Effect of ultra-high pressure homogenization on the interaction between bovine casein micelles and ritonavir

PURPOSE

The aim of this work was to develop a milk-based powder formulation appropriate for pediatric delivery of ritonavir (RIT).

METHODS

Ultra-high pressure homogenization (UHPH) at 0.1, 300 and 500 MPa was used to process a dispersion of pasteurized skim milk (SM) and ritonavir. Loading efficiency was determined by RP-HPLC-UV; characterization of RIT:SM systems was carried out by apparent average hydrodynamic diameter and rheological measurements as well as different analytical techniques including Trp fluorescence, UV spectroscopy, DSC, FTIR and SEM; and delivery capacity of casein micelles was determined by in vitro experiments promoting ritonavir release.

RESULTS

Ritonavir interacted efficiently with milk proteins, especially, casein micelles, regardless of the processing pressure; however, results suggest that, at 0.1 MPa, ritonavir interacts with caseins at the micellar surface, whilst, at 300 and 500 MPa, ritonavir is integrated to the protein matrix during UHPH treatment. Likewise, in vitro experiments showed that ritonavir release from micellar casein systems is pH dependent; with a high retention of ritonavir during simulated gastric digestion and a rapid delivery under conditions simulating the small intestine environment.

CONCLUSIONS

Skim milk powder, especially, casein micelles are potentially suitable and efficient carrier systems to develop novel milk-based and low-ethanol powder formulations of ritonavir appropriate for pediatric applications.

Determination of biological toxins using capillary electrokinetic chromatography with multiphoton-excited fluorescence

We report a highly sensitive and rapid strategy for characterizing biological toxins based on capillary electrokinetic chromatography with multiphoton-excited fluorescence. In this approach, aflatoxins B1, B2, and G1 and the cholera toxin A-subunit are fractionated in approximately 80 s in a narrow-bore electrophoretic channel using the negatively charged pseudostationary phase, carboxymethyl-beta-cyclodextrin. The aflatoxins--highly mutagenic multiple-ringed heterocycles produced by Aspergillus fungi--are excited at the capillary outlet through the simultaneous absorption of two to three 750-nm photons to yield characteristic blue fluorescence; cholera toxin A-subunit, the catalytic domain of the bacterial protein toxin from Vibrio cholera, is excited through an unidentified multiphoton pathway that apparently includes photochemical transformation of an aromatic residue in the polypeptide. The anionic carboxymethyl-beta-cyclodextrin, used to chromatographically resolve the uncharged aflatoxins, enhances emission from these compounds without contributing substantially to the background. Detection limits for these toxins separated in 2.1-micron-i.d. capillaries range from 4.4 zmol (approximately 2700 molecules) for aflatoxin B2 to 3.4 amol for the cholera toxin A-subunit. Larger (16-micron-i.d.) separation capillaries provide concentration detection limits for aflatoxins in the 0.2-0.4 nM range, severalfold lower than achieved in 2.1-micron capillaries. These results represent an improvement of > 10(4) in mass detectability compared to previously published capillary separations of aflatoxins and demonstrate new possibilities for the analysis of proteins and peptides.

Overcoming exercise barriers in older adults

Barriers to exercise among older adults include personal factors such as discomfort, fear of injury, and social isolation, plus environmental difficulties such as lack of access and unfavorable weather. When selecting tactics to overcome the barriers, it is helpful to consider the patient's position within the six stages of behavior change. Key measures include controlling pain, treating chronic conditions, explaining the benefits of exercise, dispelling misconceptions, identifying personal goals that exercise can help the patient attain, setting realistic exercise goals, and following up.

