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J A Halperin

Publications and source records attributed to J A Halperin.

At least 37 records · Page 2Linked to original sources
PubMed1991

Palytoxin induces an increase in the cation conductance of red cells.

Palytoxin (PTX), isolated from the marine soft coral Palythoa tuberculosa, increases the cation conductance of human red cell membranes. In the presence of 10(-10) M PTX and 10(-5) M DIDS, the membrane potential approximates the equilibrium potential for Na+ or K+ rather than Cl-. Even in the absence of DIDS, the Na+ and K+ conductances were greater than the Cl- conductance. The selectivity of the PTX-induced cation conductance is K+ greater than Rb+ greater than Cs+ greater than Na+ greater than Li+ much greater than choline+ greater than TEA+ much greater than Mg2+. Measurements of K+ efflux revealed two apparent sites for activation by PTX, one with a Kal of 0.05 nM and a maximum flux, nu max1, of 1.4 mol/liter of cells per h and another with a Ka2 of 98 nM and a nu max2 of 24 mol/liter of cells per h. These effects of PTX are completely blocked by external ouabain (300 microM) and prevented by internal vanadate (100 microM). When the PTX channels are open, the Na,K pumps do not catalyze ATP hydrolysis. Upon thorough washout of cells exposed to about five molecules of PTX/pump, the Na,K pump of these cells operates normally. Blockage of the positively charged NH2 terminus of PTX with a p-bromobenzoyl group reduces the potency of the compound to induce Na and K fluxes by at least a factor of 100, and to compete with the binding of [3H]ouabain by at least a factor of 10. These data are consistent with the conclusion that PTX binds reversibly to the Na,K pumps in the red cell membrane and opens a (10-pS) channel equally permeable to Na and K at or near each pump site.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Voltage-activated cation permeability in high-potassium but not low-potassium red blood cells.

We have recently reported that voltage-activated fluxes of Na, K, and Ca occur in human red blood cells [J.A. Halperin, C. Brugnara, M. Tosteson, T. Van Ha, and D. C. Tosteson. Am. J. Physiol. 257 (Cell Physiol. 26): C986-C996, 1989]. The cation permeability increases progressively as the membrane potential becomes more inside positive above +20 mV. In this paper we show that this effect also occurs in high-potassium (HK), but not in low-potassium (LK), sheep and dog red blood cells. This result suggests that the voltage-activated cation transport pathway is not the result of nonspecific dielectric breakdown of the lipid bilayer but, rather, relates to some membrane component, presumably a protein, that is expressed in HK human and sheep but not in LK sheep and dog red blood cells.

Animals↗
PubMed1989

Digitalis-like properties of an inhibitor of the Na+/K+ pump in human cerebrospinal fluid.

Work originally reported by my laboratory has established that a constituent of human cerebrospinal fluid (CSF) specifically inhibits the Na+/K+ pump in human red cells and the activity of the enzyme (Na+/K+)-ATPase. Furthermore, we have shown that the inhibitory compound has a molecular weight of approx. 600 and is sensitive to proteolytic digestion, indicating that it is a small peptide. I describe here that the inhibitor of the Na+/K+ pump in human CSF mimics the effects the digitalis glycosides in 3 different assay systems: the Na+/K+ pump in human red cell, the (Na+/K+)-ATPase activity of a purified enzyme and the specific binding of [3H]ouabain to its receptor in the red cell membrane. Moreover, the inhibitor in human CSF is a competitive inhibitor of the stimulation of the Na+/K+ pump by extracellular K+. Based on these findings, I propose that a small peptide with digitalis-like properties present in human CSF is an endogenous regulator of the Na+/K+ pump in cells of the central nervous system. This digitalis-like substance could be one factor regulating the K+ concentration of the CSF and controlling the secretion of CSF by the choroid plexus.

Adult↗
PubMed1989

Suppression of cerebrospinal fluid (CSF) production by a Na+/K+ pump inhibitor extracted from human cerebrospinal fluid.

