Radiographic comparison of grit-blasted hydroxyaptite and arc-deposited hydroxyapatite acetabular components. A four-year follow-up study.

High rates of aseptic loosening have been reported for microstructured hydroxyapatite-coated acetabular components. A macrostructured component surface (arc-deposition) not only improves resistance to shear forces experienced by the acetabular component and increases initial stability, but also provides channels for bone ingrowth. The purpose of this investigation was to radiographically compare a series of grit-blasted (microstructured) and arc-deposited (macrostructured) hydroxyapatite-coated acetabular components. A minimum 4-year retrospective radiographic analysis of acetabular components was performed on a total of 50 total hip arthroplasties. At 4 years, arc-deposited components were associated with fewer radiolucent lines in all Charnley zones, particularly Charnley zone III. While the 4-year results for arc-deposited hydroxyapatite acetabular components are superior to their microstructured predecessors, long-term results are still unknown.

Zinc elevates neuropeptide Y levels in rat pheochromocytoma cells by a mechanism independent of L-channel mediated inhibition of release.

Both zinc and neuropeptide Y (NPY) have been implicated as playing a role in seizures and feeding behavior. We investigated the hypothesis that zinc could regulate levels of NPY, and found that chronic exposure to 50-100 microM zinc increased levels of cellular NPY in cultured PC12 cells grown in the presence of nerve growth factor. Zinc's effect on NPY was specific, time- and concentration-dependent, and independent of inhibition of NPY release secondary to blockade of dihydropyridine-sensitive calcium channels. These results are consistent with a role for zinc in regulating hippocampal NPY following high-frequency neuronal activity.

Subtrochanteric femoral shortening osteotomy in total hip arthroplasty for high-riding developmental dislocation of the hip.

A surgical technique, which uses a transverse osteotomy, for subtrochanteric femoral shortening and derotation in total hip arthroplasty for high-riding developmental dislocation of the hip is described. Anteversion is set by rotating the osteotomy fragments, and torsional stability is augmented with allograft struts and cables when indicated. Eight patients with 9 total hip arthroplasties were followed for an average of 43 months (range, 24-84 months). Good to excellent results were obtained in 87% of patients (7 of 8). Eight of 9 osteotomies (89%) demonstrated radiographic evidence of healing at an average of 5 months. One patient had an asymptomatic nonunion of the osteotomy site but still had a good overall clinical result. Another patient suffered fatigue failure of a distally ingrown porous device, which necessitated revision total hip arthroplasty 18 months after surgery. Subtrochanteric osteotomy in total hip arthroplasty for developmental dislocation of the hip allows for acetabular exposure and diaphyseal shortening while facilitating femoral derotation. Furthermore, proximal femoral bone stock is maintained and some of the potential complications of greater trochanteric osteotomy may be avoided.

Calcium regulation of vasoactive intestinal polypeptide mRNA abundance in SH-SY5Y human neuroblastoma cells.

Second messenger regulation of gene expression provides a mechanism by which neurons can transduce environmental stimuli into long-term changes in the expression of molecules involved in neuronal signaling. We have investigated calcium-dependent induction of vasoactive intestinal polypeptide (VIP) mRNA and compared it with induction of VIP mRNA by cyclic AMP. Depolarization with 60 mM KCl or exposure to the calcium ionophore A23187 increases VIP mRNA levels in SH-SY5Y cells. The increase in VIP mRNA content in response to Ca2+ mobilization is slow, independent of adenylate cyclase activation, and requires de novo protein synthesis. The increase in VIP mRNA content in response to elevation of cyclic AMP levels by forskolin/isobutylmethylxanthine is independent of Ca2+ influx and does not require new protein synthesis. The mRNA for the transcription factors ATF-3, c-fos, c-jun, junB, and zif/268 is induced by A23187. Of these, ATF-3 showed the greatest relative induction by A23187 compared with induction by forskolin/isobutylmethylxanthine.

Calcium channels and calcium-gated potassium channels at the frog neuromuscular junction.