Aberrant nodulation response of Vigna umbellata to a Bradyrhizobium japonicum NodZ mutant and nodulation signals

The (Brady)rhizobium nodulation gene products synthesize lipo-chitin oligosaccharide (LCO) signal molecules that induce nodule primordia on legume roots. In spot inoculation assays with roots of Vigna umbellata, Bradyrhizobium elkanii LCO and chemically synthesized LCO induced aberrant nodule structures, similar to the activity of these LCOs on Glycine soja (soybean). LCOs containing a pentameric chitin backbone and a reducing-end 2-O-methyl fucosyl moiety were active on V. umbellata. In contrast, the synthetic LCO-IV(C16:0), which has previously been shown to be active on G. soja, was inactive on V. umbellata. A B. japonicum NodZ mutant, which produces LCO without 2-O-methyl fucose at the reducing end, was able to induce nodule structures on both plants. Surprisingly, the individual, purified, LCO molecules produced by this mutant were incapable of inducing nodule formation on V. umbellata roots. However, when applied in combination, the LCOs produced by the NodZ mutant acted cooperatively to produce nodulelike structures on V. umbellata roots.

Endothelin-stimulated Ca2+ mobilization by 3T3-L1 adipocytes is suppressed by tumor necrosis factor-alpha

The cytokine tumor necrosis factor-alpha (TNFalpha) contributes to metabolic changes in disease states such as insulin resistance. However, the mechanism by which TNFalpha alters cellular function in these conditions is poorly understood. Because changes in intracellular calcium concentration plays a critical role in hormone action we investigated the effect of TNFalpha on calcium homeostasis in 3T3-L1 adipocytes. In these studies we show that TNFalpha causes a concentration- and time-dependent decrease in Na+/myo-inositol cotransporter (SMIT) mRNA levels and myo-inositol accumulation as well as a decrease in myo-inositol incorporation into phosphoinositides. These changes coincided with a decrease in endothelin-1-induced phosphatidylinositol (PI) cycle activity in 3T3-L1 adipocytes chronically exposed to TNFalpha. Endothelin-1-induced mobilization of calcium from intracellular stores was also diminished by TNFalpha. The effect of TNFalpha on endothelin-1-induced PI cycle activity and calcium mobilization was not due to a decrease in endothelin receptors. However, TNFalpha did cause a moderate decrease in phosphatidylinositol 4,5-bisphosphate (PIP2)-specific phospholipase C (PLC) activity in 3T3-L1 adipocytes. Combined, a decrease in phosphoinositide production and PIP2-specific PLC activity could be responsible for altering PI cycle activity and the generation of the second messenger myo-inositol 1,4,5-trisphosphate, thereby reducing calcium mobilization. Such changes in intracellular signaling may contribute to the pathophysiology of insulin resistance associated with TNFalpha.

Accidental radiation injury to the hand: anatomical and physiological considerations

A case study describing an accident in Mexico caused by failure to de-energize an x-ray spectrometer prior to repair is presented. The evolution, medical management, and outcome of the radiation injury to the hand are briefly reviewed. A discussion follows, with radiation injury and thermal burns compared and contrasted. The anatomy and physiology of thick skin and the vascular system of the hand are reviewed so that the reader will have a better understanding of the role of vascular injury in the pathological process that leads to tissue atrophy and radiation necrosis. Hyperbaric oxygen therapy, sympathectomy, and other techniques for improving circulation in involved areas are reviewed.

Nodule development induced by mutants of Bradyrhizobium japonicum defective in cyclic B-glucan synthesis

