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C G Benishin

Publications and source records attributed to C G Benishin.

At least 19 recordsLinked to original sources
PubMed1998

Nitric oxide selectively inhibits intracellular Ca++ release elicited by inositol trisphosphate but not caffeine in rat vascular smooth muscle.

The present study was designed to investigate whether nitric oxide (NO) could interfere with intracellular Ca++ release through different pathways in vascular smooth muscle. Phasic contractions of rat aorta induced by phenylephrine or caffeine in Ca++-free solution were used as an indicator of intracellular Ca++ release through the inositol 1,4,5-triphosphate receptor pathway and the ryanodine receptor pathway, respectively. In addition, cytoplasmic Ca++ concentration ([Ca++]i) in vascular smooth muscle cells was determined by fluorescence measurement. Acetylcholine (ACh) inhibited the phenylephrine-evoked phasic contractions in Ca++-free solution in endothelium-intact but not -denuded aortic rings in a dose-dependent manner. However, ACh did not affect the action of caffeine. The inhibition by ACh was blocked completely by the NO synthase inhibitor Nomega-nitro-L-arginine, which could be reversed totally by L-arginine but not D-arginine. Methylene blue, a soluble guanylate cyclase inhibitor, also abolished the inhibition by ACh. Sodium nitroprusside, an NO donor, attenuated the phenylephrine- but not caffeine-induced phasic contractions in denuded aortic rings in Ca++-free solution. The effect of sodium nitroprusside was reversed substantially by methylene blue. Furthermore, sodium nitroprusside inhibited the elevation of [Ca++]i induced by phenylephrine in vascular smooth muscle cells isolated from rat aorta in the absence of extracellular Ca++, which could be abolished significantly by methylene blue. These results suggest that NO selectively inhibits intracellular Ca++ release stimulated by inositol 1,4,5-triphosphate, but not caffeine in vascular smooth muscle.

Animals↗
PubMed1996

Calcium mobilization and isometric tension in bovine tracheal smooth muscle: effects of salbutamol and histamine.

We determined if decreases in relative free intracellular calcium concentration ([Ca2+]i) caused by salbutamol, a selective beta2-adrenoreceptor agonist, were paralleled by calcium egression from the cytosol in bovine trachealis muscle strips. [Ca2+]i, or tissue-surface extracellular calcium changes (Ts[Ca2+]ext), were monitored using Fluo-3 acetoxymethylester or Fluo-3 pentaammonium salt simultaneously with isometric tension. Salbutamol (1 microM) decreased histamine-induced isometric tension from an average peak tension of 128.5 +/- 18.4 to -4.9 +/- 0.3 mN/mm2, and reduced the associated sustained increases in [Ca2+]i from 100% at peak to 20.4 +/- 7.6%. Both histamine-induced elevation in [Ca2+]i and isometric tension were reversed completely by forskolin (1 microM). In muscle strip at active resting tension, salbutamol caused a decrease (49.6 +/- 12.1%) in [Ca2+]i. Following precontraction with histamine, salbutamol caused an immediate and sustained increase in Ts[Ca2+]ext which was not seen in a Na(+)-free solution. Finally, propranolol (10 microM) blocked both increases in Ts[Ca2+]ext and muscle relaxation caused by salbutamol. These findings indicate that in bovine trachealis muscle, the effect of salbutamol to decrease [Ca2+]i and isometric tension is via a beta2-adrenoceptor, and the changes in [Ca2+]i are by an increase in calcium egression via the Na(+)/Ca2+ exchanger, and reuptake by myoplasmic stores.

Albuterol↗
PubMed1996

The actions of prostaglandin E2 on potassium currents in rat tail artery vascular smooth muscle cells: regulation by protein kinase A and protein kinase C.

