Current indications for left thoracotomy in coronary revascularization and valvular procedures

BACKGROUND

Left thoracotomy is infrequently used for cardiac procedures, but its application in reoperative and minimally invasive coronary revascularization and in valvular procedures has been reported recently.

METHODS

Three case reports and a review of the current literature illustrate the unique benefits of this approach for myocardial revascularization and valve replacement.

RESULTS

Reoperative coronary revascularization of the left anterior descending and circumflex coronary arteries was performed off-pump via a left posterolateral thoracotomy. For the second case, this approach was used for coronary artery bypass grafting of the right coronary and left anterior descending arteries with femoral-femoral cardiopulmonary bypass in a patient with congestive heart failure and coronary artery disease who also required closure of a patent ductus arteriosus. In the third case, mitral valve replacement using femoral venous and aortic cannulation for cardiopulmonary bypass was performed via a left thoracotomy to avoid a retrosternal gastric conduit in a patient with severe mitral stenosis and congestive heart failure. All patients returned to normal activity and are asymptomatic.

CONCLUSIONS

These case reports and a comprehensive review of the literature demonstrate the utility of left thoracotomy as an alternative approach to standard median sternotomy in selected cases of revascularization and valvular procedures.

Open access capillary electrophoresis. A walk up capillary electrophoresis service for the synthetic chemist

A capillary electrophoresis (CE) system has been developed to provide routine purity information to support synthetic organic chemists. A single micellar electrokinetic chromatography system that produces good selectivity with short run times was developed. The instrument operating software has been modified to run separations in a custom open access mode. No expert knowledge of CE is required to run separations.

Activation of NF-kappaB by PM(10) occurs via an iron-mediated mechanism in the absence of IkappaB degradation

Exposure to particulate air pollution (PM(10)) is associated with exacerbations of respiratory diseases and increased cardiopulmonary mortality. PM(10) induces lung inflammation in rats, which has been attributed to many factors, including the ultrafine components of PM(10), endotoxins, and transition metals. In this study, we investigated in alveolar epithelial (A549) cells whether PM(10) could activate nuclear factor-kappa B (NF-kappaB), a transcription factor stimulated in response to many proinflammatory agents. Our results show that PM(10) samples from various sites within the United Kingdom cause nuclear translocation, DNA-binding, and transcriptional activation of NF-kappaB in A549 cells. Furthermore, increased NF-kappaB activity was observed in the absence of IkappaB degradation. To evaluate the role of iron, A549 cells were exposed to PM(10) previously treated with phosphate-buffered saline (PBS), deferoxamine mesylate, or deferoxamine plus ferrozine. PBS-treated and, to a lesser extent, deferoxamine-treated PM(10) were able to activate NF-kappaB, whereas this response was completely abrogated in cells exposed to PM(10) treated with both deferoxamine and ferrozine. Moreover, we studied the effects of soluble components of PM(10) on NF-kappaB activation by exposing alveolar epithelial cells to soluble fractions from PM(10) treated with PBS or the metal chelators. We found that, compared with fractions from PBS-treated PM(10) which activated NF-kappaB, fractions from PM(10) treated with deferoxamine and ferrozine did not stimulate NF-kappaB activity above background levels. Coincubation of polymixin B, an endotoxin-binding compound, and PM(10) did not inhibit NF-kappaB. In summary, PM(10) activates NF-kappaB in A549 cells by an iron-mediated mechanism in the absence of IkappaB degradation.