A low molecular weight compound (about 600 daltons) extracted from human cerebrospinal fluid, and sensitive to proteolytic enzymes, has been shown to mimic the specific inhibitory effects of cardiac glycosides on the Na+/K+ pump of erythrocytes. The compound, which was labelled CSF-inhibitor (CSF-I) and reconstituted in artificial rabbit CSF, was used to study its effects on the rate of CSF formation in rabbits. Three groups of adult New Zealand white rabbits of either sex, anesthetized with ketamine and xylazine, and artificially respired were subjected to ventriculocisternal perfusions. Baseline rates of CSF formation were obtained during the first 2 hours of perfusion when plain rabbit CSF was used as the perfusate. Thereafter, the animals were perfused for an additional 2 to 3 hours with either plain rabbits CSF (controls), rabbit CSF containing 10(-6) M ouabain (group 2) or CSF-I (group 3). The rate of CSF formation in control animals was observed to gradually decline with time (about 7.5% in 4 hours). The addition of ouabain to the perfusate caused an abrupt and marked 43% decline in the rate of formation while the addition of CSF-I resulted in a 57% decline. These results suggest that the peptide CSF-I which is present in human CSF may act as an endogenous regulator of CSF production.

Animals↗
PubMed1989

Voltage-activated cation transport in human erythrocytes.

We report here the effects of membrane potential on the permeability of the human erythrocyte to Na, K, and Ca. Membrane potential was changed either by varying the K concentration gradient in the presence of valinomycin or by varying the concentration gradient of the permeant anion nitrate in the presence of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. When the membrane potential was changed from inside negative (-10 mV) to inside positive (greater than 40 mV), influx, efflux, and net flux of Na and K increased. Marked net cation loss and cell shrinkage occurred in the absence of a chemical gradient for Na and K. This voltage-dependent increase in Na and K conductance is partially inhibited by 10 microM ruthenium red and persists when the membrane potential is returned to -10 mV after transient exposure to inside-positive potentials. A similar voltage-dependent behavior was found for Ca influx. The voltage-activated Ca influx is almost completely inhibited by 10 microM ruthenium red.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1989

Paroxysmal nocturnal hemoglobinuria. A complement-mediated disease.

Paroxysmal nocturnal hemoglobinuria (PNH) is a hemolytic disease characterized by an increased sensitivity of erythrocytes to the hemolytic action of complement. Two membrane proteins, the decay-accelerating factor and the C8-binding protein, which protect normal erythrocytes from the hemolytic action of complement, are deficient on the abnormal blood cells from patients with PNH. Other membrane proteins unrelated to complement regulation, but which share with the decay-accelerating factor and the C8-binding protein a common post-translational modification, namely a glycan-phosphatidylinositol linkage to the cell membrane, are also missing from PNH cells. In the present review, clinical, biological, and molecular aspects of PNH are discussed. In addition, diagnostic tests in clinical use are discussed, and new tests using indirect immunofluorescent assays are proposed.

Complement System Proteins↗
PubMed1989

Ca2+-activated K+ efflux limits complement-mediated lysis of human erythrocytes.

The lytic effect of complement on human erythrocytes has been reported by others to increase when Na+ is substituted for K+ in the external medium. In this paper we have investigated the hypothesis that net loss of K+ through a K+ transport pathway protects erythrocytes from complement-induced colloidosmotic swelling and lysis. Antibody-sensitized human erythrocytes containing different intracellular cation concentrations (nystatin treatment) were exposed to low concentrations of guinea pig serum in media of different cation composition; complement lysis was assessed by the release of hemoglobin and the volume of the surviving cells estimated by their density distribution profiles. Complement-dependent swelling and lysis of erythrocytes (a) were limited by the presence of an outwardly directed K+ electrochemical gradient and (b) were enhanced by carbocyanine, a specific inhibitor of the Ca2+-activated K+ transport pathway, and by absence of Ca2+ in the external medium. We propose that during complement activation a rising cytosolic calcium triggers the Ca2+-activated K+ permeability pathway, the Gardos effect, produces a net K+, Cl- and water loss, and thus limits the colloidosmotic swelling and lysis of erythrocytes.

