Sequence and expression of mRNAs encoding the alpha 1 and alpha 2 subunits of a DHP-sensitive calcium channel

Complementary DNAs were isolated and used to deduce the primary structures of the alpha 1 and alpha 2 subunits of the dihydropyridine-sensitive, voltage-dependent calcium channel from rabbit skeletal muscle. The alpha 1 subunit, which contains putative binding sites for calcium antagonists, is a hydrophobic protein with a sequence that is consistent with multiple transmembrane domains and shows structural and sequence homology with other voltage-dependent ion channels. In contrast, the alpha 2 subunit is a hydrophilic protein without homology to other known protein sequences. Nucleic acid hybridization studies suggest that the alpha 1 and alpha 2 subunit mRNAs are expressed differentially in a tissue-specific manner and that there is a family of genes encoding additional calcium channel subtypes.

Renal pathology in von Hippel-Lindau disease

Von Hippel-Lindau disease, a rare autosomal disorder, is associated with multiple lesions, including a high incidence of renal lesions and CNS hemangioblastomas. Renal lesions have traditionally been classified as either benign cysts or solid renal cell carcinomas with or without cystic degeneration. We examined seven kidney specimens from four patients with von Hippel-Lindau disease. We found that renal cysts form a histopathologic continuum ranging from benign cysts (with one to two cell layers of bland epithelium), atypical cysts (demonstrating epithelial hyperplasia with or without mild cytologic atypia), to malignant cysts harboring renal cell carcinoma. The presence of atypia or foci of carcinoma does not correlate with cyst size. Lesions that appear radiologically or grossly solid range from conventional solid renal cell carcinoma, sometimes evidencing cystic degeneration, to lesions that are predominantly hyalinized, fibrotic nodules. In contrast to simple cysts occurring in the general population, which are virtually always benign, renal cysts in patients with von Hippel-Lindau disease may contain occult carcinoma. Radiologic evaluation, visual inspection at surgery, and even frozen section analysis of cyst lesions cannot be relied on to detect small foci of carcinoma. The spectrum of pathologic changes and the multicentricity of the renal lesions in von Hippel-Lindau disease complicate the radiologic evaluation and surgical management of these patients.

Effect of calcium channel modulators on isolated endothelial cells

Indirect evidence, using organic calcium channel modulators suggests that calcium channels exist in endothelial cells. Using freshly prepared and cultured bovine aortic endothelial cells, we have studied the effect of calcium channel modulators on Fura-2 fluorescence and have examined the binding of the dihydropyridine, (+)[3H]PN200-110. In both isolated primary and cultured cells, external calcium (0.5-2 mM) and bradykinin (10(-8) M) increased the intracellular calcium concentration. In cultured cells, the increase in calcium was not significantly attenuated by preincubation with nitrendipine (10(-8) M) or d-cis-diltiazem (10(-6) M). The calcium agonists (-)Bay k8644 and (+)202-791 had no effect on intracellular calcium concentration, but other agonists including ATP (10(-4) M) and thrombin (1.5 micrograms/ml) significantly increased the calcium concentration. Competition binding studies with (+)[3H]PN200-110 indicated specific binding of this ligand with a KD of 57 nM and a Bmax of 2.1 pmol/10(6) cells. While these data do not provide convincing evidence for the existence of calcium channels in cultured or fresh bovine aortic endothelial cells, explanations may yet reconcile our observations with the presence of calcium channels in these cells.

Characteristics of the phenylalkylamine binding site in canine cardiac sarcolemmal membranes

We have investigated the phenylalkylamine binding site in canine cardiac sarcolemmal preparations using (-)-[3H]-desmethoxyverapamil as the labeled ligand. Radioligand binding experiments were carried out in 10 mM Hepes (Na+) buffer and 1 mM EGTA, at pH 7.4 and 20 degrees C. A single high affinity binding site for (-)-[3H]-desmethoxyverapamil was identified both by saturation and competition binding experiments. Several phenylalkylamine derivatives such as (-)-D600, (+)-D600, verapamil and (+)-desmethoxyverapamil completely inhibited (-)-[3H]-desmethoxyverapamil binding with the following order of potency: (-)-desmethoxyverapamil greater than (-)-D600 greater than verapamil greater than (+)-desmethoxyverapamil = (+)-D600. In contrast to this, ronipamil, a new long acting phenylalkylamine derivative, produced only a 70% inhibition. Diltiazem also completely inhibited (-)-[3H]-desmethoxyverapamil binding to canine cardiac sarcolemma while nifedipine displaced only 70% of binding. (-)-[3H]-desmethoxyverapamil binding was also inhibited by Ca++ and Mg++. These data suggest the presence of a saturable, reversible and stereoselective phenylalkylamine binding site in canine cardiac sarcolemmal preparations which may be a receptor for the phenylalkylamine Ca++ channel inhibitors.