Inhibition of potassium and calcium currents in neurones by molecularly-defined P2Y receptors

Messenger RNAs and cDNAs for individual cloned P2Y(1), P2Y2 and P2Y(6) nucleotide receptors have been expressed by micro-injection into dissociated rat superior cervical sympathetic neurones and the effects of stimulating the expressed receptors on voltage-activated N-type Ca(2+) currents and M-type K(+) currents recorded. Both currents were reduced by stimulating all three receptors, with the following mean IC(50) values: P2Y(1) (agonist: ADP) - I(K(M)) 6.9 nM, I(Ca) 8.2 nM; P2Y(2) (agonist: UTP) - I(K(M)) 1.5 microM, I(Ca) 0.5 microM; P2Y(6) (agonist: UDP) - I(K(M)) 30 nM, I(Ca) 5.9 nM. Inhibition of I(K(M)) was voltage-independent and insensitive to Pertussis toxin; inhibition of I(Ca) showed both voltage-sensitive and insensitive, and Pertussis toxin-sensitive and insensitive components. It is concluded that these P2Y receptors can couple to more than one G protein and thereby modulate more than one ion channel. It is suggested that these effects on K(M) and Ca(N) channels may induce both postsynaptic excitory and presynaptic inhibitory responses.

Determination of the dynamic elastic moduli and internal friction using thin resonant bars

Analysis of the data from the resonant-bar technique for determining wave speed and internal friction is presented. Internal friction has been included in the longitudinal and torsional wave equations and the analytical solution has been obtained. In determining the acoustical constants of lossy materials, a broad frequency spectrum is used that includes many resonances and not just data at or near the individual resonances. Corrections due to the mass, length, stiffness, and damping of the transducers are also presented. The theoretical solutions are compared with the measured magnitude and phase response data for torsional, longitudinal, and flexural measurements and are shown to be in good agreement.

Motor vehicle manufacturing and prostate cancer

BACKGROUND

The purpose of this investigation was to evaluate the relation between employment in motor vehicle manufacturing (MVM) and fatal prostate cancer.

METHODS

The study included 322 prostate cancer deaths occurring in 1973 through 1987 and 1,285 controls, selected from a cohort of 126,100 male MVM workers.

RESULTS

Men employed in casting operations had an odds ratio of 1.5 (95% CI = 1. 1-2.0). The association was consistent across casting facilities and was attributable primarily to work in core and mold making (OR = 1.5, 95% CI = 1.1-2.2) and metal melting and pouring jobs (OR = 1.9, 95% CI = 1.0-3.6). Other results included ORs of 1.9 (95% CI = 1.0-3.7) for warehousing and distribution operations and 2.1 (95% CI = 1.2-3. 7) for electric and electronic equipment manufacturing. The latter two associations exhibited little internal consistency.

CONCLUSIONS

The relationships seen in this study were weak and may have been due to chance. Core and mold making and metal melting and pouring foundry operations entail potential exposure to metal dusts and fumes, to polycyclic aromatic hydrocarbons (PAHs), and to other chemicals. However, associations between these exposures and prostate cancer have not been reported consistently, nor have other studies of foundry workers consistently noted an excess of prostate cancer.

Calcium channel gating and modulation by transmitters depend on cellular compartmentalization

Voltage-gated Ca2+ channels participate in dendritic integration, yet functional properties of Ca2+ channels and mechanisms of their modulation by neurotransmitters in dendrites are unknown. Here we report how pharmacologically identified Ca2+ channels behave in different neural compartments. Whole-cell and cell-attached patch-clamp recordings were made on both cell bodies and electrically isolated dendrites of sympathetic neurons. We found not only that Ca2+ channel populations differentially contribute to somatic and dendritic currents but also that families of Ca2+ channels display gating properties and neurotransmitter modulation that depend on channel compartmentalization. By comparison with their somatic counterparts, dendritic N-type Ca2+ currents were hypersensitive to neurotransmitters and G proteins. Single-channel analysis showed that dendrites express a unique N-type channel that has enhanced interaction with Gbetagamma. Thus Ca2+ channels in dendrites seem to be specialized elements with unique regulatory mechanisms.

Neurobiology: the acid test for resting potassium channels

The K(+) channels that generate the resting potential of mammalian neurons have been difficult to identify and characterize. Recent experiments on hypoglossal motoneurons and cerebellar granule cells suggest that the resting current in these neurons is carried by TASK-1, a member of the twin-pore family of K(+) channels.

