GTP gamma S activates calcium channels in neonatal rat ventricular cells.
Explore the source record for details and available documents.
Action Potentials↗
Biomedical subjects
C G Benishin
Publications and source records attributed to C G Benishin.
Actions of ginsenoside Rb1 on choline uptake in central cholinergic nerve endings.
The ginsenoside Rb1 has previously been reported to improve memory deficits induced by anticholinergic drug treatment, and to facilitate acetylcholine (Ach) release from rat brain hippocampal slices. The increase in ACh release was not associated with an increase in calcium uptake into nerve terminals, but was associated with an increase in uptake of the precursor choline. In the present studies, analysis of choline uptake kinetics indicated that Rb1 increased the maximum velocity of choline uptake, while the affinity of the choline uptake carrier for choline (Km) was not significantly altered. Acute treatment with Rb1 did not alter the number of [3H]hemicholinium-3 (HC-3) binding sites in any of three cholinergic brain regions examined, suggesting that the increase in the maximum velocity of choline uptake was not associated with an increase in the number of choline carriers. However, chronic (3 day) administration of Rb1 did increase the number of choline uptake sites in the hippocampus, and to a lesser extent in the cortex.
Acetylcholine↗
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↗
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↗
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↗
Parathyroid hypertensive factor, a circulating factor in animal and human hypertension.
A new circulating hypertensive factor (parathyroid hypertensive factor; PHF) was shown to exist in the plasma of spontaneously hypertensive rats (SHR) but not in that of normotensive rats. PHF produced a delayed increase in blood pressure with a peak response at 45 min (bolus injection) or 60 to 90 min (continuous infusion). This increase in blood pressure was coupled with an in vitro increase in calcium uptake in rat tail artery with a similar time course. The involvement of calcium in the mechanism of action was supported by the inhibitory effect of calcium antagonists on the vascular action of PHF. Furthermore, PHF increased the intracellular free calcium concentration in cultured smooth muscle cells from rat tail artery. Parathyroidectomy and parathyroid transplant experiments indicated the parathyroid origin of PHF. A culture of parathyroid glands from SHR, but not from normotensive rats, produced in the medium a factor which has the same biological property and HPLC retention time as plasma PHF. A novel cell type was described in the parathyroid gland of SHR, but not normotensive rats, and the percent of these cells correlated significantly with plasma PHF level and blood pressure. In some hyperparathyroid patients, plasma PHF and hypertension were found, both of which disappeared after surgical removal of the parathyroid gland. In both animal models and human studies, PHF seems to be associated with low or normal plasma renin and salt-sensitive type of hypertension.
Animals↗
Calcitonin gene-related peptide: an inhibitor of guinea pig gallbladder contraction.
Calcitonin gene-related peptide (CGRP) relaxes vascular and intestinal smooth muscle. This study localized CGRP in the guinea pig gallbladder, examined the effects of CGRP on KCl- and ACh-induced contraction, and determined CGRPs site of action in the gallbladder. The gallbladder of male Hartley guinea pigs was used in in vitro tension studies, radioimmunoassay, or immunocytochemical studies. Radioimmunoassay showed that 8.0 +/- 0.5 pmol/g of immunoreactive CGRP was present. Immunocytochemistry demonstrated that immunoreactive-CGRP nerve fibers occurred around blood vessels, in gallbladder smooth muscle layers, and were associated with ganglia. No immunoreactive cell bodies were observed, even after colchicine treatment. The in vitro tension studies showed that CGRP inhibits either KCl- or acetylcholine-stimulated contraction. CGRP may in part act directly on the gallbladder smooth muscle to inhibit contraction.
Acetylcholine↗
Effects of ginsenoside Rb1 on central cholinergic metabolism.
Ginsenosides, the saponins of ginseng, are bioactive ingredients which exert many beneficial effects. One ginsenoside, Rb1, extracted from North American ginseng (Panax quinquefolium L.), partially prevents the memory deficits induced by a cholinergic agent (scopolamine) in rats. In vitro studies show that Rb1 has no effect on quinuclidinyl benzylate binding or on acetylcholinesterase activity, but facilitates the release of acetylcholine (ACh) from hippocampal slices. The increase in ACh release is associated with an increased uptake of choline into nerve endings; however, calcium influx is unaltered. The ability of Rb1 to prevent memory deficits may be related to facilitation of ACh metabolism in the central nervous system.