Stereoselective effect of diltiazem on endothelium-dependent relaxations in canine femoral arteries

Experiments were designed to analyze potential interactions between voltage-dependent calcium channel blockers and endothelium-dependent vascular responses. Rings of canine femoral artery were suspended for isometric force recording in organ chambers and contracted with prostaglandin F2 alpha. Removal of the endothelium had no effect on relaxations induced by d-cis-diltiazem (active stereoisomer), verapamil or nimodipine. When rings with endothelium were first partially relaxed with acetylcholine or the calcium ionophore A23187 the concentration-relaxation curve to d-cis-diltiazem (but not to verapamil or nimodipine) was significantly shifted to the right. Partial relaxation of femoral arterial rings without endothelium by sodium nitroprusside had no effect on relaxations evoked by diltiazem. Pretreatment with diltiazem (10(-6) M) had no effect on endothelium-dependent relaxations to acetylcholine in femoral artery rings. D-cis-Diltiazem partially reversed the relaxation induced by acetylcholine in a bioassay system, in which a ring of canine coronary artery without endothelium was superfused by solution passing through a segment of femoral artery with endothelium. D-cis-Diltiazem relaxed the bioassay ring when infused downstream of the perfused femoral artery with, or upstream of a femoral artery without endothelium. The effect of diltiazem was stereoselective (the less active l-cis-diltiazem had no effect). Verapamil did not reverse the relaxation induced by acetylcholine and did not affect the reversal induced by diltiazem. These findings indicate that diltiazem specifically antagonizes the production and/or the release of endothelium-derived relaxing factor(s) stimulated by acetylcholine or A23187 in canine femoral arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium Effects on Stomatal Movement in Commelina communis L. : Use of EGTA to Modulate Stomatal Response to Light, KCl and CO(2)

Stomatal movements depend on both ion influx and efflux; attainment of steady state apertures reflects modulation of either or both processes. The role of Ca(2+) in those two processes was investigated in isolated epidermal strips of Commelina communis, using the Ca(2+) chelator EGTA to reduce apoplastic [Ca(2+)]. The results suggest that a certain concentration of Ca(2+) is an absolute requirement for salt efflux and stomatal closure. EGTA (2 millimolar) increased KCl-dependent stomatal opening in darkness and completely inhibited the dark-induced closure of initially open stomata. Closure was inhibited even in a KCl-free medium. Thus, maintenance of stomata in the open state does not necessarily depend on continued K(+) influx but on the inhibition of salt efflux. Opening in the dark was stimulated by IAA in a concentration-dependent manner, up to 15.4 micrometer without reaching saturation, while the response to EGTA leveled off at 9.2 micrometer. IAA did not inhibit stomatal closure to the extent it stimulated opening. The response to IAA is thus consistent with a primary stimulation of opening, while EGTA can be considered a specific inhibitor of stomatal closing since it inhibits closure to a much larger degree than it stimulates opening. CO(2) causes concentration-dependent reduction in the steady state stomatal aperture. EGTA completely reversed CO(2)-induced closing of open stomata but only partially prevented the inhibition of opening.