The soybean response to inoculation with B. japonicum mutants defective in cyclic beta-(1-->3), beta-(1-->6) glucan synthesis was examined by electron microscopy and by monitoring the expression of early and late nodulin genes. Two mutants were examined. Strain AB-14 is an ndvB mutant and is unable to synthesize beta-glucans. Strain AB-1 is an ndvC mutant and produces cyclic glucans containing 95 to 100% beta-(1-->3) glycosidic linkages. Nodules formed by either mutant were defective in nitrogen fixation activity. Soybean plants inoculated with strain AB-14 formed nodules roughly at the same rate as the wild-type strain USDA110, but nodulation by strain AB-1 was significantly delayed. Microscopy of nodules formed by strain AB-14 showed an overall ultrastructure similar to nodules formed by the wild type. However, in some nodules bacteroids were limited to only one part of the infected cells and in others the few bacteroids present showed signs of degradation. Nodulelike structures were formed by strain AB-1 that showed some signs of cellular differentiation. For example, clear parenchyma and sclerenchyma tissue could be seen. However, no infection threads or bacteria were evident in these structures. The expression of early (e.g., ENOD2 and ENOD55) and late (e.g., NOD26 and leghemoglobin) nodulins was examined. Nodules formed by strain AB-14 expressed all of the nodulins tested but at a reduced level. Expression of late nodulins was delayed in strain AB-14-induced nodules. Nodules formed by strain AB-1 were more strongly affected in nodulin expression. Although leghemoglobin synthesis was not detected, infection-specific nodulin transcripts of GmN93 and ENOD55 were detected. However, expression of the early nodulins ENOD2 and ENOD55 was considerably delayed and only apparent when assayed 21 days postinoculation. A low level of expression of intermediate nodulin GmN70 and late nodulin NOD26 could also be detected by 21 days postinoculation. The microscopy data show that tissue differentiation occurs in these nodules even in the absence of active bacterial invasion. These results demonstrate the importance of cyclic beta-(1-->3), beta-(1-->6) glucan synthesis to symbiotic development in soybean.

Phenotypic characterization and regulation of the nolA gene of Bradyrhizobium japonicum

Two Bradyrhizobium japonicum nolA mutants were constructed and used to test the functional role of NolA in nodulation. Contrary to the previous hypothesis that NolA acts as a repressor of nod gene transcription, the expression of a nodD1-lacZ or nodY-lacZ fusion in the nolA mutant strains was similar to that found in the wild type. However, NolA does appear to act as a transcriptional regulatory protein since it is required for its own expression, as well as that of nodD2. Expression of NodD2 from a constitutive promoter led to a significant reduction in nodC-lacZ activity. Therefore, the repression of nod gene expression by NolA is likely an indirect effect, perhaps mediated by other genes (e.g., nodD2) that are regulated by NolA. When inoculated onto soybean roots, the nolA mutant strains showed only a slight delay in nodulation as compared to the wild type. However, the mutant strains were grossly defective in nodulation and nitrogen fixation on cowpea plants. Microscopic examination of soybean nodules induced by the nolA mutant strains showed developmental and morphological characteristics similar to nodules formed by the wild type with only a slight delay in bacteroid maturation. In contrast, cowpea nodules induced by the nolA mutant strains contained fewer infected cells and bacteroids were not found in a typical symbiosome structure. These results indicate that NolA is a transcriptional activator required for the expression of genes that play a role not only in the early stages of infection, but also during the later stages of bacteroid development and maintenance.

Identification of the tailspike protein from the Salmonella newington phage epsilon 34 and partial characterization of its phage-associated properties

The lipopolysaccharide (LPS) of the Salmonella cell surface serves as the receptor for a very large number of bacterial viruses. The tailspike protein from these viruses recognizes the LPS as its initial receptor. It is proposed that the study of the P22 and epsilon 34 tailspike proteins could serve as a model for the study of the interaction of proteins with LPS. Toward this end, the tailspike protein of the epsilon 34 phage has been identified. The data suggest similarities between the epsilon 34 tailspike protein and the P22 tailspike protein. Some properties related to the interaction of the phage tailspike with its receptor are reported.

Necrotizing fasciitis and septic shock caused by Vibrio cholerae acquired in San Diego, California

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Heterotopic ossification following uncemented total hip arthroplasty. Effect of the operative approach

A consecutive series of 112 primary uncemented total hip arthroplasties using the same type of prosthesis was reviewed for the incidence and severity of heterotopic ossification (HO). Sixty-three of these patients underwent a posterior approach (group 1) and 49 underwent an anterolateral approach (group 2). The two groups were virtually identical when risk factors, such as age, sex, estimated blood loss, length of surgery, and diagnosis were compared. Patients in group 1 had a significantly lower incidence and severity of HO than those in group 2. The overall incidence of class III or IV HO was very low (8%), indicating that uncemented total hip arthroplasty in itself is not predisposed to moderate or severe degrees of HO. Patients undergoing uncemented total hip arthroplasty through an anterolateral approach had a higher incidence of HO than those undergoing a posterior approach in this series.

