Calcitonin gene-related peptide as modulator of cholecystokinin-induced contraction of guinea pig gall bladder strips in vitro.
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Animals↗
Biomedical subjects
P K Pang
Publications and source records attributed to P K Pang.
GTP gamma S activates calcium channels in neonatal rat ventricular cells.
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Action Potentials↗
Modification by solvents of the action of nifedipine on calcium channel currents in neuroblastoma cells.
The effect of nifedipine dissolved in different solvents on the two types of calcium channel currents in neuroblastoma cells was investigated using the whole cell version of the patch clamp technique. Nifedipine dissolved in dimethylsulfoxide (nifedipine/DMSO) decreased the transient calcium channel (T channel) current by 50% at a concentration of 10 microM. This inhibitory effect was concentration-dependent and reversible. In contrast, T channel currents were not inhibited by nifedipine at a similar concentration dissolved in acetone or ethanol. Further experiments were carried out with dried nifedipine/DMSO. Dried nifedipine/DMSO powder re-dissolved in acetone or ethanol at a concentration of 10 microM decreased the T channel current by 32% and 37%, respectively. In addition, within the concentration range of 10 nM to 100 microM nifedipine/DMSO inhibited the long-lasting calcium channel (L channel) current more effectively than did nifedipine dissolved in acetone. The concentration of solvent (DMSO, ethanol, acetone) in the bath was fixed at 0.3% to reach different final concentrations of nifedipine. Solvents alone at a final concentration of 0.3% did not show any effect on T or L channel currents. UV absorbance measurements indicated that the combination of nifedipine, solvent and bath solution did not result in precipitation of the dihydropyridine during the experimental protocol. It is concluded that when DMSO is used as the solvent, nifedipine is not only a more effective L channel antagonist but also a T channel antagonist in neuroblastoma cells.
Acetone↗
Actions of cadmium on basolateral plasma membrane proteins involved in calcium uptake by fish intestine.
The inhibition of Ca(2+)-ATPase, (Na+ + K+)-ATPase and Na+/Ca2+ exchange by Cd2+ was studied in fish intestinal basolateral plasma membrane preparations. ATP driven 45Ca2+ uptake into inside-out membrane vesicles displayed a Km for Ca2+ of 88 +/- 17 nM, and was extremely sensitive to Cd2+ with an IC50 of 8.2 +/- 3.0 pM Cd2+, indicating an inhibition via the Ca2+ site. (Na+ + K+)-ATPase activity was half-maximally inhibited by micromolar amounts of Cd2+, displaying an IC50 of 2.6 +/- 0.6 microM Cd2+. Cd2+ ions apparently compete for the Mg2+ site of the (Na+ + K+)-ATPase. The Na+/Ca2+ exchanger was inhibited by Cd2+ with an IC50 of 73 +/- 11 nM. Cd2+ is a competitive inhibitor of the exchanger via an interaction with the Ca2+ site (Ki = 11 nM). Bepridil, a Na+ site specific inhibitor of Na+/Ca2+ exchange, induced an additional inhibition, but did not change the Ki of Cd2+. Also, Cd2+ is exchanged against Ca2+, albeit to a lesser extent than Ca2+. The exchanger is only partly blocked by the binding of Cd2+. In vivo cadmium that has entered the enterocyte may be shuttled across the basolateral plasma membrane by the Na+/Ca2+ exchanger. We conclude that intracellular Cd2+ ions will inhibit plasma membrane proteins predominantly via a specific interaction with divalent metal ion sites.
Animals↗
Structure-cardiovascular activity relationships of parathyroid hormone.