Acetylcholine↗
Parathyroid glands and cardiovascular functions.
Explore the source record for details and available documents.
Animals↗
Effects of calcitonin gene-related peptide on longitudinal muscle and myenteric plexus of guinea pig ileum.
Effects of rat calcitonin gene-related peptide (rCGRP) on the longitudinal muscle-myenteric plexus (lm-mp) have been investigated in the present study. rCGRP was shown to have a biphasic effect on the nonstimulated lm-mp, i.e., a transient contraction followed by a longer lasting relaxation. This biphasic action was dose-dependent over the concentration range of 10(-10) to 10(-5) M. Tetrodotoxin (1 microM), atropine (1 microM), 2-chloroadenosine (1 microM) and clonidine (1 microM) inhibited the stimulatory effect. Tetrodotoxin and clonidine also partially inhibited the relaxing effect of rCGRP. This biphasic action of rCGRP was also seen on the contraction of the lm-mp elicited by electrical field stimulation. rCGRP showed only a relaxing effect on the nonstimulated plexus-free longitudinal muscle. rCGRP (2.6 x 10(-10) to 2.6 x 10(-7) M) inhibited both the phasic and tonic contractions induced by histamine in a competitive way and showed a more potent effect on the tonic contraction than that on the phasic contraction. rCGRP at the same dose range also inhibited the tonic but not phasic contraction evoked by membrane depolarization with the maximal stimulation of KCl (30 mM). rCGRP inhibited KCl-, but not histamine-induced, extracellular calcium-dependent contraction. The peptide did not affect the dose-response curve of oxotremorine. These results suggest that rCGRP may exert its stimulatory actions on the lm-mp via actions on the plexus nerves, whereas the depressant actions may be mediated via the nerves, as well as directly on the smooth muscle.
Animals↗
Control of calcium channels in neuroblastoma cells (N1E-115).
Neuroblastoma cells (N1E-115) were used as models of transient (T) and long-lasting (L) Ca++ channels. The whole cell version of the patch clamp technique was used to measure inward Ca++ currents, and the fluorescent indicator, Fura-2, was used to measure changes in intracellular Ca++. Cells were cultured and selected during recording so that predominantly T or L channel currents were measured. T channel currents did not respond to dihydropyridine or parathyroid hormone, whereas L channel currents did. BAY-K-8644 increased and nifedipine decreased L channel currents. After a 15 mM KCl challenge, cells with predominantly T channels responded with a transient change in intracellular Ca++, while cells with predominantly L channels showed a sustained response. PTH inhibited the increase in intracellular Ca++ in cells with L channels, but not in those with T channels. PTH may be an example of an endogenous calcium channel blocker, at least in neuroblastoma cells.
Calcium Channel Blockers↗
Specific inhibition of long-lasting, L-type calcium channels by synthetic parathyroid hormone.
The effect of an active synthetic N-terminal fragment of bovine parathyroid hormone (bPTH), bPTH-(1-34), on Ca2+ channels was studied in mouse neuroblastoma cells (N1E-115). With the whole-cell variation of the patch-clamp technique, T (transient) and L (long-lasting) types of Ca2+ currents were identified. Pharmacological characterization showed that the L current was amplified by the Ca2+ channel stimulator BAY K-8644, but the T current was unaffected. The administration of bPTH-(1-34) produced dose-related inhibition of the L current, which could be reversed by BAY K-8644. The peptide had no effect on the T current. In addition, use of the fluorescent indicator fura-2 showed that bPTH-(1-34) inhibited the KCl-stimulated increase in intracellular free Ca2+ in neuroblastoma cells with L channels but not in cells with T channels. An inactivated (oxidized) preparation of bPTH-(1-34) failed to affect the L current. High-affinity binding of labeled PTH analog to these neuroblastoma cells was also demonstrated. In addition, bPTH-(1-34) inhibited the L current in cultured vascular smooth muscle cells from rat tail artery. These data indicate that, in some tissues, PTH can act as an endogenous blocker of Ca2+ entry.