Effect of various methods of restoring flexor sheath integrity on the formation of adhesions after tendon injury

The effect of three different methods of restoring flexor sheath integrity on the formation of adhesions around traumatized flexor tendons was studied by use of a chicken animal model. The three methods were: I, Primary sheath repair; II, a fascia patch; and III, a synthetic polytetrafluoroethylene surgical membrane patch. These were compared with controls in which the flexor sheath was excised. Adhesion formation was assessed both biomechanically by measuring the parameter work of flexion, (which represents the resistance to tendon gliding caused by adhesions), and also histologically. At 3 and 6 weeks there was no significant difference in the work of flexion between either the sheath repair or fascia patch digits, and the sheath excised controls. However, use of the synthetic polytetrafluorethylene patch did result in tendon gliding, which was significantly better than the controls. In contrast, at 12 weeks all three methods of sheath reconstruction had similar tendon gliding biomechanics, and all were significantly better than the controls. Histologically, at 3 weeks, the biologic barriers sheath repair and fascia patch were associated with a layer of granulation tissue, which adhered to the underlying tendon. This was similar to the appearance of the sheath excised control digits. The synthetic patch was not associated with a significant inflammatory reaction at this time period and was clearly separated from the tendon. However, by 6 and 12 weeks the granulation tissue in all three sheath reconstruction groups had undergone remodeling to a greater degree than had the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical and histologic evaluations of pulley reconstructions in nonhuman primates

A2 pulleys were reconstructed in nonhuman primates using expanded polytetrafluoroethylene, woven nylon, and fascia. Biomechanical and histologic evaluations were done after death at 18 weeks. Tendons were normal after all pulley reconstructions. Polytetrafluorethylene had a greater breaking strength than woven nylon or fascia, or control pulleys, both at 18 weeks and before implantation. Histologic analyses revealed fibrous ingrowth of host tissues, no adhesions, no trauma to underlying flexor tendons, and the absence of an inflammatory response, for all pulley types.

A nonparallel, nonisometric synthetic graft augmentation of a patellar tendon anterior cruciate ligament reconstruction. A model for assessment of stress shielding

The potential for a rigidly fixed synthetic graft placed in the over-the-top position to be stress shielding/stress sharing with the patellar tendon autograft was assessed in a primate model. A patellar tendon autograft was placed anatomically and tensioned at 2 pounds for all of the groups. In the augmented animals, a 30 strand braided graft 10 cm in length of expanded polytetrafluoroethylene was tightened with the knee in full extension. After 6 months of unrestricted cage activity the animals were sacrificed and biomechanical testing performed. The augmented patellar tendon autografts demonstrated less laxity in extension as compared to the autografts alone. A minimal decrease in the load and stiffness to failure for the augmented groups as compared to the nonaugmented knees was noted. However, both the reconstruction groups had a significant decrease in the load to failure at 6 months (50% of the normal ACL). In summary, this study demonstrated that a synthetic graft augmentation can be performed in the over-the-top position and minimize knee laxity, especially during terminal extension. With this technique, the laxity was minimized while the incorporation and strengthening of the biologic autograft occurred at a rate similar to the unaugmented reconstruction.

Perfusion of the abductor digiti quinti after transfer on a neurovascular pedicle

The perfusion to the abductor digiti quinti muscle was measured, both before and after, opponensplasty transfer on its neurovascular pedicle in six monkeys, with use of the hydrogen wash-out technique to determine blood flow. The musculotendinous unit can be transferred without vascular compromise, but detachment of the abductor digiti quinti from its origin on the pisiform results in ischemia. Such impairment of blood flow to the muscle may be responsible for the postoperative fibrosis, which has been seen as a complication of the procedure.