Muscarinic inhibition of calcium current and M current in Galpha q-deficient mice

Activation of M(1) muscarinic acetylcholine receptors (M(1) mAChR) inhibits M-type potassium currents (I(K(M))) and N-type calcium currents (I(Ca)) in mammalian sympathetic ganglia. Previous antisense experiments suggested that, in rat superior cervical ganglion (SCG) neurons, both effects were partly mediated by the G-protein Galpha(q) (Delmas et al., 1998a; Haley et al., 1998a), but did not eliminate a contribution by other pertussis toxin (PTX)-insensitive G-proteins. We have tested this further using mice deficient in the Galpha(q) gene. PTX-insensitive M(1) mAChR inhibition of I(Ca) was strongly reduced in Galpha(q) -/- mouse SCG neurons and was fully restored by acute overexpression of Galpha(q). In contrast, M(1) mAChR inhibition of I(K(M)) persisted in Galpha(q)-/- mouse SCG cells. However, unlike rat SCG neurons, muscarinic inhibition of I(K(M)) was partly PTX-sensitive. Residual (PTX-insensitive) I(K(M)) inhibition was slightly reduced in Galpha(q) -/- neurons, and the remaining response was then suppressed by anti-Galpha(q/11) antibodies. Bradykinin (BK) also inhibits I(K(M)) in rat SCG neurons via a PTX-insensitive G-protein (G(q) and/or G(11); Jones et al., 1995). In mouse SCG neurons, I(K(M)) inhibition by BK was fully PTX-resistant. It was unchanged in Galpha(q) -/- mice but was abolished by anti-Galpha(q/11) antibody. We conclude that, in mouse SCG neurons (1) M(1) mAChR inhibition of I(Ca) is mediated principally by G(q), (2) M(1) mAChR inhibition of I(K(M)) is mediated partly by G(q), more substantially by G(11), and partly by a PTX-sensitive G-protein(s), and (3) BK-induced inhibition of I(K(M)) is mediated wholly by G(11).

Contralateral movement and extensor force generation alter flexion phase muscle coordination in pedaling

The importance of bilateral sensorimotor signals in coordination of locomotion has been demonstrated in animals but is difficult to ascertain in humans due to confounding effects of mechanical transmission of forces between the legs (i.e., mechanical interleg coupling). In a previous pedaling study, by eliminating mechanical interleg coupling, we showed that muscle coordination of a unipedal task can be shaped by interlimb sensorimotor pathways. Interlimb neural pathways were shown to alter pedaling coordination as subjects pedaling unilaterally exhibited increased flexion-phase muscle activity compared with bilateral pedaling even though the task mechanics performed by the pedaling leg(s) in the unilateral and bilateral pedaling tasks were identical. To further examine the relationship between contralateral sensorimotor state and ipsilateral flexion-phase muscle coordination during pedaling, subjects in this study pedaled with one leg while the contralateral leg either generated an extensor force or relaxed as a servomotor either held that leg stationary or moved it in antiphase with the pedaling leg. In the presence of contralateral extensor force generation, muscle activity in the pedaling leg during limb flexion was reduced. Integrated electromyographic activity of the pedaling-leg hamstring muscles (biceps femoris and semimembranosus) during flexion decreased by 25-30%, regardless of either the amplitude of force generated by the nonpedaling leg or whether the leg was stationary or moving. In contrast, rectus femoris and tibialis anterior activity during flexion decreased only when the contralateral leg generated high rhythmic force concomitant with leg movement. The results are consistent with a contralateral feedforward mechanism triggering flexion-phase hamstrings activity and a contralateral feedback mechanism modulating rectus femoris and tibialis anterior activity during flexion. Because only muscles that contribute to flexion as a secondary function were observed, it is impossible to know whether the modulatory effect also acts on primary, unifunctional, limb flexors or is specific to multifunctional muscles contributing to flexion. The influence of contralateral extensor-phase sensorimotor signals on ipsilateral flexion may reflect bilateral coupling of gain control mechanisms. More generally, these interlimb neural mechanisms may coordinate activity between muscles that perform antagonistic functions on opposite sides of the body. Because pedaling and walking share biomechanical and neuronal control features, these mechanisms may be operational in walking as well as pedaling.