In vascular smooth muscle cells (VSMCs) of rat tail artery, prostaglandin E2 (PGE2) inhibited a voltage-dependent, delayed rectifier K channel current (Ik). The inhibition was concentration-dependent, via a receptor-mediated mechanism involving the activation of G protein(s) (Ren et al., 1995). In this study, we show that the PGE2-induced inhibition of Ik was mediated by activation of protein kinase A (PKA) and possibly protein kinase C (PKC). Pretreatment of the cells with cyclic adenosine 3',5'-monophosphothioate Rp-isomer (Rp-cAMPs), an inhibitor of adenosine 3', 5'-cAMP-dependent protein kinase (PKA), almost completely abolished the PGE2-induced inhibition. Forskolin, dibutyryl cAMP (Db-cAMP) and cyclic adenosine 3',5'cyclic monophosphothioate Sp-isomer (Sp-cAMPs), activators of adenylate cyclase and PKA, mimicked the effect of PGE2 on Ik. Phosphodiesterase inhibition by 3-isobutyl-1-methylxanthine did not alter the PGE2-induced inhibition of Ik. Moreover, we also found that phorbol myristate acetate (PMA), a PKC activator, significantly suppressed Ik. Both the kinase inhibitor staurosporine and down-regulation of PKC by prolonged exposure of the cells to PMA blocked the PGE2-induced inhibition of Ik, but had no effects on the forskolin, Db-cAMP or SpcAMP-induced effect on Ik. Pretreatment of the cells with Rp-cAMPs only partially diminished the degree of Ik inhibition evoked by PMA. Assay of cAMP content indicated that both PGE2 and PMA induced cAMP accumulation. These results strongly suggest that the modulation of Ik by PGE2 in rat tail artery VSMCs involves signal transduction through both PKA and PKC activation. The activation of PKC may potentiate the cAMP-PKA stimulation, whereas the cAMP-PKA cascade did not seem to affect the PKC pathway. These observations suggest that "cross talk" between the two second-messenger systems is involved in the mechanisms that mediate the effect of PGE2.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Ability of some K+ channel blockers to reverse inhibition of electrically evoked contractions of longitudinal muscle-myenteric plexus.

Blockers selective for different potassium (K+) channels were examined for their ability to reverse inhibition of electrically evoked contractions of longitudinal muscle-myenteric plexus (lm-mp) by adenosine analogs. Cyclohexyl adenosine (CHA) was selected for these studies, since it effectively inhibited contraction (EC50 33 nM). 4-aminopyridine (4-AP) antagonized the inhibition by the adenosine analog, but also stimulated contraction by itself. alpha- and gamma-dendrotoxin produced the most profound reversal of CHA-induced inhibition, while producing a minimal contraction alone. Other blockers produced only nominal reversal of the CHA-induced inhibition. These results suggest that inhibition by CHA is mediated via activation of an alpha- and gamma-dendrotoxin-sensitive K+ channel.

4-Aminopyridine↗
PubMed1995

Effects of calcitonin gene-related peptide on cyclic AMP production and relaxation of longitudinal muscle of guinea pig ileum.

The effects of rat calcitonin gene-related peptide (rCGRP) on the content of cyclic nucleotides in the cells of plexus-free longitudinal muscle (LM) of guinea pig ileum relative to smooth muscle relaxation were investigated. In the absence of isobutyl-methyl-xanthine (IBMX), a nonspecific inhibitor of phosphodiesterases, rCGRP significantly increased cyclic 3'5'-adenosine monophosphate (cAMP) content that correlated temporally to the relaxation of the muscle. Cyclic 3'5'-guanosine monophosphate (cGMP) content was not affected by this peptide. IBMX potentiated both the increase in cAMP content and the muscle relaxation induced by rCGRP. rCGRP increased cAMP content in a concentration-dependent manner, with an ED50 value of 7.5 x 10(-9) M. Both the rCGRP-stimulated increase in cAMP content and the rCGRP-induced muscle relaxation were blocked by hCGRP(8-37), a selective antagonist of CGRP receptors. The pA2 value of hCGRP(8-37) for rCGRP-induced inhibition of tension was calculated to be 6.48. These results suggest that CGRP relaxes the LM through its specific receptors and involves the generation of cAMP, but not the generation of cGMP.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Effects of calcitonin gene-related peptide on intracellular calcium concentration in longitudinal muscle of guinea pig ileum.