Action of diltiazem on excitation-contraction coupling in bullfrog skeletal muscle fibers

In this study the calcium antagonist drug diltiazem was found to produce twitch potentiation, lower the mechanical threshold potential and block inward calcium currents in bullfrog skeletal muscle fibers. Under tonic conditions (stimulation either every 1 or 2 min) high concentrations of diltiazem were required to enhance twitch tension (ED50 = 249 microM) and block calcium currents (IC50 = 190 microM). In addition, 100 microM diltiazem lowered the mechanical threshold rheobase potential from -49.3 to -57.0 mV. At higher rates of stimulation, concentrations of diltiazem as low as 1 and 10 microM, which had no tonic action, were found to produce twitch potentiation and calcium channel block, respectively. Onset and washout of tonic and frequency-dependent actions of diltiazem on twitch and current amplitude occurred over a similar time course. It is proposed that the mechanical potentiation, as well as the calcium channel block produced by diltiazem, result from the interaction of diltiazem with the same or similar receptor site(s).

Usefulness of angioscopy in stenotic processes of the carotid--a comparison with morphological findings

The development of a new generation of ultrathin flexible fiberscopes permitted direct in-vivo intravascular visualization of pathological changes. But not until the construction of a double-lumen balloon catheter for simultaneous obstruction of the blood flow and rinsing of the vessel did an accurate percutaneous transluminal examination become possible. For testing the usefulness of angioscopic intraluminal diagnosis, 48 carotid arteries from 32 autopsies were examined independently by angioscopy and morphologically. There was a high degree of correspondence between the two methods, especially in cases with low-degree stenosis or complicated plaques, in which other examination methods often fail. Problems of underestimating fibrous plaques and optical projection upstream of the stenosis are discussed.

Roentgenographic underestimation of early asbestosis by International Labor Organization classification. Analysis of data and probabilities

We analyzed the limitations of the International Labor Organization (ILO) classification of chest roentgenograms in predicting the presence of histologically determined early asbestosis. The ILO system is arbitrary, without histologic correlates, and does not consider the asbestos exposure history or clinical and laboratory information. We present data from the literature and our own work which demonstrate that the application of the ILO classification to an asbestos-exposed individual can result in a 10 to 20 percent probability of a "normal" roentgenographic interpretation in the presence of significant asbestosis at the histologic level, leading to an inappropriate conclusion regarding the presence of asbestosis. In view of the data and statistical analysis presented, we suggest that sole reliance upon the ILO classified chest roentgenogram for determination of the presence of early pulmonary asbestosis in individual cases is inappropriate.

Guard cells of Commelina communis L. do not respond metabolically to osmotic stress in isolated epidermis: Implications for stomatal responses to drought and humidity

We investigated the hypothesis that stomatal aperture is regulated by epidermal water status. Detached epidermal peels of Commelina communis L. or leaf disks with epidermis attached were incubated in graded solutions of mannitol (0-1.2 M) containing KCl. In isolated epidermis, guard-cell solute content of open stomata did not decrease in response to desiccation. Guard cells of closed stomata accumulated solutes to the same extent in all levels of mannitol tested. There was no evidence of stress-induced hydroactive closure nor of inhibition of hydroactive opening, even when guard cells of closed stomata were initially plasmolyzed. Hydropassive, osmometer-like, changes in stomatal aperture in the isolated epidermis were induced by addition or removal of mannitol, but these did not involve changes in guard-cell solute content. In leaf disks, stomata exhibited clear hydroactive stomatal responses. Steady-state guard-cell solute content of initially open and initially closed stomata decreased substantially with increasing mannitol. Stomata were completely closed above approx. 0.4 M mannitol, near the turgor-loss point for the bulk leaf tissue. Stomata of Commelina did not exhibit direct hydroactive responses to environmental or epidermal water status. Stomatal responses to water deficit and low humidity may be indirect, mediated by abscisic acid or other signal metabolite(s) from the mesophyll.

A study of androgen-resistant subjects indicates that the 6.7 pI/56 kDa protein in genital skin fibroblasts is related to the androgen receptor