Adiposity does not hinder the fitness response to exercise training in obese women

BACKGROUND

This study examined how sedentary obese (OB) and normal weight (NW) women respond to exercise training; and if fitness levels of the OB and NW are comparable, in spite of differences in adiposity.

METHODS

Sedentary OB (n=46, 48.5+/-1.5 yrs, BMI=35.9+/-0.8; mean+/-SEM) and NW (n=43, 48.3+/-1.7 yrs, BMI=21.7+/-0.2) women participated in a 14-week fitness program.

RESULTS

There were no group differences in exercise adherence. No changes for either group were found for body weight or composition. Both groups improved similarly in aerobic fitness (VO2max), muscular strength (grip strength), muscular endurance (modified push-up), and flexibility (sit and reach). However, since norms for fitness are generally expressed relative to body weight (e.g. VO2max, ml x kg(-1) x min(-1); grip strength ratios), the OB women continued to be classified as unfit after exercise training, and categorized below the NW women in spite of having absolute scores for VO2max (OB=2.1+/-0.1, NW=1.8+/-0.1 l x min(-1)) and grip strength (OB=65.1+/-1.5, NW= 58.6+/-1.5 kg) that were higher than the NW women.

CONCLUSIONS

The data suggest that OB women respond in a similar manner as NW women to exercise; that weight loss is not necessary for improved fitness; and that the OB are not less fit than the NW, but that low fitness scores for the OB are simply a reflection of the absolute scores being deflated because they are proportioned to body weight.

The propeptide of macrophage inhibitory cytokine (MIC-1), a TGF-beta superfamily member, acts as a quality control determinant for correctly folded MIC-1

Macrophage inhibitory cytokine (MIC-1), a divergent member of the transforming growth factor-beta (TGF-beta) superfamily and activation associated cytokine, is secreted as a 28 kDa dimer. To understand its secretion, we examined its processing in MIC-1-transfected Chinese hamster ovary cells. Mature MIC-1 dimer arises post-endoplasmic reticulum (ER) by proteolytic cleavage of dimeric pro-MIC-1 precursor at a furin-like site. Unlike previously characterized TGF-beta superfamily members, MIC-1 dimers are also secreted in constructs lacking the propeptide. A clue to the function of the propeptide came from the observation that a range of proteasome inhibitors, including lactacystin and MG132, cause major increases in levels of undimerized pro-MIC-1 precursor. There was no effect of proteasome inhibitors on cells expressing mature MIC-1 without the propeptide, suggesting that the propeptide can signal misfolding of MIC-1, leading to proteasomal degradation. Deletion mutagenesis showed the N-terminal 28 amino acids of the propeptide are necessary for proteasomal degradation. This is the first demonstration, to our knowledge, of a quality control function in a propeptide domain of a secretory protein and represents an additional mechanism to ensure correct folding of proteins leaving the ER.

Heteromeric assembly of GABA(B)R1 and GABA(B)R2 receptor subunits inhibits Ca(2+) current in sympathetic neurons