Quantification of the perfusion of the anterior cruciate ligament and the effects of stress and injury to supporting structures

The perfusion of the normal ACL was quantitated using the hydrogen washout technique in a canine model. This was compared to the perfusion of the synovium in the suprapatellar pouch. Changes in the ACL perfusion were quantitated after the application of anterior stress, division of the infrapatellar fat pad, and dissection of the synovium enveloping the ACL. The ACL is relatively hypovascular, with one-half the blood flow of the synovium of the suprapatellar pouch. Application of an anterior stress diminishes the blood flow to the ACL to one-fifth of the baseline value, an effect which is reversible. Division of the infrapatellar fat pad causes a two-fold decrease in perfusion to the ACL, whereas dissection of the enveloping synovium results in a complete cessation of blood flow.

Effect of fatty acid composition on insulin and IGF-I binding in retinoblastoma cells

Receptors for insulin and other hormones are often influenced by their environment, including fatty acid content and membrane fluidity. Y79 retinoblastoma cells enriched with arachidonic or docosahexaenoic acid show an increase in membrane fluidity determined by fluorescence polarization using the plasma membrane-specific probe, trimethylammonium-diphenylhexatriene. Unlike cells enriched with polyunsaturated fatty acids, cells cultured in media containing palmitic or oleic acid showed no changes in membrane fluidity or fatty acid composition. Cells enriched with docosahexaenoic acid show an increase in insulin binding at 15 degrees C that is due to an increase in the number of available insulin receptor sites on the plasma membrane. In contrast, insulin binding is not altered in cells enriched with arachidonic, palmitic or oleic acid. Furthermore, the binding of insulin-like growth factor-I (IGF-I) in Y79 cells is not changed by the fatty acid unsaturation of the cell membrane. Because docosahexaenoic acid is naturally present in high concentrations in the retina these studies suggest it may have a role in modulating insulin binding and function.

Flexor tendon pulley reconstructions--a histological and ultrastructural study in non-human primates

The feasibility of A2 pulley reconstructions using expanded polytetrafluoroethylene (PTFE), woven nylon, and fascia lata was assessed in a non-human primate model and evaluated by light and scanning electron microscopy 18 weeks after implantation. No adhesions were found between reconstructed pulleys and flexor tendons. All types of pulley were intact and incorporated by host tissues, without evidence of a foreign body reaction. The inner surfaces of the fascial and PTFE pulleys, apposed to the gliding flexor tendons, were smooth and covered by a fibrous layer of tissue on microscopic and ultrastructural examination. The apposed visceral synovial surfaces of the F.D.P. tendon were indistinguishable from those from unoperated digits. The FDP tenosynovium apposed to woven nylon pulleys was more fibrillar and granular. Based on the results of the present study and on previous biomechanical data, expanded PTFE should be considered as a material for pulley reconstruction; it is incorporated by host tissues, elicits no foreign body reaction and causes no adhesions or traumatic changes to underlying flexor tendons. It is not yet known whether it has sufficient breaking strength to meet the functional demands of human pulleys.

Flexor Tendon Pulley Reconstructions—A Histological and Ultrastructural Study in Non-Human Primates

The feasibility of A2 pulley reconstructions using expanded polytetrafluoroethylene (PTFE), woven nylon, and fascia lata was assessed in a non-human primate model and evaluated by light and scanning electron microscopy 18 weeks after implantation. No adhesions were found between reconstructed pulleys and flexor tendons. All types of pulley were intact and incorporated by host tissues, without evidence of a foreign body reaction. The inner surfaces of the fascial and PTFE pulleys, apposed to the gliding flexor tendons, were smooth and covered by a fibrous layer of tissue on microscopic and ultrastructural examination. The apposed visceral synovial surfaces of the F.D.P. tendon were indistinguishable from those from unoperated digits. The FDP tenosynovium apposed to woven nylon pulleys was more fibrillar and granular. Based on the results of the present study and on previous biomechanical data, expanded PTFE should be considered as a material for pulley reconstruction; it is incorporated by host tissues, elicits no foreign body reaction and causes no adhesions or traumatic changes to underlying flexor tendons. It is not yet known whether it has sufficient breaking strength to meet the functional demands of human pulleys.