Animals↗
PubMed1989

Potassium iodide as a thyroid blocker--Three Mile Island to today.

The Three Mile Island (TMI) nuclear emergency in the U.S. in March 1979 marked the first occasion when use of potassium iodide (KI) was considered for thyroid blocking of the population in the vicinity of a potentially serious release of fission products from a nuclear power reactor. In face of a demand that could not be satisfied by commercial supplies of low-dose KI drug products from the U.S. pharmaceutical industry, the Food and Drug Administration directed the manufacture and stockpiling of sufficient quantities of saturated solution of potassium iodide (SSKI) to provide protection for one million people in the event of a large-scale release of radioiodines. Although the drug was not used, the experience of producing, stockpiling, and making ready for use a large quantity of the drug resulted in significant public policy, regulatory, and logistical issues. A number of these issues have been resolved through scientific debate and consensus, development of official guidance regarding the proper role of KI in nuclear emergencies, and the approval of New Drug Applications for KI products specifically intended for thyroid blocking in nuclear emergencies. Other issues regarding broad-scale implementation of the guidelines remain today. This paper traces the history of the development and implementation of the use of KI from pre-TMI to the present.

Accidents, Occupational↗
PubMed1988

Characteristics of an inhibitor of the Na+/K+ pump in human cerebrospinal fluid.

Human cerebrospinal fluid (CSF) inhibits the Na+/K+ pump in human red cells and the activity of purified Na+/K+-ATPase (Halperin, J. A., Shaeffer, R., Galvez, L., and Malavé, S. (1985) Proc. Natl. Acad. Sci. U.S. A. 80, 6102-6104, 1983; Halperin, J. A., Martin, A. M., and Malavé, S. (1985) Life Sci. 37, 561-566. We describe here some properties of the CSF inhibitor of the Na+/K+ pump. Active material was extracted from human CSF with 50% methanol and then concentrated and desalted by ultrafiltration. This extract inhibited, in a dose-dependent manner, the ouabain-sensitive influx of K+ into human red cells and the activity of purified Na+/K+-ATPase. Partial separation of the inhibitory activity was achieved by gel filtration and reverse-phase high performance liquid chromatography. Inhibition of both pump and enzyme was specific in that other red cell membrane transport systems or enzymes examined were not influenced by CSF extracts. Dialysis and ultrafiltration experiments indicate that the molecular weight of the inhibitor is approximately equal to 600. The inhibitory activity is sensitive to proteolytic enzymes indicating that the inhibitor might be a small peptide. In the presence of CSF extract the K0.5 for external K+ to stimulate the Na+/K+ pump increased from 1.4 to 3.1 mM, suggesting that the CSF inhibitor competes with external K+ for stimulation of the pump. We estimate that the concentration of the inhibitor in CSF might be approximately equal to 50 pg/ml, a value close to the concentration of other active peptides found in human CSF.

Cerebrospinal Fluid Proteins↗
PubMed1988

Complement induces a transient increase in membrane permeability in unlysed erythrocytes.

The effects of low concentrations of human serum on antibody-sensitized sheep erythrocytes (EA) were studied. We report that exposure to low concentrations of serum induced a large but transient increase in the membrane permeability of those EA that do not lyse. This change in the permeability of the erythrocyte membrane resulted in net uptake of Na+ and decrease in cell K+, without affecting the total internal cation content. Although exposure to serum also allowed for net uptake of larger molecules like L-glucose, it did not lead to cell swelling. Experiments with sera genetically deficient in one of the terminal complement components showed that C8, but not C9, was required to produce the observed change in membrane permeability. Therefore, we propose that the C5b-8 complex can mediate the transient increase in permeability observed in unlysed erythrocytes during complement activation by whole serum.