Neuronal GABA(B) receptors regulate calcium and potassium currents via G-protein-coupled mechanisms and play a critical role in long-term inhibition of synaptic transmission in the CNS. Recent studies have demonstrated that assembly of GABA(B) receptor GABA(B)R1 and GABA(B)R2 subunits into functional heterodimers is required for coupling to potassium channels in heterologous systems. However whether heterodimerization is required for the coupling of GABA(B) receptors to effector systems in neurons remains to be established. To address this issue, we have studied the coupling of recombinant GABA(B) receptors to endogenous Ca(2+) channels in superior cervical ganglion (SCG) neurons using nuclear microinjection to introduce both sense and antisense expression constructs. Patch-clamp recording from neurons injected with both GABA(B)R1a/1b and GABA(B)R2 cDNAs or with GABA(B)R2 alone produced marked baclofen-mediated inhibition of Ca(2+) channel currents via a pertussis toxin-sensitive mechanism. The actions of baclofen were blocked by CGP62349, a specific GABA(B) antagonist, and were voltage dependent. Interestingly, SCGs were found to express abundantly GABA(B)R1 but not GABA(B)R2 at the protein level. To determine whether heterodimerization of GABA(B)R1 and GABA(B)R2 subunits was required for Ca(2+) inhibition, the GABA(B)R2 expression construct was microinjected with a GABA(B)R1 antisense construct. This resulted in a dramatic decrease in the levels of the endogenous GABA(B)R1 protein and a marked reduction in the inhibitory effects of baclofen on Ca(2+) currents. Therefore our results suggest that in neurons heteromeric assemblies of GABA(B)R1 and GABA(B)R2 are essential to mediate GABAergic inhibition of Ca(2+) channel currents.

The P2Y(1) receptor closes the N-type Ca(2+) channel in neurones, with both adenosine triphosphates and diphosphates as potent agonists

The rat P2Y(1) nucleotide receptor, the P2Y subtype abundant in the brain, was heterologously expressed in rat superior cervical ganglion neurones by micro-injection of the receptor cRNA or cDNA. ADP inhibited the N-type Ca(2+) current by 64%, with EC(50) 8.2 nM, an action blocked competitively by the P2Y(1) receptor antagonist adenosine 3', 5'-bis-phosphate (K(i) 0.7 microM). 2-Methylthio-ADP inhibited the Ca(2+) current likewise, but with EC(50) 0.57 nM, giving the highest potency reported therewith for P2Y(1). Significantly, ATP and 2-methylthio-ATP were also agonists, the latter again at a very high potency (EC(50) 2.5 nM). We propose that this neuronal receptor, when present in brain at a high density as at synapses, can respond to very low concentrations of ATP and ADP as agonists, and that this would result in inhibition of N-type Ca(2+) currents and hence can reduce transmitter release or increase neuronal excitability.

Synapse loss associated with abnormal PrP precedes neuronal degeneration in the scrapie-infected murine hippocampus

Numbers of neurones, synapses and axon terminals were quantified in a murine scrapie model with severe hippocampal pyramidal cell loss, in which definite clinical scrapie is evident from 226 days post-infection (dpi) and death occurs around 250 dpi. Disease-specific PrP accumulations were first seen at 70 dpi (28% of the incubation period (IP)) in thalamus and as sparse foci within the stratum pyramidale of CA1. By 98 dpi (39% IP), PrP was seen in the stratum radiatum and was found at later stages throughout all levels of the hippocampus. At the ultrastructural level in the stratum radiatum of CA1, a decrease in the numbers of simple synapses from 84 dpi (34% IP) and in perforated synapses from 98 dpi (42% IP) was found using an unbiased stereological method, the disector analysis. Degeneration of axon terminals was found from 98 dpi (39% IP) onwards. Neuronal loss was detected in CA1 from 180 dpi (72% IP). The results suggest that the fundamental lesion in the hippocampus of ME7-infected mice is associated with PrP release from CA1 pyramidal neurones, which perturbs synaptic function and leads to degeneration of preterminal axons, and that subsequent pathological changes including neurone loss are sequelae to this initial insult.

Differential tetraethylammonium sensitivity of KCNQ1-4 potassium channels

In Shaker-group potassium channels the presence of a tyrosine residue, just downstream of the pore signature sequence GYG, determines sensitivity to tetraethylammonium (TEA). The KCNQ family of channels has a variety of amino acid residues in the equivalent position. We studied the effect of TEA on currents generated by KCNQ homomers and heteromers expressed in CHO cells. We used wild-type KCNQ1-4 channels and heteromeric KCNQ2/3 channels incorporating either wild-type KCNQ3 subunits or a mutated KCNQ3 in which tyrosine replaced threonine at position 323 (mutant T323Y). IC50 values were (mM): KCNQ1, 5.0; KCNQ2, 0.3; KCNQ3, > 30; KCNQ4, 3.0; KCNQ2 + KCNQ3, 3.8; and KCNQ2 + KCNQ3(T323Y), 0.5. While the high TEA sensitivity of KCNQ2 may be conferred by a tyrosine residue lacking in the other channels, the intermediate TEA sensitivity of KCNQ1 and KCNQ4 implies that other residues are also important in determining TEA block of the KCNQ channels.