The effect of rat calcitonin gene-related peptide (rCGRP) on intracellular free calcium concentration ([Ca2+]i) and its relationship with muscle relaxation were examined in plexus-free longitudinal muscle (LM) of the guinea pig ileum using a [Ca2+]i-tension simultaneous recording technique. Tissue was stimulated with either histamine (0.5 microM) or KCl (30 mM). rCGRP at a concentration of 263 nM (which displayed maximal relaxation of the LM) caused a small and brief but significant decrease in the [Ca2+]i in histamine-treated tissue. On the other hand, the same concentration of rCGRP relaxed the muscle without affecting the [Ca2+]i in KCl-treated tissue. rCGRP caused a dissociation between the changes in [Ca2+]i and tension. The effects of forskolin 0.5 microM) and nifedipine (10 nM) on both [Ca2+]i and tension were examined in comparison with rCGRP. Forskolin lowered the tension to greater extent than the [Ca2+]i whereas nifedipine (10 nM) diminished both the [Ca2+]i and tension in a parallel manner in histamine-treated tissues. These results suggest that rCGRP may not reduce [Ca2+]i as its primary mechanism of relaxation and it may change the calcium sensitivity of the contractile elements of the smooth muscle.

Animals↗
PubMed1995

Prostaglandin E2 contracts vascular smooth muscle and inhibits potassium currents in vascular smooth muscle cells of rat tail artery.

There is evidence to suggest that PGE2 plays an important role in the regulation of vascular smooth muscle tone. To determine the cellular basis of this action, we studied the effect of PGE2 on force in helical muscle strips from rat tail artery. PGE2 evoked a sustained contractile response. The contractile response was concentration-dependent, with an EC50 value of 9.6 microM. Patch-clamp studies were conducted to investigate the effects of PGE2 on K channels in isolated vascular smooth muscle cells from rat tail artery. Current-clamp studies showed that PGE2 (1 microM) depolarized the membrane by 15.9 +/- 1.3 mV. Under voltage-clamp conditions, a voltage-dependent, delayed outward rectifier K current was generated by stepwise depolarization from a holding potential of -80 mV. The current, which was activated at -45 to -40 mV and showed almost no inactivation, was inhibited by 45% using 10 mM TEA. PGE2 inhibited the outward K current in a concentration-dependent manner, with EC50 values of 3.5 microM and 4.9 microM in primary and subcultured cells, respectively. The PGE2 receptor antagonist sodium meclofenamate abolished the PGE2-induced K current inhibition. Furthermore, the intracellular application of guanosine 5'-O(-)[2-thiodiphosphate] (GDP beta S), a G protein inhibitor, and pretreatment of the cells with cholera toxin prevented the PGE2-induced inhibition, whereas application of pertussis toxin did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

K+ channel openers relax longitudinal muscle of guinea pig ileum.

The plexus-free longitudinal muscle was used to investigate the muscle-relaxing effects of the known K+ channel openers, cromakalim, pinacidil and nicorandil, and compared with other known muscle relaxants, calcitonin gene-related peptide (CGRP) and isoprenaline. The three K+ channel openers all decreased basal tension and inhibited the tonic tension evoked by 30 mM KCl, 0.5 microM histamine or 0.1 microM oxotremorine in a dose-dependent manner. The order of potency is cromakalim > pinacidil > nicorandil in KCl or oxotremorine-precontracted muscle strip and nicorandil > cromakalim > pinacidil in histamine-precontracted muscle strip. Inhibition by cromakalim was completely reversed by glibenclamide, a blocker of ATP-sensitive K+ channels, while inhibition by nicorandil or pinacidil was only partially antagonized. The tonic tension evoked by KCl, histamine or oxotremorine was relaxed by CGRP or isoprenaline. Inhibition by neither of these compounds was relieved by glibenclamide. These results suggest that while ATP-sensitive K+ channels may be present in the longitudinal muscle cells, they may not be involved in the actions of CGRP or isoprenaline on the longitudinal muscle.

