The deduced amino acid sequence of a Drosophila gene isolated with a vertebrate sodium channel complementary DNA probe revealed an organization virtually identical to the vertebrate sodium channel protein; four homologous domains containing all putative membrane-spanning regions are repeated in tandem with connecting linkers of various sizes. All areas of the protein presumed to be critical for channel function show high evolutionary conservation. These include those proposed to function in voltage-sensitive gating, inactivation, and ion selectivity. All 24 putative gating charges of the vertebrate protein are in identical positions in the Drosophila gene. Ten introns interrupt the coding regions of the four homology units; introns with positions conserved among homology units bracket a region hypothesized to be the selectivity filter for the channel. The Drosophila gene maps to the right arm of the second chromosome in region 60D-E. This position does not coincide with any known mutations that confer behavioral phenotypes, but is close to the seizure locus (60A-B), which has been hypothesized to code for a voltage-sensitive sodium channel.
The current-voltage (I-V) relationship for acetylcholine-elicited currents in the rat pheochromocytoma cell line PC12 is nonlinear. Two voltage-dependent processes that could account for the whole-cell current rectification were examined, receptor channel gating and single receptor channel permeation. We found that both factors are involved in the rectification of the whole-cell currents. The voltage dependence of channel gating determines the shape of the I-V curve at negative potentials. The single-channel I-V relationship is inwardly rectifying and largely responsible for the characteristic shape ofthe whole-cell I-V curve at positive potentials. Johnson, Washington University School of Medicine). Cultures were fed three times a week and used 5-10 days after plating.Physiological Recordings. Recordings were obtained using the List EPC-7 patch clamp. Records from whole-cell and outside-out patches (12) were acquired using the PCLAMP programs (Axon Instruments, Foster City, CA) and a 386 Zenith personal computer. Data were analyzed using BINFITS (C. Lingle, Washington University School of Medicine). Pipettes were pulled from KG33 borosilicate capillaries by using a P-80/PC micropipette puller (Sutter Instrument, San Rafael, CA) and coated with Sylgard 182 (Dow). After fire-polishing, pipette resistances were 2-5 MQ when the pipettes were filled with sodium isethionate intracellular solution (see below). For whole-cell recordings, the EPC-7 circuitry was used to cancel the capacity charging transients and to compensate for the series resistance, which ranged from 5 to 30 MQ. Series resistances were 70-80% compensated. Whole-cell and single-channel records were filtered at 2 kHz with an eight-pole low-pass Bessel filter. All experiments were conducted at room temperature (18-19'C) unless specified otherwise.Whole-cell I-V relationships were determined from peak currents elicited by ACh application to cells held at various potentials between -80 and +80 mV.Voltage-jump records were obtained by bracketing a series of jumps in the presence of ACh with jumps done in the absence of agonist. Voltage-jump records were leaksubtracted averages of 12-18 jumps. Current relaxations were fit with a single exponential or the sum of two exponential components by using the BINFITS program. Best fits were determined by visual inspection.Single-channel I-V relationships were determined using voltage ramps and voltage jumps. An AI2020 event detector (Axon Instruments, Foster City, CA) was used to trigger the computer to initiate the voltage ramp or jump when a single Abbreviations: ACh, acetylcholine; SCG, superior cervical ganglion;I-V, current-voltage.
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Guidewire retention is a rare complication of central venous catheter placement, and has been related to operator fatigue, inexperience, and inattention, and inadequate supervision of trainees. The true incidence of guidewire loss after intraoperative placement of central venous catheters is unknown. We report 4 cases of guidewire loss after central venous access procedures performed by anesthesia providers in the operating room. Worsening of patients' clinical condition during catheter placement and complex procedures necessitating more than one guidewire insertion are recurring scenarios in cases involving guidewire loss. Over 6 years at our institution, intraoperative wire loss occurred at a rate of 1:3291 procedures (95% confidence interval of 1/10,000 to 8/10,000).
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