Pathomechanics of posterior sag of the tibia in posterior cruciate deficient knees. An experimental study

This study was an investigation of the pathomechanics of posterior sag of the tibia in knees with posterior knee instability caused by PCL deficiency. By using fresh cadaver knees, the authors hoped to define the relationship of the posterior joint capsule and the medial and lateral collateral ligaments (MCL, LCL) with posterior knee instability in the PCL deficient knee. Thirty newtons of posterior stress were applied to the knees to simulate postoperative conditions. Roentgenographic methods were then used to evaluate posterior sag and change in the distance between the origin and insertion of the PCL. Strain gauges were used to measure the actual strain of the PCL and the collateral ligaments. The PCL, the posterior capsule, and the medial and lateral collateral ligaments were sequentially divided and the above measurements were then repeated in the same way, using 30 N of applied posterior stress. When only the PCL was cut, posterior sag and medial rotation of the tibia occurred with increasing severity as flexion increased. No sagging or rotation of the tibia was observed at full extension in the knees that had isolated PCL "injury". When the posterior capsule was sectioned, no significant changes were noted in the severity of the sag or the rotation. When the MCL or LCL was divided in a PCL deficient knee, greater sag occurred with flexion and a significant sag was observed even at full extension. The MCL "injury" was associated with increased medial rotation, whereas LCL "injuries" were associated with lateral rotation of the tibia.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitivity and specificity of somatosensory and neurogenic-motor evoked potentials in animals and humans

The purpose of this study was to report the effects of spinal cord compression, ischemia, and distraction on clinical status, and somatosensory (SEP) and neurogenic-motor evoked potentials (NMEPs) in animals. The authors also reported their clinical experience with NMEPs elicited from humans undergoing surgery for spinal deformities. Results from the animal studies indicate that NMEPs are more sensitive and specific to the effects from spinal cord compression, ischemia, and distraction than SEPs. In every situation, NMEPs always correlated with the animal's post-surgical clinical status, while SEPs demonstrated an unacceptable false positive and false negative rate. In the 111 clinical cases in which NMEPs were administered, reliable NMEPs were easily elicited in more than 90% of the cases. In the remaining cases, no reliable NMEPs could be recorded because of procedural errors, which have been resolved. The results from this study suggest that the use of NMEPs should be considered as an adjunct to SEPs when monitoring spinal cord function during surgery.

The effect of vascularization on avian flexor tendon repair. A biochemical study

Although it has been demonstrated in experimental animals that vascular perfusion functions less effectively than diffusion as a nutrient pathway to the uninjured flexor tendon, it is recognized that the nutritional requirements of an injured flexor tendon may be different. The present study examines several biochemical parameters of avian flexor tendon repair, during a six-week period, in the presence of an intact vinculum longum and with the vinculum longum ligated. Formation of collagen/noncollagen protein, glycosaminoglycan synthesis, and tissue levels of both DNA and hexosamine were quantified. The absence of the vincular blood supply did not affect the levels of total DNA and hexosamine, did not alter the pattern of either protein or glycosaminoglycan formation in the early healing phase, and did not impair the overall synthesis of collagen and noncollagen protein throughout the six-week study period. However, the pattern of collagen and noncollagen protein synthesis differed in lacerated tendons during the period of repair; noncollagen protein synthesis peaked at ten days, while collagen synthesis increased uniformly throughout the 42-day period of study. There was a notable decrease in total matrix hydroxyproline (collagen) during repair, which continued throughout the entire first three weeks after laceration. Thus, the actual percentage of collagen synthesis decreased during the first three weeks of repair and began to return to its normal uninjured level by the sixth week.(ABSTRACT TRUNCATED AT 250 WORDS)