Animals↗
PubMed1994

Evidence that prostaglandin E2 can block calcium-activated 86Rb efflux from rat brain synaptosomes via a protein kinase C-dependent mechanism.

The effects of prostaglandin E2 (PGE2) on 86Rb efflux from rat brain synaptosomes were studied to explore its role in nerve ending potassium (K+) channel modulation. A selective dose-dependent inhibition of the calcium-activated charybdotoxin-sensitive component of efflux was found upon application of PGE2. No significant effect was seen on basal and voltage-dependent components over the concentration range of 10(-8) to 10(-5) M. The protein kinase C (PKC) inhibitors H-7 (10 microM) and staurosporine (100 nM), as well as prolonged preincubation (90 min) with 4 beta-phorbol 12,13-dibutyrate, which has been reported to down-regulate PKC, abolished the PGE2-induced inhibition, whereas HA1004 (10 microM) and Rp-3',5'-cyclic phosphorothioate (100 nM), which are relatively more selective for protein kinase A than PKC, did not. 4 beta-Phorbol 12,13-dibutyrate (100 nM), an activator of PKC, produced a similar inhibition of the Ca(2+)-dependent component of 86Rb efflux but also had no effect on the basal and voltage-dependent components. These data suggest that PGE2 can inhibit rat brain nerve ending calcium-activated 86Rb efflux, and this inhibition may involve PKC activation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1994

PHF: the new parathyroid hypertensive factor.

Parathyroid Hypertensive Factor (PHF) was discovered in SHR rats as a circulating substance with a unique delayed (60-90 min) hypertensive effect when injected into a normotensive assay rat. Subsequently, this correlation with hypertension was established in humans, especially in low-renin, salt-sensitive patients. Animal model studies also confirmed this correlation. Endocrinectomy and glandular replacement studies suggested that the parathyroid gland was the source of PHF. Subsequently, glands and cells in culture were also shown to secrete the substance. Other studies verified the parathyroid origin of PHF. The mechanism of action of PHF was shown to rely mainly on the opening of L-type calcium channels in vascular smooth muscle cells with an increase in [Ca2++]i. It is known that diseases other than hypertension often show increased [Ca2++]i and clinical features similar to hypertension, among them Type II diabetes. A recent study shows a correlation between circulating PHF level and Type II diabetes irrespective of the blood pressure status of the patient. It is suggested that PHF may be a [Ca++]i modulator, an excessive amount of which in the circulation may act on various target tissues, resulting in various disease symptoms with hypertension as an example. There may be many other such PHF-related diseases yet to be identified.

Animals↗
PubMed1994

Mechanism of the vascular action of parathyroid hypertensive factor.

The present studies investigated the effect of parathyroid hypertensive factor (PHF) on intracellular calcium regulation in VSMC. Nifedipine inhibited the hypertensive effect of PHF in Sprague-Dawley (SD) rats in vivo. PHF amplified the L-type calcium current in vascular smooth-muscle cells (VSMCs) isolated from SD rat tail artery. PHF potentiated the tension induced by norepinephrine (NE) in the presence of normal added CaCl2 and inhibited the tension dependent on Ca2+ release from intracellular calcium store(s) induced by NE in SD rat tail artery helical strips. PHF potentiated the intracellular free calcium concentration ([Ca2+]i) increment induced by KCl in cultured VSMCs from SD rat tail artery. All of the in vitro cellular calcium effects of PHF temporally correlated with its delayed hypertensive effect in vivo. PHF did not affect the accumulation of inositol phosphates in SD rat tail artery. Infusion of theophylline blunted the hypertensive effect of PHF in SD rats, suggesting that PHF may stimulate phosphodiesterase (PDE) activity. We suggest that PHF may potentiate the effects of other vasoconstrictors on calcium channels and increase [Ca2+]i, which would then lead to an increase in the responsiveness of the VSMC to other vasoconstrictors, and therefore an increase in blood pressure. The action of PHF may involve stimulation of PDE activity.

Animals↗
PubMed1994

Clinical aspects of parathyroid hypertensive factor.

