Induction of apoptosis by a Newcastle disease virus vaccine (MTH-68/H) in PC12 rat phaeochromocytoma cells.

The attenuated Newcastle Disease Virus (NDV) vaccine MTH-68/H has been found to cause regression of various tumors including certain types of human neoplasms (See Table 1 and References 86-88). The mechanism of its oncolytic action is poorly understood, but it appears to affect specific signaling pathways in the target cell. We studied the cellular effects of NDV employing PC12 rat phaeochromocytoma cells, a widely used model system to analyze differentiation, proliferation and apoptosis. The MTH-68/H vaccine was found to be cytotoxic on PC12 cells. It caused internucleosomal DNA fragmentation, the most characteristic feature of programmed cell death (PCD). A brief exposure (30 min) of P12 cells to the virus was sufficient to produce a full-blown apoptotic response. Major mitogen-activated protein kinase pathways (including the stress inducible c-Jun N-terminal kinase pathway and p38 pathway) or mechanisms regulated by reactive oxygen species appear to have no role in virus-induced cell death. The PCD-inducing effect of MTH-68/H could not be prevented by simultaneous treatment of the P12 cells with growth factors or second messenger analogs stimulating protein kinase C or Ca(++)-mediated pathways. In contrast, treatment with a cyclic AMP analog partially protected the them from virus-induced apoptosis. These experimental results suggests that MTH-68/H might disrupt a growth factor-stimulated survival pathway and that direct stimulation of protein kinase A-catalyzed phosphorylation events bypass this NDV-induced block.

Local anesthetics inhibit receptors coupled to phosphoinositide signaling in Xenopus oocytes.

Effects and the mechanism of action of quaternary amine local anesthetics on ligand- and voltage-activated ion currents were studied using voltage-clamped ovarian follicles and oocytes from Xenopus laevis. The fast inward and slow outward currents in response to acetylcholine were unaltered by procaine, whereas the oscillatory and smooth inward chloride currents (ICl) were abolished. Potassium currents (IK) elicited by norepinephrine and oscillatory ICl elicited by lysophosphatidic acid were blocked. Procaine caused a noncompetitive inhibition of oscillatory ICl mediated by heterologously expressed neurotransmitter receptors from the rat brain. Threefold differences were found in the procaine sensitivity of the 5-HT2a and 5-HT2c receptors. The rank order of intrinsic inhibitory activity of local anesthetics was: procaine > lidocaine > dibucaine > tetracaine. Extra- or intracellular application of procaine did not alter the Ca2+-activated Cl- current, indicating that neither the endogenous voltage-gated Ca2+ nor the Ca2+-activated Cl- channels account for the inhibition. Procaine caused only a slight reduction in ICl elicited by photolysis of caged inositol 1,4,5-trisphosphate (InsP3) and did not abolish ICl triggered by GTP[gamma-S]-induced direct activation of G proteins. For receptors coupling to the phosphoinositide/Ca2+ signal transduction pathway, the primary and physiologically relevant site of procaine action appears to be on the extracellular surface, upstream from the G protein, presumably on the receptor.

Activation heat in various cross-striated muscles of Rana esculenta: microcalorimetric measurements.

Activation heat (AH) is an important component in energy balance of muscle contraction. It represents energy dissipation of biochemical processes enabling muscle in rest to perform contraction. According to our measurements on intact muscles, AH is 20% of initial heat production in twitch, and 10% in tetanus. Significantly different AH values have been obtained for muscles of parallel and not parallel fibre architecture.

The study of nitroxide radical active esters as spin labels on muscle protein actin.

Nitroxide radical active esters were used to label the muscle protein actin and to study the orientation dependence of the EPR spectra of the labelled protein. It is concluded that the labels are located at least at two different sites of the protein with strong polar environment and different mobilities. The EPR spectrum of the strongly immobilized labels exhibits orientation dependence, the N--O bond axis of the spin labels is nearly perpendicular to the long axis of the F-actin threads, and the labels undergo a rapid rotational motion about an axis directed perpendicular to the filament axis. The application of the nitroxide radical active esters may be useful in the study of ordered systems as muscle or muscle protein systems.

Dependence of the heat production of active muscle on the length of muscle.

The dependence of the heat production of muscle on length was examined in isometric (with stretch) and isotonic (free of stretch) tetanuses of 2 s. The isometric heat production was significantly greater than the isotonic one at any length of muscle. The isometric heat coefficient (Flo/Q, where F is the active tension development of muscle measured in ponds, lo is the resting length measured in cm, Q is the heat production during the contraction at a given length measured in mcal) was not constant but dependent on the length of muscle, and had an extreme value near the resting length (lo). A close positive correlation was found between the active tension development and the heat production of the muscle.