Animals↗
PubMed1987

Effect of heparin-binding growth factors on monovalent cation transport in Balb/C 3T3 cells.

The changes in monovalent cation fluxes induced by class 1 and class 2 heparin-binding growth factors purified from bovine brain were studied in confluent quiescent Balb/C 3T3 cells. Both classes of HBGF's rapidly stimulate the activity of the Na+-K+ pump in a concentration-dependent manner that parallels their mitogenic activity. This effect requires the presence of external Na+ and is abolished by 1 mM amiloride. As with other growth factors, HBGF's increase the activity of the Na+-K+ pump by increasing Na+ influx into the cells via the amiloride-sensitive Na+-H+ exchange. These results indicate that rapid activation of cation transport is an early cellular response that follows binding of HBGF's to specific receptors on the surface of target cells.

Animals↗
PubMed1987

Properties of the Na+-K+ pump in human red cells with increased number of pump sites.

We studied the Na+/K+ pump in red cells from an obese human subject (MAJ) in which the number of pumps/cell was 10-20 times higher than normal. Through measurements of the kinetic properties of several modes of operation of the Na+/K+ pump we determined that the pumps in MAJ cells are kinetically normal. In the presence of adequate metabolic substrate the maximum rates of Na+ pumping and lactate production saturated at 60 and 12 nmol/1 cell per h, respectively. Under physiological conditions pump and "leak" Na+ fluxes were similar in MAJ and normal cells. Since internal Na+ was lower in MAJ than in normal cells (Nai+ approximately 2 and 8 mmol/1 cell, respectively), we conclude that the reduction in cell Na+ allows the Na+/K+ pump in MAJ cells to operate at lower fraction of maximum capacity and to compensate for the increased number of pumps.

Adenosine Triphosphate↗
PubMed1985

Increased digitalis-like activity in human cerebrospinal fluid after expansion of the extracellular fluid volume.

The present study was designed to determine whether acute expansion of the extracellular fluid volume influenced the digitalis-like activity of human cerebrospinal fluid (CSF), previously described by our laboratory. Human CSF samples, drawn before and 30 minutes after the intravenous infusion of 1 liter of either saline or glucose solutions, were assayed for digitalis-like activity by inhibition of either the 86Rb+ uptake into human erythrocytes or by the activity of a purified Na+ - K+ ATPase. The CSF inhibitory activity on both systems significantly increased after the infusion of sodium solutions but did not change after the infusion of glucose. These results indicate that the digitalis-like factor of human CSF might be involved in the regulation of the extracellular fluid volume and electrolyte content and thereby in some of the physiological responses to sodium loading.

Calcium↗
PubMed1983

Product selection, bioequivalence, and therapeutic equivalence: the generic drug market.

Pharmacists are continually faced with drug product selection decisions. When is a generic drug product equivalent to the innovator product and, thus, a suitable candidate for generic substitution? The FDA policy has been that only drug products that are therapeutic equivalents are candidates for product selection decisions. This paper outlines the regulatory and scientific framework for the FDA's policies and requirements for generic drug products. The history and current status of the Drug Efficacy Study Implementation (DESI) project is described. Originally begun in 1966 as a review of about 3,400 drug products, the review in mid-1983 is more than 90% complete, but its impact has already affected more than 7,000 marketed drug products. The therapeutic equivalence policy and the manner in which decisions on therapeutic equivalence are communicated are reviewed. Regulatory policies for the approval of generic drug products are reviewed and specific litigation challenging the rights of generic drug manufacturers to produce generic "look-alikes" and challenging the FDA's policy that a generic drug product is a new drug requiring an approved New Drug Application for marketing is discussed. The conclusion reached is that the evaluation of regulatory requirements and science is leading to a point where all generic drug products will be known to be safe, effective and therapeutically equivalent, and pharmacists can be optimistic about the quality of products in the generic drug market.

Legislation, Pharmacy↗