The effects of parathyroid hormone (PTH) analogues on isolated rat tail arteries and frog arteries and heart were examined. Synthetic bovine PTH fragment 1 to 34 [bPTH-(1-34)], porcine PTH-(1-34), [Ala1] pPTH-(1-34), and [Nle8] pPTH-(1-34) were tested for vasorelaxant activity on helical strips of the rat tail artery and the frog iliac and femoral artery, preconstricted with arginine vasopressin or arginine vasotocin in the rat and the frog, respectively. For cardiac activity, PTH analogues were administered to isolated frog atria, and atrial rate and atrial tension (AT) were measured. The N-terminal amino acid alanine appears to be pivotal for vasorelaxant activity of PTH molecules on the rat tail artery strips. Data from the frog preparations supported the finding in the rat, although the iliac and femoral arterial preparations differed in their responses. The N-terminal serine in pPTH-(1-34), compared with the other PTH analogues, appeared to be responsible for different cardiac responses, being negatively chronotropic and without effect on AT.
Animals↗
Calcitonin gene-related peptide: an inhibitor of bullfrog (Rana catesbeiana) gallbladder contraction in vitro.
The presence of a calcitonin gene-related peptide (CGRP)-like material was demonstrated in the gallbladder of the bullfrog, Rana catesbeiana, using immunocytochemistry and confirmed by radioimmunoassay. An intense immunocytochemical reaction was observed in nerves located in the smooth muscle layers and associated with blood vessels. No immunoreactive nerve fibers were associated with ganglia, nor were immunoreactive cell bodies observed. Radioimmunoassay showed that 25.03 +/- 2.5 pmol/g tissue of CGRP-like material was present. In vitro tension studies using gallbladder strips showed that CGRP exerted an inhibitory effect on both acetylcholine- and cholecystokinin octapeptide-induced tension but had no effect on KCl-, norepinephrine-, or cerulein-induced tension. CGRP may act directly on the gallbladder smooth muscle to inhibit contraction.
Acetylcholine↗
Mitogenic and tumor necrosis factor producing activities of Pseudostellaria heterophylla.
Separation of mitogenic fraction (PH-I) from Pseudostellaria heterophylla and characterization of its biological activities were investigated. PH-I was isolated as an alcohol-insoluble fraction from the hot water extract obtained by heating the roots of P. heterophylla in water at 80 degrees C for 4 h. It is a water-soluble substance consisting of mainly carbohydrates (56.8%) and a small amount of proteins (7.6%). The incorporation of tritiated thymidine into the DNA of murine spleen lymphocytes could be stimulated by PH-I in a dose-dependent manner. PH-I could act as a priming agent for the release of tumor necrosis factor (TNF) in mice. Moreover, PH-I exhibited potent anti-tumor activities against Ehrlich ascites tumor (EAT) cells in vivo but not in vitro.
Animals↗
Cardiac activity of calcitonin gene-related peptide in amphibian species (Rana tigrina, Triturus sp).
1. Calcitonin gene-related peptide (CGRP) produced dose-related positive chronotropic and inotropic responses in isolated atria of a newt, Triturus sp. and a frog, Rana tigrina. It was apparent that CGRP was stimulatory on the heart of the amphibian species. 2. In the frog, these dose-related responses were attenuated in the presence of a CGRP antagonist (hCGRP 3 x 10(-8) M). This was indicative of the presence of cardiac CGRP receptors. 3. In the presence of beta-adrenergic (propranolol 10(-6) M) and calcium channel (verapamil 10(-8) M, but not nifedipine 10(-8) M) blocker, the basal AR in the frog were decreased. AR induced by CGRP were increased however. 4. The maximal AR and AT responses of the isolated atria to CGRP were not affected by the presence of propranolol. 5. In the presence of calcium channel blockers (verapamil and nifedipine), the maximal AT response was attenuated. These changes suggest the cardiac effects of CGRP are related to calcium mobilization.
Animals↗
Responsiveness to synthetic parathyroid hormone in the portal vein of portal hypertensive rats.
