Peptide sequencing in an electrolytic cell with two nanopores in tandem and exopeptidase

A nanopore-based approach to peptide sequencing without labels or immobilization is considered. It is based on a tandem cell (RSC Adv., 2015, 5, 167-171) with the structure [cis1, upstream pore (UNP), trans1/cis2, downstream pore (DNP), trans2]. An amino or carboxyl exopeptidase attached to the downstream side of UNP cleaves successive leading residues in a peptide threading from cis1 through UNP. A cleaved residue translocates to and through DNP where it is identified. A Fokker-Planck model is used to compute translocation statistics for each amino acid type. Multiple discriminators, including a variant of the current blockade level and translocation times through trans1/cis2 and DNP, identify a residue. Calculations show the 20 amino acids to be grouped by charge (+, -, neutral) and ordered within each group (which makes error correction easier). The minimum cleaving interval required of the exopeptidase, the sample size (number of copies of the peptide to sequence or runs with one copy) to identify a residue with a given confidence level, and confidence levels for a given sample size are calculated. The results suggest that if the exopeptidase cleaves each and every residue and does so in a reasonable time, peptide sequencing with acceptable (and correctable) errors may be feasible. If validated experimentally the proposed device could be an alternative to mass spectrometry and gel electrophoresis. Implementation-related issues are discussed.

Continuous spinal anesthesia versus combined spinal epidural block for major orthopedic surgery: prospective randomized study

CONTEXT AND OBJECTIVES: In major orthopedic surgery of the lower limbs, continuous spinal anesthesia (CSA) and combined spinal epidural anesthesia (CSE) are safe and reliable anesthesia methods. In this prospective randomized clinical study, the blockading properties and side effects of CSA were compared with single interspace CSE, among patients scheduled for major hip or knee surgery. DESIGN AND SETTING: Prospective clinical study conducted at the Institute for Regional Anesthesia, Hospital de Base, São José do Rio Preto. METHODS: 240 patients scheduled for hip arthroplasty, knee arthroplasty or femoral fracture treatment were randomly assigned to receive either CSA or CSE. Blockades were performed in the lateral position at the L3-L4 interspace. Puncture success, technical difficulties, paresthesia, highest level of sensory and motor blockade, need for complementary doses of local anesthetic, degree of technical difficulties, cardiocirculatory changes and postdural puncture headache (PDPH) were recorded. At the end of the surgery, the catheter was removed and cerebrospinal fluid leakage was evaluated. RESULTS: Seven patients were excluded (three CSA and four CSE). There was significantly lower incidence of paresthesia in the CSE group. The resultant sensory blockade level was significantly higher with CSE. Complete motor blockade occurred in 110 CSA patients and in 109 CSE patients. Arterial hypotension was observed significantly more often in the CSE group. PDPH was observed in two patients of each group. CONCLUSION: Our results suggest that both CSA and CSE provided good surgical conditions with low incidence of complications. The sensory blockade level and hemodynamic changes were lower with CSA.