The results showed that vascular endothelium depressed the contractile effect of Tg and that Tg like A 23187 had an endothelium dependent relaxant effect on rat aorta different from that of carbachol. The results indicate that Tg in vascular smooth muscle acts by stimulating the transmembranal influx of extracellular calcium.

On the relationship between V max of slow responses and Ca-current availability in whole-cell clamped guinea pig heart cells

The relationship between Ca current availability and maximum rate of rise (V max) of slow responses was determined in the same single guinea pig ventricular heart cell under voltage and current clamp conditions (whole-cell clamp technique). The results are as follows. (1) Cell capacitance measured in 32 cells from the current response to a fast ramp voltage-clamp pulse (119.6 +/- 4.6 pF, mean +/- SE) or from Vmax values at a holding potential of -50 or -40 mV (118.6 +/- 5.3 pF) are identical. (2) In control conditions ([Ca]o 1.8, [K]o 4 and [Cs]i 140 mM), voltage-dependence of steady-state inactivation of Ca current (ICa) or Vmax are similar up to -35 mV. However, Vmax significantly (P less than 0.005) underestimates ICa availability at more positive potentials. At -30 mV, ICa and Vmax amplitudes represent respectively 35.6 and 22.4% (n = 14) of their maximum value. (3) In the presence of 50 nM isoprenaline, Vmax and the underlying ICa are respectively increased by 79.2 +/- 13.8% and 71.2 +/- 13.8% (n = 15). No statistically significant deviation from linearity is then observed. (4) When Vmax amplitude is expressed as a function of ICa density, an almost linear relationship is observed for Vmax values between 0 and 25 V/s. Vmax is then best described by the equation: Vmax (V/s) = 1.043 ICa (pA/pF) -0.514 (46 cells). (5) We conclude that, under conditions that minimize outward currents, Vmax of slow responses accurately measures ICa amplitude, except when ICa is decreased to less than 40% of its maximum control amplitude (i.e., below 4 pA/pF). At that point, Vmax underestimates ICa.