In addition to its hypotensive action, the parathyroid hormone also decreases portal pressure in portal hypertensive rats. The purpose of this study was to characterize the vascular effects of the parathyroid hormone on the portal vein of portal vein-stenosed rats. When intravenously infused at the rate of 1.62 x 10(-11) mol/kg per min, the parathyroid hormone lowered portal pressure (15.1 +/- 0.7 vs. 14.0 +/- 0.8 mmHg) without affecting systemic blood pressure. With the portal vein isolated, the parathyroid hormone shifted the dose-response curves of KCl and acetylcholine to the right. However, the vasodilator effect of the parathyroid hormone was significantly less in portal hypertensive rats (EC50 of KCl increased 129.2% and acetylcholine 199.3%), compared to sham-operated rats (EC50 of KCl increased 158.7% and acetylcholine 270.2%). Similar results were found for the vasodilator action of verapamil (10(-9)-10(-6) M). On the other hand, the vasodilator effect of forskolin was similar for both groups. These results suggest that decreased responsiveness to the parathyroid hormone may be associated with calcium utilization by vascular smooth muscles.
Animals↗
Combined effect of dietary calcium and calcium antagonists on blood pressure reduction in spontaneously hypertensive rats.
Calcium supplementation and calcium channel blockers are known to have antihypertensive effects in similar subsets of hypertensive patients, as well as in spontaneously hypertensive rats (SHR). To investigate this apparent paradox, we placed 12-week-old SHR on one of three dietary levels of calcium (0.2, 0.4, or 0.8%), as well as on one of four doses of nifedipine (0, 50, 150, or 300 mg/kg food) for 8 weeks. We performed a similar experiment using four verapamil doses (0, 300, 900, or 1,800 mg/kg food). In the nifedipine experiment, two-way analysis of variance showed significant independent antihypertensive effects of both nifedipine (p less than or equal to 0.0001) and calcium (p less than 0.0001) and significant interaction (p = 0.0034), the latter suggesting a synergistic effect. In the verapamil experiment, both calcium and verapamil again had significant independent antihypertensive effects (p = 0.006 and p = 0.004, respectively), but there was no significant interaction. Although the effects of the calcium supplement or calcium antagonist alone were significant, such hypotensive responses were not optimal or predictable or clearly dose-dependent. However, the combination of a calcium supplement and calcium antagonist resulted in predictable or dose-dependent effects, and the optimal effect was reflected in the reduction of the SHR pressure to normal range for Wistar-Kyoto (WKY) rats. These results appear to indicate that supplementary calcium and calcium channel blockers act by different mechanisms in lowering blood pressure (BP), and that the combination of those differing mechanisms of action may have potential therapeutic benefit.
Animals↗
Tetrandrine inhibits both T and L calcium channel currents in ventricular cells.
Tetrandrine, a putative Ca2+ channel blocker, is extracted from the Chinese medicinal herb, Radix stephania tetrandrae. In the present study, the whole-cell version of the patch clamp technique was used to investigate the effects of tetrandrine on both T and L calcium channel currents in primary cultured neonatal rat ventricular cells. We show that tetrandrine inhibits both T and L calcium channel currents in ventricular cells. This inhibition of inward Ca2+ currents is concentration dependent and reversible. Tetrandrine does not shift the I-V relationship of the calcium currents. These results clearly demonstrate that tetrandrine acts as a calcium channel antagonist in ventricular cells. Previous data show that tetrandrine may be regarded as a wide-spectrum calcium channel antagonist.
Alkaloids↗
Calcitonin gene related peptide relaxes cholecystokinin-induced contraction in guinea pig gallbladder strips in vitro.
