A technique for automatic tubing occlusion in response to air bubble detection when using a centrifugal pump.

A double acting pneumatically powered cylinder, energized by an electrically activated solenoid valve, is used to occlude the outflow line from a Bio-Medicus (a) constrained vortex pump. The cylinder is mounted on a tubing guide that is fastened to a pole clamp. A Sarns (b) air bubble detector, placed on the pump inflow line is used to provide the signal to activate the solenoid valve. The outflow occluder is capable of 100% occlusion of 3/8 x 3/32 inch Tygon tubing up to pressures of 2586 mmHg. The occluder system is able to work with many types of bubble detectors and is applicable to any form of non-occlusive pump.

Hydrolysis of a series of synthetic peptide substrates by the human rhinovirus 14 3C proteinase, cloned and expressed in Escherichia coli.

The 3C proteins of several picornaviruses, including poliovirus, foot-and-mouth disease virus (FMDV) and encephalomyocarditis virus (EMCV), have been demonstrated to be cysteine-type proteinases, involved in the processing of the respective polyproteins expressed by the monocistronic RNA genome. Nucleotide sequencing data have indicated that the human rhinovirus 14 (HRV-14) RNA genome encodes a homologous 3C protein. The HRV-14 3C protein was purified to homogeneity from Escherichia coli expressing the cloned 3C genomic fragment. The enzyme was assayed against peptides corresponding to those residues, predicted (by nucleotide sequencing data) to occur at authentic cleavage sites within the polyprotein. The peptides representing the 1B/1C, 2A/2B, 2C/3A, 3A/3B, 3B/3C and 3C/3D cleavage sites, where proteolysis was predicted to occur at a Gln-Gly junction, were all cleaved by the 3C proteinase. The hydrolysis was shown (by reverse phase fast protein liquid chromatography and amino acid analysis) to occur specifically at the Gln-Gly bond in each of the peptides. The ready availability of such convenient substrates facilitated the further characterization of the 3C proteinase. By contrast, peptides corresponding to the predicted 2B/2C and 1C/1D cleavage sites, where the processing was presumed to occur at a Gln-Ala or Glu-Gly bond respectively, were not cleaved by the 3C proteinase. The ability of the HRV-14 3C proteinase to hydrolyse the synthetic peptides was inhibited if a Cys----Ser(146) mutation was introduced into the protein. Studies with known proteinase inhibitors substantiated the conclusion that the HRV-14 3C protein appears to be a cysteine proteinase and that the Cys residue at position 146 may be the active site nucleophile. The HRV-14 3C proteinase probably plays an important role, analogous to that implied for the poliovirus 3C proteinase, in the replication of the virus and thus represents a potential target for antiviral chemotherapy.

A consensus sequence for substrate hydrolysis by rhinovirus 3C proteinase.

Kinetic constants were determined for the hydrolysis of a series of synthetic peptide substrates by recombinant rhinovirus (HRV 14) 3C proteinase. Systematic removal or replacement of individual residues indicated that the minimum sequence required for effective cleavage by the viral cysteine proteinase was P5-Val/Thr-P3-P2-Gln-Gly-Pro.

Interactions between extraocular proprioceptive and visual signals in the superior colliculus of the cat.

1. The responses of units in the superficial layers of the superior colliculus to stretch of extrinsic ocular muscles (e.o.m.) and to visual stimuli, delivered singly and paired at various inter-stimulus intervals, were studied in chloralose-anaesthetized cats. 2. Most units responded to visual stimuli and about half also gave phasic excitatory responses to stretch of e.o.m. 3. Signals from the e.o.m. of each eye reach both superior colliculi; only those in the colliculus ipsilateral to the e.o.m. stretched were studied in detail. 4. A variety of control experiments provided evidence that the signal leading to the responses to e.o.m. stretch was extraretinal. The strong probability is that the receptors responsible were in the extrinsic ocular muscles or their tendons. 5. Of fifty-six units, twenty-four (43%) showed definite interactions between the effects of visual stimuli delivered to the left eye and those due to stretch of e.o.m. of the right eye whose retina had been destroyed. 6. Interactions were found with both stationary and moving visual stimuli. They involved either enhancement or reduction (sometimes abolition) of the response to either e.o.m. or visual stimulation, particularly the latter. 7. Units with interactions showed one of three types of behaviour. (1) Excitatory responses to visual and e.o.m. stimuli given singly, and interactions when the two types of stimulus were paired at some time intervals. Suppression and abolition of visual responses by preceding e.o.m. stretch was common. (2) Units with little or no excitatory response to e.o.m. stretch applied alone, but with showed reduction of their visual responses by preceding e.o.m. stretch. (3) Units with minimal responses to either type of stimulus presented alone but which gave markedly enhanced responses when visual and e.o.m. stimuli were paired. 8. These interactions between proprioceptive and retinal signals are thought to allow retinal image movements which result from saccades to be distinguished from those due to movement of objects in the external world.