The mentored clinical casebook project at Harvard Medical School.

An excellent physician must be aware of the countless issues that affect each patient's health. Many medical education programs expose students to a broad spectrum of disparate knowledge and hope they will integrate all the pieces into a coherent whole. The authors describe an explicit approach to integration used at Harvard Medical School since 2003 that aims to enhance students' learning in medical school and throughout their medical careers: the Mentored Clinical Casebook Project (MCCP).

Effects of palytoxin on cation occlusion and phosphorylation of the (Na+,K+)-ATPase.

Palytoxin (PTX) inhibits the (Na(+) + K+)-driven pump and simultaneously opens channels that are equally permeable to Na+ and K+ in red cells and other cell membranes. In an effort to understand the mechanism by which PTX induces these fluxes, we have studied the effects of PTX on: 1) K+ and Na+ occlusion by the pump protein; 2) phosphorylation and dephosphorylation of the enzyme when a phosphoenzyme is formed from ATP and from P(i); and 3) p-nitro phenyl phosphatase (p-NPPase) activity associated with the (Na+, K+)-ATPase. We have found that palytoxin 1) increases the rate of deocclusion of K+(Rb+) in a time- and concentration-dependent manner, whereas Na+ occluded in the presence of oligomycin is unaffected by the toxin; 2) makes phosphorylation from P(i) insensitive to K+, and 3) stimulates the p-NPPase activity.

Ion channels formed by transcription factors recognize consensus DNA sequences.

Transcription factors (TFs) are proteins which bind to specific DNA sequences and thus participate in the regulation of the initiation of transcription. We report in this communication our observations that several of these proteins interact with lipid membranes and form ion-permeable channels. For each of the TFs that we studied, the single channel conductance was distinctively different, i.

How one teaching hospital system and one medical school are jointly affirming their academic mission.

The economic forces that are reshaping the practice of medicine and the funding of medical research will have great impact on clinical education and research in teaching hospitals and their associated medical schools. Changes in the setting of and approach to medical education will need to be made in order to continue to train physicians at the same high level as in the past and to maintain the productivity of our national biomedical research enterprise and its contributions to health. Academic leaders, such as department chiefs who have clinical service responsibilities, are finding it more and more difficult to manage simultaneously the demands of the clinical business, education, and research.

Interaction of palytoxin with red cells: structure-function studies.

Palytoxin (PTX), a potent toxin isolated from the marine soft coral Palythoa tuberculosa increases the cationic permeability of red cell membranes and inhibits the (Na+,K+)-activated ATPase, effects that are completely reversed by ouabain. It has also been shown to compete with ouabain for a binding site and it has been suggested that it binds to the Na+,K(+)-pump molecule in cells. In a search for analogues of PTX that would bind covalently and could thus be used to identify and characterize the binding site, we have used compounds which differed from PTX at one end or at both ends simultaneously.

Inhibition of the actions of palytoxin on the K+ efflux from red cells and on the Na/K-ATPase activity by a monoclonal antibody.

Palytoxin (PTX) binds to the Na/K pump, inhibits the (Na/K)-ATPase and forms Na and K permeable channels in human red cells. Here, we report that a monoclonal antibody raised against a derivative of PTX (Bignami, G.S.

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.

CD4+ lipid bilayers. A model for human immunodeficiency virus type 1 coat protein binding.

gp120, the coat glycoprotein of the human immunodeficiency virus type 1 (HIV1) binds to a molecule on the surface of a class of T-lymphocytes, CD4, which is also the receptor for major histocompatibility complex class II (MHCII). To study the events that follow the interaction of gp120 with CD4, we have incorporated CD4 into lipid bilayers and recorded the electrical changes which occur after the addition of gp120. Interaction of gp120 to CD4-containing bilayers induces multistate ion-permeable channels with a maximum conductance of 380-400 picosiemens.

Primary structure of peptides and ion channels. Role of amino acid side chains in voltage gating of melittin channels.

Melittin produces a voltage-dependent increase in the conductance of planar lipid bilayers. The conductance increases when the side of the membrane to which melittin has been added (cis-side) is made positive. This paper reports observations on the effect of modifying two positively charged amino acid residues within the NH2-terminal region of the molecule: lysine at position 7 (K7), and the NH2-terminal glycine (G1).

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.

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.

Acid pH induces formation of dense cells in sickle erythrocytes.

When erythrocytes from patients homozygous for hemoglobin S (SS) are swollen or exposed to pH less than 7.40, they lose K, Cl, and water through a volume and pH-dependent KCl cotransport system. We report that carbon monoxide-treated SS cells become progressively denser when incubated for eight to 12 hours in media with pH less than 7.

Role of chloride in potassium transport through a K-Cl cotransport system in human red blood cells.

In this paper, we report experiments demonstrating the coupling of Cl and K movements in a volume-dependent K-Cl cotransport system in human red blood cells. We show that an outwardly directed Cl gradient can promote net K efflux against an inwardly directed K gradient at constant membrane potential. Red blood cell membrane potential was kept constant by using anions that are not transported through the K-Cl cotransport system but that are more permeable than Cl (NO3 and SCN).

Voltage-gated channels formed in lipid bilayers by a positively charged segment of the Na-channel polypeptide.

The Na-channel polypeptide is responsible for the voltage-gated and time-dependent ionic permeability changes that give rise to the action potential in the membranes of nerve cells. We have synthesized a 22-amino acid peptide with a sequence identical to that of the segment named S4, repeat IV of the primary structure of the Na channel. We have found that this peptide induces a voltage- and time-dependent conductance in bilayers formed by a mixture of phosphatidyl-ethanolamine and phosphatidylserine.

Properties of K+ transport in resealed human erythrocyte ghosts.

We report here our studies on K+ transport in resealed human red cell ghosts (RG) in the presence of 0.1 mM ouabain and 0.01 mM bumetanide, inhibitors of the Na+-K+ pump and Na+-K+-Cl- cotransport, respectively.

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.

Effects of pH, potential, chloride and furosemide on passive Na+ and K+ effluxes from human red blood cells.

Ouabain-resistant effluxes from pretreated cells containing K+/Na+ = 1.5 into K+ and Na+ free media were measured. Furosemide-sensitive cation effluxes from cells with nearly normal membrane potential and pH were lower in NO3- media than in Cl- media; they were reduced when pH was lowered in Cl- media.

The synthetic precursor specific region of pre-pro-parathyroid hormone forms ion channels in lipid bilayers.

We have used the chemically synthesized sequence of pre-pro-parathyroid hormone and several of its analogues to test the notion that the capacity of amphipathic peptides to aggregate in membranes and form ion-permeable channels correlates with their ability to function as signal sequences for secreted proteins. We found that pre-pro-parathyroid hormone (the signal sequence and pro-region of parathyroid hormone (M], as well as some of its analogues, forms aggregates of monomers which are ion-permeable. The ion-permeable aggregates (2-3 monomers) formed by (M) are voltage-dependent and are more permeable for cations than for anions.