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
Purinergic modulation of hippocampal acetylcholine release involves alpha-dendrotoxin-sensitive potassium channels.
Modulation of acetylcholine (ACh) release from superfused hippocampal slices was examined when the release of ACh was stimulated by exposure of slices to elevated K+ concentration. Evoked release was not sensitive to inhibition by 0.1 microM tetrodotoxin, but it could be inhibited in a dose-dependent manner by a muscarinic agonist (10-100 nM oxotremorine) and a purinergic agonist (10-100 nM 2-chloroadenosine). The alpha-dendrotoxin (100 nM), which selectively blocks voltage-gated inactivating K+ channels in nerve endings, did not affect the release of ACh under resting or depolarized conditions. However, alpha-dendrotoxin reduced the 2-chloroadenosine-induced inhibition of release, but did not alter the oxotremorine-induced inhibition. These results suggest that an alpha-dendrotoxin-sensitive K+ channel may be activated as an obligatory step in the modulation of ACh release by presynaptic purinergic receptor activation, but not in the modulation by presynaptic muscarinic receptors.
2-Chloroadenosine↗
Parathyroid hypertensive factor.
A new circulating hypertensive factor, parathyroid hypertensive factor (PHF), has been demonstrated in the plasma of spontaneously hypertensive rats (SHR) but not in that of normotensive rats. PHF produced a delayed increase in blood pressure with a peak response after 45 min (bolus injection) or 60-90 min (continuous infusion). This increase in blood pressure was coupled with an in vitro increase in calcium uptake in the rat tail artery which had a similar time-course. The evidence that calcium is involved in the mechanism of action is supported by the inhibitory effect of calcium antagonists on the vascular action of PHF. Furthermore, PHF increased the intracellular free calcium concentration in cultured smooth muscle cells from the rat tail artery. Parathyroidectomy and parathyroid transplant experiments indicated that PHF originated in the parathyroid gland. Cultured parathyroid glands from SHR but not from normotensive rats produced a factor in the medium with the same biological property and retention time on high performance liquid chromatography as plasma PHF. A novel cell type was described in the parathyroid gland of SHR, but not normotensive rats, and the percentage of these cells was correlated significantly with the plasma PHF level and the blood pressure level. In some hyperparathyroid patients, plasma PHF and hypertension were both present, and both disappeared after surgical removal of the parathyroid gland. In both animal models and human studies, PHF seems to be associated with low or normal levels of plasma renin and the salt-sensitive type of hypertension.
Animals↗
Potassium channel blockade by the B subunit of beta-bungarotoxin.
beta-Bungarotoxin (beta-BTX) isolated from the venom of Bungarus multicinctus has previously been reported to be a neurotoxic protein. The toxin is composed of two subunit chains, denoted A and B. The intact toxin was first examined in this study for its ability to block central nerve ending K channels using the 86Rb efflux technique. beta-BTX, when preincubated with synaptosomes for 30 min in the absence of extracellular Ca2+, selectively inhibited the slowly inactivating voltage-dependent (S) component of 86Rb efflux. The EC50 for inhibition is 1 to 3 nM. The two subunit chains were separated and isolated by reduction and carboxymethylation of the parent toxin. The K channel-blocking activity was associated only with the reduced and carboxymethylated B-subunit of beta-BTX (RCM-B). The dose-dependent inhibition by RCM-B exhibited an apparent biphasic response, with the noninactivating voltage-gated K channel being more susceptible to RCM-B inhibition (EC50 = 0.1 to 0.3 nM) than to inhibition by the parent compound. Additionally, the inactivating voltage-gated K channel (T) was sensitive to inhibition by higher concentrations of RCM-B (EC50 = 1 to 3 nM). These results suggest that the B-chain of beta-BTX may be responsible for blockade of certain voltage-gated K channels in a manner that is not directly related to the known phospholipase activity of the intact molecule.
Animals↗
Acute hydrogen sulfide poisoning. Demonstration of selective uptake of sulfide by the brainstem by measurement of brain sulfide levels.