Two-dimensional gel electrophoresis of cultured human skin fibroblast lysates reveals a silver-stained "spot" of molecular mass 56 kilodaltons (kDa) and isoelectric point (pI) 6.7, occasionally as part of a doublet with a minor pI 6.5 partner. Its presence in each of 23 genital skin fibroblast strains (6 labium majus, 17 prepuce) and its absence in 30 of 32 control non-genital skin fibroblast strains accords with the 3-fold greater concentration of androgen-receptor activity in the former. However, the size and intensity of the spot do not change when cells are preincubated for 48 hours with 3 nM methyltrienolone (MT, a non-metabolizable androgen), and it is pulse-labeled with [35S]methionine to an autoradiographically equal extent, with or without incubation in 3 nM MT for 2 or 16 hours. Furthermore, the protein identified by the spot is found in the labium majus skin fibroblast strains from 2 of 12 unrelated subjects with complete androgen resistance due to negligible androgen-receptor activity, but it is absent from those of 2 others who have the same phenotype despite a normal level of qualitatively abnormal androgen-receptor activity. Hence, it is very unlikely to be an androgen-induced protein, and it cannot be a functional version of the androgen receptor itself. Its absence in 12 of 14 labium majus strains of subjects with complete androgen resistance, regardless of 5 alpha-reductase activities, indicates that it is neither a constitutive cytotypic marker of genital skin fibroblast differentiation nor a reflection of that enzyme. When intact prepuce fibroblasts are covalently labeled by photolysis with 50 nM [3H]MT, the only specific labeling detectable after two-dimensional electrophoresis is in the 6.7 and 6.5 pI doublet of the 56 kDa protein. Considering the sensitivity of silver staining and the incomplete concordance between the androgen-receptor activity of a strain and the size/intensity of its 6.7 pI/56 kDa spot on the gels, we postulate the latter to be a comparatively abundant androgen-binding protein that is causally related to the androgen receptor. The precise nature of this relation remains to be elucidated by use of novel immunologic and/or nucleic acid probes for this protein and for the mature androgen receptor. In any event, the presence or absence of the 6.7 pI/56 kDa protein in genital skin fibroblast lysates is a new marker of genetic heterogeneity within the class of complete androgen resistance.

Effects of isosorbide dinitrate and diltiazem on Ca2+ flux and contraction in artery

We studied the effects of isosorbide dinitrate and diltiazem on histamine-stimulated 45Ca fluxes and contractions of isolated porcine coronary artery. Isosorbide dinitrate was slightly more potent as an inhibitor of intracellular compared to extracellular calcium-dependent contraction. Isosorbide dinitrate inhibited histamine-stimulated calcium efflux and intracellular calcium-dependent contraction over similar concentration ranges. Isosorbide dinitrate partially inhibited histamine-stimulated calcium influx, but this effect was significant only at high concentration and correlated weakly with inhibition of contraction that was dependent on extracellular calcium. Diltiazem more potently inhibited extracellular vs. intracellular calcium-dependent contraction. Diltiazem partially inhibited histamine-stimulated calcium efflux and intracellular calcium-dependent contraction to similar extents (55-60%) and produced similar concentration-response relationships for inhibition of histamine-stimulated calcium influx and extracellular calcium-dependent contraction. The data suggest that alterations of cellular calcium metabolism are major mechanisms of vascular smooth muscle relaxation by isosorbide dinitrate and diltiazem, but that the specific alterations differ for the two drugs. Isosorbide dinitrate may inhibit contraction primarily by enhancing intracellular calcium sequestration, but possibly also by inhibiting agonist-stimulated calcium influx at high isosorbide dinitrate concentrations. Diltiazem primarily inhibits stimulated calcium influx, but may also inhibit intracellular calcium release.

Evaluation of surgical staples for ligation of the renal pedicle during nephrectomy

A mechanical stapling instrument was evaluated for ligation of the renal pedicle during nephrectomy in nine healthy sheep. Two forms of disposable loading unit, from which stainless steel surgical staples could be dispensed in double or triple staggered row configuration, were assessed for their proper function when applied across the renal pedicle singularly or in series. The response of the sheep to surgery was assessed by physical, hematological, and serum chemistry evaluations. Tissue healing was determined by gross and histopathological examinations. Ligation and transection of the pedicle took 2 to 4 minutes. The vessels of the pedicle ranged in diameter from 3 to 12 mm. In two sheep, overzealous stripping of perivascular tissue from the renal pedicle prior to placement of a triple staggered row of staples resulted in mild hemorrhage from the renal stump. This was controlled by placing a second triple staggered row of staples proximal to the first. It was concluded that ligation of the renal pedicle could be performed rapidly, effectively, and safely in healthy sheep using the correctly applied mechanical stapler. It is inferred that a similar technique would be applicable to other species including man.