Calcitonin gene related peptide has been shown to relax vascular and intestinal smooth muscle. This study examines the effects of calcitonin gene related peptide on cholecystokinin-induced contraction of guinea pig gallbladder strips in vitro. Calcitonin gene related peptide was found to cause a dose-dependent relaxation of cholecystokinin-induced tension, which was blocked by the calcitonin gene related peptide receptor antagonist human calcitonin gene related peptide. Previous studies demonstrated that calcitonin gene related peptide acted directly on guinea pig gallbladder smooth muscle to inhibit acetylcholine- or KCl-induced contraction. The present results further confirm that calcitonin gene related peptide acts directly on the smooth muscle. In addition, the use of L-NG-nitroarginine methyl ester, glibenclamide, and other agents strongly suggests that calcitonin gene related peptide also acts by way of the nonadrenergic noncholinergic nervous system, to induce the relaxation of cholecystokinin-induced contraction observed in the guinea pig gallbladder strips.
Animals↗
Parathyroid function in hypertension.
PHF, secreted by the PTG, induces hypertension by increasing vascular smooth muscle calcium uptake and thereby increasing intracellular calcium levels. PHF secretion is inhibited by dietary calcium and the effects of PHF are blocked by calcium channel antagonists. This explains the paradox whereby both calcium and calcium channel blockers may be effective antihypertensive agents. PHF may be secreted by a specific cell type in the parathyroid gland, numbers of which seem to correlate with PHF levels. Thus, the parathyroid gland does seem to play a role in some forms of hypertension, but this role is probably not due to its production of PTH, but may be related to the secretion of the new factor--PHF.
Animals↗
Bay K-8644 in different solvents acts as a transient calcium channel antagonist and a long-lasting calcium channel agonist.
This report describes the effect of Bay K-8644 dissolved in various solvents on two types of calcium channel currents in neuroblastoma cells. Transient calcium channel (T channel) currents were not affected by Bay K-8644 dissolved in ethanol (EtOH) or polyethylene glycol (PEG). However, at the same concentration of 0.6 microM, Bay K-8644 dissolved in dimethylsulfoxide (DMSO) (Bay K-8644/DMSO) decreased the T channel current by 50%. The concentration of all three solvents in the bath was fixed at 0.3% to reach different final concentrations of Bay K-8644. At this fixed solvent concentration, the inhibitory effect of Bay K-8644/DMSO on T channel currents was dose-dependent; the solvents alone did not have any effect on T channel currents; and DMSO pretreatment of cells did not render the T channel current sensitive to Bay K-8644 dissolved in EtOH or PEG. Bay K-8644/DMSO was dried using a flash evaporator and redissolved in EtOH or PEG. Dried Bay K-8644 that was redissolved in EtOH or PEG to achieve a final concentration of 0.6 microM inhibited T channel currents by 39 or 35%, respectively. Furthermore, Bay K-8644 (10 nM) increased L channel currents by 80% with DMSO, but only 30% with EtOH as the solvent. These results show that in neuroblastoma cells Bay K-8644/DMSO, within the concentration range examined, is a T channel antagonist and more effective L channel agonist than Bay K-8644 dissolved in the two other solvents.
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
Purification of parathyroid hypertensive factor from plasma of spontaneously hypertensive rats.
Parathyroid hypertensive factor (PHF) is a newly described hypertensive factor that may be related to elevation of blood pressure in 30-40% of North American essential hypertensive patients. PHF is also found in several animal models of hypertension, including spontaneously hypertensive rats, and deoxycorticosterone acetate salt hypertensive rats. Plasma collected from spontaneously hypertensive rats (SHR) was used in the present study for purification of PHF. Plasma was dialyzed at a molecular mass cutoff of 1 kDa, and then ultrafiltered at a molecular mass cutoff of 5 kDa. PHF activity, as determined by bioassay (characteristic delayed hypertensive response in normotensive rat) was retained in the fraction that was greater than 1 kDa and less than 5 kDa. Dialyzed and ultrafiltered SHR plasma was fractionated by molecular-exclusion chromatography, either with Bio-Gel P-6 liquid chromatography, or TSK 2000 SW HPLC. The biological activity was detected in a discrete region corresponding to a molecular mass of 2.5-3 kDa. When the molecular-exclusion fraction was subsequently fractionated by reverse-phase HPLC, biological activity was located in a single discrete peak, which did not occur in plasma from normotensive rats prepared in a similar manner. The biologically active fraction of PHF was inactivated by trypsin; this and its UV spectrum indicate the presence of a peptide structure.