Osteoporotic correlates of alcoholism in young males

A group of 22 white males (ages, 28 to 40 years) with histories of chronic alcohol abuse ranging from 1 to 21 years were evaluated for trabecular bone mineral density in the left femoral neck area. A group of age and weight-matched white males with no history of alcoholism served as controls. All participants completed medical history questionnaires regarding fracture history, dietary habits, medications, and physical activity. Singh femoral trabecular indices also were measured for the alcoholic participants. Analysis of bone mineral data as measured by dual photon absorptiometry revealed no statistically significant reduction in the bone mineral densities of the alcoholic group when compared to the controls. No differences were seen in the areas of the femoral neck, Ward's triangle, and greater trochanter. Duration of alcoholism also was not correlated with the degree of osteopenia. Singh index measurements of right and left femoral heads were compared and revealed no significant differences within individual patients. Left femoral Singh index values averaged 5.5 (range, 4 to 6) for the alcoholic group and were not indicative of decreased bone mineral density. It is concluded from this study that chronic alcoholism associated with heavy smoking most likely has a debilitating effect on the trabecular bone density of white males, yet clinical and radiographic evidence is not widely manifested in men under the age of 40 years.

Differences and similarities in muscarinic receptors of rat heart and retina: effects of agonists, guanine nucleotides, and N-ethylmaleimide

Muscarinic receptor stimulation inhibits cyclic AMP formation in rat atria but not in retina. We compared the properties of the muscarinic receptors in rat atrial and retinal membranes using the antagonist [3H]quinuclidinyl benzilate. In both atria and retina there is a single binding site for antagonists, while agonists appear to interact at two classes of binding sites. Muscarinic receptors in atria and retina have the same apparent affinities for several antagonists and for a series of muscarinic agonists. In both tissues N-ethylmaleimide decreases agonist affinity for the high-affinity binding sites. Muscarinic receptors in atria and retina differ, however, in several properties relating to the proportions of high- and low-affinity agonist sites. First, guanine nucleotides markedly increase the proportion of low-affinity binding sites in atria, but not in retina. Second, for all agonists there are fewer high-affinity binding sites in retina. Third, the "partial agonist" pilocarpine appears to interact with two classes of binding sites in atria, but with only a single class of sites in retina. Our data suggest that muscarinic receptors that inhibit cyclic AMP formation and those that do not share common properties that determine receptor affinity for agonists and classic antagonists. The differences between these receptors are manifest, however, in the effects of guanine nucleotides and the ability of agonists, especially those of low efficacy, to affect the proportion of high- and low-affinity sites and to effect a biological response.

Heterogeneity of binding sites on cardiac muscarinic receptors induced by the neuromuscular blocking agents gallamine and pancuronium

The binding of [3H]quinuclidinyl benzilate ([3H]QNB) to cardiac muscarinic receptors was inhibited not only by classical muscarinic antagonists but also by nicotinic blocking agents and inhibitors of acetylcholinesterase. Gallamine, pancuronium, ambenonium, and decamethonium were the most potent of these agents examined. All of the nicotinic antagonists with significant muscarinic receptor activity had two or three quaternary nitrogens, and the potency of a series of these compounds was a function of the distance between quaternary nitrogens. The effects of gallamine and pancuronium were studied in detail because these neuromuscular blocking agents showed heterogeneity in their binding to cardiac muscarinic receptors, whereas classical muscarinic antagonists such as QNB and atropine did not. Gallamine did not compete for all of the [3H]QNB binding sites on atrial membranes, but left at least 20% of [3H]QNB binding unaffected. Curves of pancuronium competition for [3H]QNB binding were shallow, consistent with two binding sites for pancuronium, with approximately 20% having low affinity. Additionally, in the presence of gallamine or pancuronium, [3H]QNB binding sites were no longer homogeneous, and Scatchard plots became nonlinear. Guanine nucleotides did not alter the effect of gallamine or pancuronium on [3H]QNB binding. Gallamine and pancuronium showed no agonist activity but, like atropine, completely antagonized muscarinic receptor-mediated inhibition of cyclic AMP formation. However, differences in the behavior of gallamine and atropine suggested that gallamine was not a purely competitive antagonist. Gallamine did not protect against receptor alkylation by propylbenzilylcholine mustard, and [3H]QNB dissociation was apparently slowed by gallamine. We interpret our data to suggest that gallamine not only competes for [3H]QNB binding sites, but also binds at a secondary site on the receptor, forming a ternary complex with [3H]QNB. Heterogeneity in ligand binding is proposed to result from the dual actions of gallamine and pancuronium as ligands at both primary and secondary sites on the cardiac muscarinic receptor.