Vasodilatory action of amlodipine on rat aorta, pig coronary artery, human coronary artery, and on isolated Langendorff rat heart preparations

Amlodipine inhibited contractions of rat aortic rings induced by 40 mM KCl (IC50 = 7.5 x 10(-9) M). The time to attain the maximum inhibitory effect of KCl-induced contractions was long (hours) and dependent on the concentration of amlodipine. After 6 h of washing in drug-free normal Krebs-Ringer solution the contractions recovered only partially. The KCl-induced contractions appeared to be more sensitive to inhibition by amlodipine than were norepinephrine-induced contractions. CaCl2-induced contraction of KCl-depolarized aortic rings was inhibited by amlodipine in a complex manner. Amlodipine not only increased ED50 but also inhibited the maximal tension induced by CaCl2. Amlodipine also inhibited 35 mM KCl-induced contractions of pig coronary artery rings (IC50 = 2.2 x 10(-8) M) and human coronary artery rings (IC50 = 2.1 x 10(-8) M). In Langendorff rat heart preparations, low concentrations of amlodipine increased coronary flow (ED50, 10(-9) M) whereas higher concentrations (greater than 10(-7) M) decreased coronary flow. Amlodipine also decreased the rate of contraction (+ dP/dt, IC50 = 3 x 10(-7) M) and the rate of relaxation (-dP/dt, IC50 = 1.2 x 10(-7) M). Amlodipine decreased heart rate but only at high concentrations (greater than 300 nM). The results of this study indicate that amlodipine is a potent vasodilator with similar cardiovascular actions to other dihydropyridines except that its effects are slower in onset and longer lasting.

[Lipid myopathy: a heterogenic familial case]

A case is reported of lipid storage myopathy in a 24-year-old patient and her family. In the patient and an aunt, muscle biopsy disclosed intrafibrillar lipid depositions, and electron microscopy revealed lipid vesicles in the sarcolemma border. In the father, no lipid depositions were observed but electron microscopy showed alterations to mitochondria compatible with a mitochondrial myopathy. In the patient muscular biochemistry revealed a major reduction in NADH oxydase activity and in the aunt a diminished level of carnitin compatible with carnitin deficiency. The heterogeneity of these lipidic myopathies is discussed.

Calcium channel activity in a purified dihydropyridine-receptor preparation of skeletal muscle

A purified dihydropyridine-receptor complex (DHPR) of skeletal muscle consisting of a major polypeptide of Mr 150K under reducing conditions induces divalent cation selective channels when incorporated into planar lipid bilayers. Channels were inserted into preformed planar bilayers by two techniques: (i) direct dilution of detergent-solubilized DHPR into the aqueous chambers adjacent to the bilayer membrane or (ii) reconstitution of DHPR into phospholipid vesicles followed by fusion of the preformed vesicles to the planar bilayer membrane. Unlike native membrane preparations of t-tubules, which only have one major Ca channel type of slope conductance of 12 pS in symmetrical 100 mM Ba, the purified DHPR complex induced at least two channel types with conductances of 12-14 and 22 pS. Some recordings suggest that these two channels are statistically coupled in time, i.e., that they may correspond to substrates of the same DHPR channel. Activity was found to occur spontaneously in the absence of the Ca channel agonist Bay k 8644. The 12-14-pS channel from DHPR exhibits voltage-dependent kinetics, is highly selective for barium ions, and was inhibited by micromolar nitrendipine. The 12-14-pS DHPR channel appears to be identical with functional Ca channels previously described in native t-tubules.