To determine the clinical significance of parathyroid hypertensive factor (PHF), physiological studies previously performed in animal models of hypertension were parallelled by human studies. These studies revealed that PHF-like activity is present in human hypertension, where it correlates with the salt-sensitive, low-renin state. As in spontaneously hypertensive rats, both supplemental calcium and calcium-channel blockers appear to be useful in the treatment of PHF-related hypertension. In primary hyperparathyroid patients, PHF presence is linked with the presence of hypertension. Postparathyroidectomy blood pressure falls in parallel with PHF levels. These preliminary human studies suggest that PHF may be a useful marker in the treatment of hypertension.

Animals↗
PubMed1994

Purification and structural characterization of parathyroid hypertensive factor.

Parathyroid hypertensive factor (PHF) has been purified from two sources of material: plasma of spontaneously hypertensive rats (SHRs) and culture medium from organ culture of SHR parathyroid glands. Chromatographic characteristics of PHF from these two sources are identical. Biological activity of PHF (assayed as the characteristic delayed hypertensive response in normotensive rats) is sensitive to degradation by treatment in base, and the enzymes trypsin, chymotrypsin, phospholipase C, and phospholipase D. PHF activity may also be extracted from source material with chloroform: methanol (4:1). A hypothetical structure for the active component of PHF is suggested. This is comprised of a peptide liked to a lysophospholipid.

Animals↗
PubMed1994

Inhibition of a K+ current by beta-dendrotoxin in primary and subcultured vascular smooth muscle cells.

beta-Dendrotoxin (beta-DTX), a polypeptide component of Eastern Green Mamba snake venom, inhibits a slow voltage-activated 86Rb efflux from synaptosomes, suggesting that beta-DTX inhibits K+ channels. The effects of beta-DTX on the K+ currents in primary cultured and subcultured (passages 8-12) rat tail artery vascular smooth muscle cells (VSMCs) were studied using the whole-cell patch-clamp technique. A delayed rectifier K+ current was observed in both types of cells. The current, which was relatively insensitive to tetraethylammonium, was activated at -40 to -30 mV and showed almost no inactivation. beta-DTX (1-1000 nM) decreased the outward K+ current. The effect was concentration dependent and reversible by washout but did not depend on the frequency of stimulation (use dependence) or the membrane potential. beta-DTX was more effective in primary cultured cells than in subcultured cells. K+ channels in primary cultured cells were maximally (45%) inhibited by 1 microM beta-DTX compared with 35% inhibition in subcultured cells. The concentration producing half-maximal inhibition was 5.1 x 10(-8) M for primary cells and 7.1 x 10(-8) M for subcultured cells. The delayed rectifier current was not affected by alpha-DTX, a blocker of the fast-inactivating outward K+ current (IA). These results clearly demonstrate that beta-DTX is a novel antagonist of the delayed rectifier K+ current in primary and subcultured rat tail artery VSMCs.

Animals↗
PubMed1994

Clinical aspects of parathyroid hypertensive factor.

Parathyroid hypertensive factor (PHF) in rats: PHF is an endogenous hypertensive substance which was originally associated with hypertension in spontaneously hypertensive rats (SHR). In this model, PHF was shown to act by increasing intracellular calcium levels in vascular smooth muscle and was linked with a characteristic pattern of abnormalities in overall calcium regulation. The action of PHF was blocked by calcium antagonists, suggesting that the effect of PHF was to increase extracellular calcium uptake. In SHR the parathyroid glands were shown to be the site of PHF secretion. This secretion was inhibited by an increase in dietary calcium. PHF was further shown to be unique to low-renin forms of hypertension, that is, those forms of hypertension characterized by abnormalities in calcium metabolism. PHF in humans: PHF was subsequently found in human low-renin salt-sensitive hypertension. As in SHR, calcium supplementation can lower PHF levels in humans. Similarly, there is circumstantial evidence for the parathyroid origin of PHF in humans. In human hypertensive patients, the presence of PHF has been shown to predict a favorable therapeutic response to calcium channel blockade. Recently, many of the abnormalities in calcium metabolism present in low-renin hypertension have also been described in other disease states. Notable among these diseases is non-insulin dependent diabetes mellitus. A survey of human non-insulin dependent diabetes mellitus has revealed that PHF was present in a disproportionate number of these patients independently of the blood pressure level. The significance of this latter finding needs to be explored, but PHF may prove to have relevance in diseases other than hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Identification and purification of parathyroid hypertensive factor from organ culture of parathyroid glands from spontaneously hypertensive rats.

