Brian Whiteley

Chapter 1 Mitogens and Ion Fluxes

Publisher Summary This chapter discusses the mechanisms of the transport of Na + , K + , Cl – , Ca 2+ , and H + by cell membranes and the mechanisms of the maintenance and regulation of cell volume, intracellular pH, and intracellular Ca 2+ activity. The action of mitogens in controlling these processes is reviewed, and the transport across intracellular membranes and the interrelationships between the transport of different substrates is also discussed. Inhibitors are powerful experimental tools in the study of membrane transport processes. However, two kinds of problems are frequently faced when employing these agents. The first problem is related to the lack of specificity of some of these agents and the second problem is related to the lack of consideration of secondary effects. Mitogen-cell interactions are highly complex and subject to both positive and negative regulation. Mitogens alter the rate of various ionic fluxes into cells. For example, Ca 2+ entry increases as a result of the addition of mitogens to cells.

Modulation of the activity of the platelet-derived growth factor receptor by phorbol myristate acetate

Phorbol myristate acetate (PMA) weakly activates Na+/H+ exchange in NR-6 cells. Simultaneously, PMA blocks the activation of Na+/H+ exchange by platelet-derived growth factor or by serum. Phorbol esters that do not activate protein kinase C do not show this metabolic response. We conclude that activation of Na+/H+ exchange by platelet-derived growth factor or serum does not require the intermediate activation of protein kinase C. We postulate from this and previous observations that a major role of protein kinase C is to act as an inhibitor of the activity of cell surface receptors, in particular mitogen receptors.

Chapter 9 Control of Mitogenic Activation of Na+-H+ Exchange

Publisher Summary Among the earliest events that follow the binding of mitogens to cell surface receptors is the activation of a variety of transport systems, including those for Na + , K + , Ca 2+ , phosphate, glucose, amino acids, and uridine. The activation of some of these transport events is extremely rapid. The activation of some or all of these transport systems may be permissive for the cells to traverse the cell cycle, but activation of any one of these transport systems is not sufficient by itself to drive the cells through the cell cycle. A convenient method for the measurement of Na + –H + exchange in cells is the use of a dye whose fluorescence is pH sensitive and can be used to determine changes in cytoplasmic pH. Optical methods provide sensitivity and temporal resolution for such measurements. The dye should be nontoxic and have a structure that allows it to be permanently retained in the cytoplasm; that is, the leakage rate should be negligible during the time of the experiment. pH i and Na + –H + exchange activity are controlled, following the addition of mitogens to cells. Protein kinase C acts to modulate the activity of a variety of mitogen receptors, and the tyrosine kinase activity of these receptors is required for their activation of the Na + –H + exchange molecule. The activation of protein kinase C inactivates the epidermal growth factor (EGF) receptor as a tyrosine kinase. EGF activates phosphatidylinositol breakdown in A431 cells, and platelet-derived growth factor (PDGF) has this effect in 3T3 fibroblasts. Thus, each of these mitogens activates an enzyme that renders the mitogen receptor nonfunctional.

Excited state dynamics of metalloporphyrins in the gas phase

Abstract The role of a condensed phase medium in the ultrafast dynamics of metalloporphyrins is studied with gas phase experiments aimed at probing dissipation of excess vibrational energy from optically excited porphyrins and how excess vibrational energy is manifested in the electronic absorption and emission spectra of these complexes. Preliminary results reveal unexpected effects of the medium on the optical spectra and dynamics.