Animals↗
The effects of parathyroid hormone on L-type voltage-dependent calcium channel currents in vascular smooth muscle cells and ventricular myocytes are mediated by a cyclic AMP dependent mechanism.
The present study demonstrated that L channel currents were decreased in smooth muscle cells, and increased in ventricular myocytes by both bovine parathyroid hormone, (bPTH-(1-34)), and dibutyryl cyclic AMP (db-cAMP), using the whole cell version of the patch clamp technique with Ba2+ as the charge carrier. The effects of bPTH-(1-34) and db-cAMP on L channel currents were additive but not synergistic. Furthermore, the effects of bPTH-(1-34) on L channel currents in these 2 cell preparations were abolished in the presence of a cAMP antagonist. These results suggest that the effects of bPTH-(1-34) on L channel currents in vascular smooth muscle cells and ventricular myocytes are mediated by a cAMP-dependent mechanism.
Animals↗
Regulation of secretion of the teleost fish hormone stanniocalcin: effects of extracellular calcium.
The release in vivo and in vitro of stanniocalcin (STC) from the corpuscles of Stannius (CS) of the rainbow trout and the European eel was studied. Intraperitoneal injection of CaCl2 (2.45 mmol.kg-1 fish) leads to an elevation of both ionic and total calcium in the plasma and results in the release of STC from the CS into the blood. Release of STC in vitro is not affected at "physiological" (1.0-1.5 mM) or lower Ca2+ levels in the incubation medium. High levels of Ca2+ (2.5 mM and higher), however, stimulate the release of STC, in particular that of stored STC. We hypothesize that variations in extracellular Ca2+ in the normocalcaemic range do not directly regulate STC release.
Animals↗
The loss of 45Ca2+ associated with prolactin release from the tilapia (Oreochromis mossambicus) rostral pars distalis.
The relationship between tritium 3H-labeled prolactin (PRL) release and the loss of tissue-associated 45Ca2+ was examined in the tilapia rostral pars distalis (RPD) using perifusion incubation under conditions which inhibit or stimulate PRL release. Depolarizing [K+] (56 mM) and hyposmotic medium (280 mOsmolal) increased both the release of [3H]PRL and the loss of 45Ca2+. The responses to high [K+] were faster and shorter in duration than those produced by reduced osmotic pressure. The depletion of Ca2+ from the incubation medium with 2 mM EGTA suppressed the [3H]PRL response evoked by high [K+] or reduced osmotic pressure. Exposing the tissues to Ca(2+)-depleted medium in the absence of high [K+] or reduced osmotic pressure produced a sharp, but brief, increase in 45Ca2+ loss. Cobalt (10(-3) M), a competitive inhibitor of calcium-mediated processes, inhibited the [3H]PRL response to hyposmotic medium and to high [K+]. Cobalt also diminished the increased loss of 45Ca2+ evoked by exposure to reduced osmotic pressure, but was ineffective in altering responses to high [K+]. Methoxyverapamil (D600; 10(-5) M), a blocker of certain voltage-sensitive Ca2+ channels, did not alter either the [3H]PRL or the 45Ca2+ responses to high [K+] and reduced osmotic pressure. Taken together with our earlier studies, the present findings suggest that exposure to high [K+] or hyposmotic medium produces rapid changes in the Ca2+ metabolism of the tilapia RPD that are linked to the stimulation of PRL secretion. Nevertheless, the increased 45Ca2+ loss, but not [3H]PRL release, upon exposure to Ca(2+)-depleted media suggests that Ca2+ loss may not always reflect intracellular events that lead to PRL release.
Animals↗