Parathyroid hypertensive factor (PHF) is a newly described hypertensive factor isolated from the plasma of spontaneously hypertensive rats (SHR). Recent studies have suggested that the primary origin of PHF is the parathyroid gland (PG). In the present investigation, PG from spontaneously hypertensive rats (SHR), as well as from normotensive rats, were isolated and maintained in culture. The PG from SHR, but not normotensive rats, released PHF into the culture medium. Omission of calcium from the culture medium stimulated the release of PHF. For purification of PHF, parathyroid gland culture medium (PGCM) was first dialyzed at 1000 mwco, and then ultrafiltered at 5000 molecular weight cut-off (mwco). PHF activity was retained in the fraction that was greater than 1000 daltons and less than 5000 daltons. Dialyzed and filtered SHR PGCM was fractionated by molecular exclusion HPLC. Biologically active PHF was collected in a discrete region. The biologically active molecular exclusion fraction was subsequently fractionated by reverse-phase HPLC (C-8). PHF was collected in a single discrete peak, which did not occur in culture medium prepared from normotensive PG in a similar manner. This biologically active peak occurred in the same position on molecular exclusion and reverse-phase HPLC as PHF purified from SHR plasma using similar procedures. Incubation of PGCM with trypsin inactivates the biological activity of PHF. The UV spectrum of PGCM PHF is identical to that obtained from purified plasma PHF. These results are consistent with the presence of a peptide moiety in PHF, and support the parathyroid origin of plasma PHF.

Animals↗
PubMed1993

Production of polyclonal antisera to parathyroid hypertensive factor from spontaneously hypertensive rats.

OBJECTIVE: Parathyroid hypertensive factor (PHF) is a newly described hypertensive factor which may cause elevation of blood pressure in approximately 40% of North American essential hypertensive patients. PHF is also found in several animal models of hypertension, including spontaneously hypertensive rats (SHR), deoxycorticosterone acetate-salt hypertensive rats and salt-sensitive Dahl rats. The objective of the present study was to raise an antibody to PHF, and to use this antibody to study the effect of PHF in SHR. DESIGN: Plasma and parathyroid gland culture media collected from SHR were used in the present study as the antigen in the production and analysis of a polyclonal antiserum to PHF. METHODS: PHF is of low molecular weight (approximately 3000 daltons) and is sensitive to inactivation by trypsin. We used PHF partially purified from parathyroid gland culture media as the antigen to inoculate mice. The substance was bound to aminophenyl thioether paper discs to make it more antigenic. The discs were then emulsified in Freund's adjuvant (complete for first inoculation, incomplete for subsequent inoculations) for intraperitoneal implantation. Production of anti-PHF antisera was monitored by enzyme-linked immunosorbent assay. RESULTS: Antisera produced in mice reacted with purified PHF prepared from SHR plasma as well as with PHF prepared from parathyroid gland culture media. PHF treated with the PHF antiserum produced no characteristic hypertensive response in normotensive assay rats. The antisera did not crossreact with two forms of bovine parathyroid hormone, bPTH (1-84), bPTH (1-34) or with shorter parathyroid hormone fragments, or with any other vasoactive substance tested. Injection of an aliquot of the antiserum in anesthesized spontaneously hypertensive rats reduced mean arterial pressure to a normal range of approximately 110 mmHg. CONCLUSIONS: These results indicate that (1) polyclonal antisera to PHF can be raised in mice and (2) PHF may contribute significantly to the elevated blood pressure in SHR.

Animals↗