Identification of a novel 1,4-dihydropyridine- and phenylalkylamine-binding polypeptide in calcium channel preparations

A 1,4-dihydropyridine- and phenylalkylamine-binding polypeptide has been identified by photoaffinity labeling of purified rabbit and guinea pig skeletal muscle calcium channel preparations. The arylazide ligands (-)-[3H]azidopine and (-)-5-[(3-azidophenethyl)[N-methyl-3H]methylamino]-2-(3,4,5- trimethoxyphenyl)-2-isopropylvaleronitrile [( N-methyl-3H]LU 49888) were used to label 1,4-dihydropyridine- and phenylalkylamine-binding sites, respectively. A single, 155 to 170-kDa polypeptide was specifically labeled by both ligands in rabbit and guinea pig preparations provided that the skeletal muscle membranes used for purification were derived from fresh and not previously frozen and thawed tissue. The photoaffinity labeled polypeptide (termed here alpha 1) is different from the previously described alpha subunit in that it has the identical electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gels irrespective of pretreatment either with N-ethylmaleimide or with dithiothreitol. The use of transverse tubular membranes isolated from previously frozen and thawed skeletal muscle results in a purified calcium channel preparation devoid of the alpha 1 subunit. In these preparations proteolytic degradation products of alpha 1 are labeled with both (-)-[3H]azidopine and [N-methyl-3H]LU 49888. Another large molecular weight polypeptide (termed here alpha 2) was also present in every purified calcium channel preparation studied. alpha 2 is distinct from alpha 1 in that reduction with dithiothreitol changes its apparent mass from 160-190 to 130-150 kDa. The alpha 2 subunit is not photoaffinity labeled either with (-)-[3H]azidopine or [N-methyl-3H]LU 49888. These data suggest that two distinct high molecular weight polypeptides (termed alpha 1 and alpha 2) are putative subunits of skeletal muscle calcium channels. Only the alpha 1 subunit contains both 1,4-dihydropyridine and phenylalkylamine receptors. alpha 2 is the same as the previously described alpha subunit (Curtis, B. M., and Catterall, W. A. (1984) Biochemistry 23, 2113-2118), but is neither a 1,4-dihydropyridine- nor a phenylalkylamine-binding protein.

Paradoxical augmentation of (-)Bay K 8644-induced calcium influx by nitrendipine

(-)Bay K 8644 produced a concentration-dependent contraction of porcine coronary artery rings with the maximal contraction at 10(-6) M. Pretreatment of the rings with 10(-6) M nitrendipine inhibited (-)Bay K 8644-induced contraction, while pretreatment with 10(-8) M nitrendipine potentiated the contraction elicited by (-)Bay K 8644. (-)Bay K 8644 (10(-6) M) significantly stimulated Ca2+ influx. Although 10(-8) M nitrendipine never stimulated Ca2+ influx, Ca2+ influx induced by (-)Bay K 8644 was significantly potentiated by pretreatment with 10(-8) M nitrendipine. Pretreatment with 10(-6) M nitrendipine significantly decreased Ca2+ influx in tissues treated with (-)Bay K 8644. Our results suggest that the increased Ca2+ influx might be involved in the mechanisms by which (-)Bay K 8644-induced contraction was potentiated by pretreatment with nitrendipine.

Absorbable polydioxanone suture for venous anastomoses: experimental studies using venography and transluminal angioscopy

Because of their increased tendency to stenosis and spasm and thrombosis, results after venous anastomoses are often unsatisfactory. Nonabsorbable sutures and a continuous suture technique have been suggested to have a negative effect on the compliance of vascular anastomoses. Eighty venous anastomoses were performed with either an interrupted or continuous suture technique, using polypropylene or polydioxanone (PDS) sutures, according to a randomised experimental model. The anastomoses were divided in four groups: (1) Nonabsorbable suture material, continuous suture technique; (2) Nonabsorbable suture material, interrupted suture technique; (3) Absorbable suture material, continuous suture technique; and (4) Absorbable suture material, interrupted suture technique. The morphology of the anastomoses was controlled by venography directly after closure of the wound and at weekly intervals for 2 months and monthly intervals thereafter until 2 years had passed. In 10 cases venography was followed by transluminal angioscopy in the early postoperative period and after 1, 2, 4, 8 and 12 weeks. In the first 2 months moderate and high degree stenoses were found in all 4 groups by venography. After 8 weeks there was a significant decrease in the incidence of stenosis in all groups with the exception of the group, in which continuous nonabsorbable suture had been used. Using angioscopy a marked swelling of the intima at the site of the anastomoses could be detected in the early postoperative period in all experimental groups. After 2 months no significant narrowing could be identified in groups 2, 3 and 4.(ABSTRACT TRUNCATED AT 250 WORDS)