The possibility of measuring sulfide levels in the central nervous system (CNS) opens up many avenues for exploration. In acute hydrogen sulfide (H2S) poisoning, death results from loss of central respiratory drive. To date, however, measurement of brain sulfide has not been possible. By employing gas dialysis and ion chromatography coupled to electrochemical detection, rat brain sulfide levels could be measured either following inhalation of H2S or after injection of sodium hydrosulfide (median lethal dose, [LD50] = 14.6 +/- 1.00 mg/kg). Accumulation of brain sulfide was linearly proportional to the dose over the range 0.50 LD50 to 3.33 LD50 units, and was strongly correlated with mortality data (R = 0.947). Furthermore, analysis of untreated (control) brain showed an endogenous sulfide level of 1.57 +/- 0.04 micrograms/g (mean +/- SE; N = 16). Studies on various rat brain regions (brainstem, cerebellum, hippocampus, striatum and cortex) showed that the endogenous sulfide level of brainstem, 1.23 +/- 0.06 micrograms/g, was significantly lower than that of the other brain regions. Net uptake of sulfide was greatest in the brainstem (3.02 micrograms/g) compared to the other regions as was the selective accumulation of sulfide as calculated from normalized blood flow rates. The results of subcellular fractionation demonstrated that sulfide was detectable in fractions enriched in myelin, synaptosomes and mitochondria. Approximately one-quarter of the endogenous sulfide content of whole rat brain was found in the mitochondrial fraction. The sulfide content of these fractions increased 2- to 3-fold after 50 mg/kg NaHS, the greatest increases occurring in myelin- and mitochondrial-enriched fractions.
Analysis of Variance↗
Metal cations as synaptosomal calcium blockers in studies with Fura-2.
Metal ions are often used to block calcium channels in various tissues, including synaptosomes. In the present study, Fura-2 was used to determine the effectiveness of various metal ions as calcium channel blockers in rat brain synaptosomes in vitro. In buffer solutions, La3+ and Cd2+ increased the Fura-2 fluorescence in a manner similar to Ca2+. Ni2+ and Mn2+ appeared to be fluorescence quenching cations, and Sr2+ and Co2+ had little effect on the fluorescence of Fura-2. In suspensions of synaptosomes under resting conditions, Cd2+, Ni2+ and Mn2+ were found to be not suitable for use in synaptosome studies. On the other hand, La3+ and Co2+ had little effect on the Fura-2 fluorescence of resting synaptosomes, and under depolarizing conditions, La3+ and Co2+ decreased the Fura-2 fluorescence. These results, therefore, suggest that La3+ and Co2+ may be suitable as calcium channel blockers in synaptosome studies.
Animals↗
Guanine nucleotide binding proteins may modulate gating of calcium channels in vascular smooth muscle. I. Studies with fluoride.
Fluoride (F-), a known stimulator of G-proteins, was used to examine the relationship between G-proteins and calcium channels (CaC) in rat vascular smooth muscle (VSM). Treatment of isolated rat tail artery helical strips with F- (2.5-20 microM) produced a Ca++-dependent contraction. In the absence of added AlCl3, subthreshold NaF shifted the KCl, as well as the arginine vasopressin and norepinephrine concentration-related tension curves to the left. Nifedipine and verapamil, known CaC blockers, inhibited the NaF-related contraction. AlCl3 (20 microM), which is required for G-protein stimulation by F-, strikingly potentiated the contractile response to F-. The NaF-induced contraction was relaxed by 3-isobutyl-1-methylxanthine as well as by forskolin and by dibutyryladenosine-cyclic AMP, and the effect therefore may be independent of cAMP. 45Ca-uptake was elevated by NaF, and partially blocked by nifedipine and verapamil. NaF also inhibited the basal and forskolin-stimulated cAMP production, suggesting that F- stimulated the putative Gi in the intact VSM cells. NaF stimulated accumulation of IP in a concentration-dependent manner, indicating that F- stimulated the putative G-protein Gp which couples various receptors to hydrolysis of phosphoinositides and mobilization of Ca++. These results indicate that NaF-induced vasoconstriction is related to the opening of the CaC in the plasma membrane and perhaps a subsequent entry of the extracellular Ca++ into the cell.(ABSTRACT TRUNCATED AT 250 WORDS)
1-Methyl-3-isobutylxanthine↗