Activation and blockade of cardiac muscarinic receptors by endogenous acetylcholine and cholinesterase inhibitors

Cholinesterase inhibitors are known to potentiate the effects of acetylcholine (ACh) and vagal stimulation on the myocardium. The studies presented here demonstrate that cholinesterase inhibitors (ChEI) also have activity in isolated atria in the absence of extrinsic cholinergic stimulation and that, depending on the ChEI, either indirect stimulation or direct blockade of cardiac muscarinic receptors can occur. Muscarinic agonists inhibit cyclic AMP formation in atria and the ChEIs physostigmine, neostigmine and echothiophate likewise produce a marked attenuation of isoproterenol-stimulated cyclic AMP accumulation The effect of physostigmine appears to result from muscarinic receptor activation by endogenous ACh as it is blocked by atropine. In contrast, the ChEI ambenonium does not stimulate but instead blocks muscarinic receptors coupled to cyclic AMP accumulation. Radioligand binding studies provide direct evidence that both ambenonium and demecarium are relatively potent muscarinic receptor antagonists, whereas physostigmine and other ChEI have little direct receptor activity. Physostigmine and ambenonium also have different effects on heart rate in vivo, the former potentiating and the latter apparently blocking vagal tone. The inhibition of cyclic AMP formation produced by physostigmine can be used as a measure of the concentration of endogenous ACh available at muscarinic receptor sites. Physostigmine blocks cyclic AMP formation in atria incubated in the absence of calcium or in the presence of tetrodotoxin, suggesting that endogenous ACh is spontaneously released in the absence of neuronal activity or depolarization-secretion coupling.

Verapamil competitively inhibits alpha 1-adrenergic and muscarinic but not beta-adrenergic receptors in rat myocardium

Recent studies indicate that antagonism of calcium channels may not be the only mechanism whereby drugs such as verapamil alter myocardial function. We have examined the effect of verapamil on the binding of [3H]prazosin (alpha 1-adrenergic), [3H]quinuclidinyl benzilate (QNB, muscarinic) and [3H]dihydroalprenolol (DHA, beta-adrenergic) to membranes prepared from rat heart. Verapamil competed for the binding of these radioligands in the following rank order: [3H]prazosin greater than [3H]QNB greater than [3H]DHA (Ki for verapamil = 0.6 microM, 7 microM, and 72 microM, respectively). Verapamil (10 microM) competitively inhibited [3H]prazosin binding to rat ventricular membranes; the apparent dissociation constant (KD) of [3H]prazosin increased from 0.13 +/- 0.02 to 1.5 +/- 0.6 nM (SD) without change in maximal binding capacity (Bmax). The effect of verapamil on the affinity of [3H]prazosin was completely reversed by washing the membranes. The verapamil derivative D-600 also inhibited [3H]prazosin binding (Ki = 1.1 microM). Verapamil (30 microM) competitively inhibited [3H]QNB binding in both atria and ventricles and increased the apparent KD of [3H]QNB fivefold (from 0.07 nM to 0.32 nM) without decreasing Bmax. Verapamil was a less potent inhibitor of [3H]DHA binding and its effect was noncompetitive: the KD for DHA was unaltered by 100 microM verapamil while the Bmax decreased severalfold. We conclude that verapamil, at concentrations clinically achieved in the myocardium (approximately 1 microM), competitively inhibits binding to alpha 1-adrenergic and muscarinic receptors and that this inhibition may play a role in the effects of verapamil on the heart.