Inhibition of KCNQ1-4 potassium channels expressed in mammalian cells via M1 muscarinic acetylcholine receptors

1. KCNQ1-4 potassium channels were expressed in mammalian Chinese hamster ovary (CHO) cells stably transfected with M1 muscarinic acetylcholine receptors and currents were recorded using the whole-cell perforated patch technique and cell-attached patch recording. 2. Stimulation of M1 receptors by 10 microM oxotremorine-M (Oxo-M) strongly reduced (to 0-10%) currents produced by KCNQ1-4 subunits expressed individually and also those produced by KCNQ2 + KCNQ3 and KCNQ1 + KCNE1 heteromers, which are thought to generate neuronal M-currents (IK,M) and cardiac slow delayed rectifier currents (IK,s), respectively. 3. The activity of KCNQ2 + KCNQ3, KCNQ2 and KCNQ3 channels recorded with cell-attached pipettes was strongly and reversibly reduced by Oxo-M applied to the extra-patch membrane. 4. It is concluded that M1 receptors couple to all known KCNQ subunits and that inhibition of KCNQ2 + KCNQ3 channels, like that of native M-channels, requires a diffusible second messenger.

Lipid-dependent targeting of G proteins into rafts

Domains rich in sphingolipids and cholesterol, or rafts, may organize signal transduction complexes at the plasma membrane. Raft lipids are believed to exist in a state similar to the liquid-ordered phase. It has been proposed that proteins with a high affinity for an ordered lipid environment will preferentially partition into rafts (Melkonian, K. A., Ostermeyer, A. G., Chen, J. Z., Roth, M. G., and Brown, D. A. (1999) J. Biol. Chem. 274, 3910-3917). We investigated the possibility that lipid-lipid interactions between lipid-modified proteins and raft lipids mediate targeting of proteins to these domains. G protein monomers or trimers were reconstituted in liposomes, engineered to mimic raft domains. Assay for partitioning of G proteins into rafts was based on Triton X-100 insolubility. Myristoylation and palmitoylation of Galpha(i) were necessary and sufficient for association with liposomes and partitioning into rafts. Strikingly, the amount of fatty-acylated Galpha(i) in rafts was significantly reduced when myristoylated Galpha(i) was thioacylated with cis-unsaturated fatty acids instead of saturated fatty acids such as palmitate. Prenylated betagamma subunits were excluded from rafts, whether reconstituted alone or with fatty-acylated alpha subunits. These results suggest that the structural difference between lipids that modify proteins is one basis for the selectivity of protein targeting to rafts.

Targeted mutagenesis of DNA with alkylating RecA assisted oligonucleotides

Site-specific mutation was demonstrated in a shuttle vector system using nitrogen mustard-conjugated oligodeoxyribonucleotides (ODNs). Plasmid DNA was modified in vitro by ODNs containing all four DNA bases in the presence of Escherichia coli RecA protein. Up to 50% of plasmid molecules were alkylated in the targeted region of the supF gene and mutations resulted upon replication in mammalian cells. ODNs conjugated with either two chlorambucil moieties or a novel tetrafunctional mustard caused interstrand crosslinks in the target DNA and were more mutagenic than ODNs that caused only monoadducts.

Glycosphingolipids are not essential for formation of detergent-resistant membrane rafts in melanoma cells. methyl-beta-cyclodextrin does not affect cell surface transport of a GPI-anchored protein

Recent data suggest that membrane microdomains or rafts that are rich in sphingolipids and cholesterol are important in signal transduction and membrane trafficking. Two models of raft structure have been proposed. One proposes a unique role for glycosphingolipids (GSL), suggesting that GSL-head-group interactions are essential in raft formation. The other model suggests that close packing of the long saturated acyl chains found on both GSL and sphingomyelin plays a key role and helps these lipids form liquid-ordered phase domains in the presence of cholesterol. To distinguish between these models, we compared rafts in the MEB-4 melanoma cell line and its GSL-deficient derivative, GM-95. Rafts were isolated from cell lysates as detergent-resistant membranes (DRMs). The two cell lines had very similar DRM protein profiles. The yield of DRM protein was 2-fold higher in the parental than the mutant line, possibly reflecting cytoskeletal differences. The same amount of DRM lipid was isolated from both lines, and the lipid composition was similar except for up-regulation of sphingomyelin in the mutant that compensated for the lack of GSL. DRMs from the two lines had similar fluidity as measured by fluorescence polarization of diphenylhexatriene. Methyl-beta-cyclodextrin removed cholesterol from both cell lines with the same kinetics and to the same extent, and both a raft-associated glycosyl phosphatidylinositol-anchored protein and residual cholesterol showed the same distribution between DRMs and the detergent-soluble fraction after cholesterol removal in both cell lines. Finally, a glycosyl phosphatidylinositol-anchored protein was delivered to the cell surface at similar rates in the two lines, even after cholesterol depletion with methyl-beta-cyclodextrin. We conclude that GSL are not essential for the formation of rafts and do not play a major role in determining their properties.

Speed-dependent reductions of force output in people with poststroke hemiparesis

BACKGROUND AND PURPOSE

Movement is slow in people with poststroke hemiparesis. Moving at faster speeds is thought by some researchers to exacerbate abnormal or unwanted muscle activity. The purpose of this study was to quantify the effects of increased speed on motor performance during pedaling exercise in people with poststroke hemiparesis.

SUBJECTS

Twelve elderly subjects with no known neurological impairment and 15 subjects with poststroke hemiparesis of greater than 6 months' duration were tested.

METHODS

Subjects pedaled at 12 randomly ordered workload and cadence combinations (45-, 90-, 135-, and 180-J workloads at 25, 40, and 55 rpm). Pedal reaction forces were used to calculate work done by each lower extremity. Electromyographic activity was recorded from 7 lower-extremity muscles.

RESULTS

The main finding was that net mechanical work done by the paretic lower extremity decreased as speed increased in all subjects. The occurrence of inappropriate muscle activity on the paretic side, however, was not exacerbated in that the vastus medialis muscle on the paretic side did not show a consistent further increase in its prolonged activity at higher speeds. The mechanics of faster pedaling resulted in greater net negative mechanical work because, at higher pedaling rates, the prolonged vastus medialis muscle activity is present during a greater portion of the cycle.

CONCLUSION AND DISCUSSION

The lessened force output by the paretic limb is mainly the result of the inherent mechanical demands of higher-speed pedaling and not due to exacerbation of impaired neural control.

Two types of K(+) channel subunit, Erg1 and KCNQ2/3, contribute to the M-like current in a mammalian neuronal cell

The potassium M current was originally identified in sympathetic ganglion cells, and analogous currents have been reported in some central neurons and also in some neural cell lines. It has recently been suggested that the M channel in sympathetic neurons comprises a heteromultimer of KCNQ2 and KCNQ3 (Wang et al., 1998) but it is unclear whether all other M-like currents are generated by these channels. Here we report that the M-like current previously described in NG108-15 mouse neuroblastoma x rat glioma cells has two components, "fast" and "slow", that may be differentiated kinetically and pharmacologically. We provide evidence from PCR analysis and expression studies to indicate that these two components are mediated by two distinct molecular species of K(+) channel: the fast component resembles that in sympathetic ganglia and is probably carried by KCNQ2/3 channels, whereas the slow component appears to be carried by merg1a channels. Thus, the channels generating M-like currents in different cells may be heterogeneous in molecular composition.