Two mechanisms which regulate transmitter release by regulating Ca2+ entry in the presynaptic nerve terminal were studied at the frog neuromuscular junction (nmj). First, the location of Ca2+ channels in relation to transmitter release sites and, second, the regulation of Ca2+ entry by Ca(2+)-gated potassium (gKca) channels. Ca2+ channels were disclosed using fluorescent omega-conotoxin GVIA (omega-CgTX) which blocks transmitter release and Ca2+ entry at the frog nmj. Ca2+ channels were located in bands spaced at regular intervals of 1 micron. The omega-CgTX labeling was removed following mechanical displacement of the presynaptic terminal after collagenase digestion. The bands of omega-CgTX staining matched almost perfectly the staining of cholinergic receptors with fluorescent alpha-bungarotoxin (alpha-BuTX) and therefore must be located at the active zone. The role of gKca channels in the regulation of transmitter release was assessed using charybdotoxin (ChTX) which blocks gKca channels of large and intermediate conductances. Application of ChTX (2-20 nM) induced a two-fold increase in transmitter release which was prevented when a membrane permeant Ca2+ buffer (DMBAPTA-AM) was introduced prior to the toxin application. The Ca2+ buffer by itself caused a reduction in transmitter release. Nerve-evoked Ca2+ entry in the presynaptic terminal, detected with the fluorescent indicator fluo3, was increased following gKca channel blockade by ChTX. The Ca(2+)-gated K+ channels may function to limit the duration of the presynaptic action potential and thus limit Ca2+ entry.

Molecular cloning of the rat A2 adenosine receptor: selective co-expression with D2 dopamine receptors in rat striatum.

A cDNA fragment homologous to other G protein-coupled receptors was isolated from rat brain using the PCR method and demonstrated to be abundantly expressed in striatum. Using this fragment as a probe, a 2.1 kb full-length cDNA was isolated from a rat striatal cDNA library. This cDNA encodes a protein of 410 amino acids and is highly homologous to previously isolated adenosine receptor cDNAs. Expression of this cDNA in COS cells revealed high affinity (Kd = 38.6 nM) and saturable binding of the A2 adenosine receptor-selective ligand [3H]CGS 21680. Agonist displacement profile of [3H]CGS 21680 binding was consistent with an adenosine receptor of the A2 subtype (NECA greater than (R)-PIA greater than CPA greater than (S)-PIA). In situ hybridization demonstrated that rat A2 adenosine receptor mRNA was co-expressed in the same striatal neurons as D2 dopamine receptor mRNA, and never co-expressed with striatal D1 dopamine receptor mRNA. Several lines of evidence have previously suggested that dopamine-induced changes in motor behavior can be modulated by adenosine analogs acting at the A2 subtype of adenosine receptor in the forebrain. The co-expression of D2 dopamine and A2 adenosine receptors in a subset of striatal cells provides an anatomical basis for dopaminergic-adenosinergic interactions on motor behavior.

Presynaptic calcium signals during neurotransmitter release: detection with fluorescent indicators and other calcium chelators.

Synthetic calcium buffers, including fluorescent calcium indicators, were microinjected into squid 'giant' presynaptic nerve terminals to investigate the calcium signal that triggers neurotransmitter secretion. Digital imaging methods, applied in conjunction with the fluorescent calcium indicator dye fura-2, reveal that transient rises in presynaptic calcium concentration are associated with action potentials. Transmitter release terminates within 1-2 ms after a train of action potentials, even though presynaptic calcium concentration remains at micromolar levels for many seconds longer. Microinjection of the calcium buffer, EGTA, into the presynaptic terminal has no effect on transmitter release evoked by single presynaptic action potentials. EGTA injection does, however, block the change in calcium concentration measured by fura-2. Therefore, the calcium signal measured by fura-2 is not responsible for triggering release. These results suggest that the rise in presynaptic calcium concentration that triggers release must be highly localized to escape detection with fura-2 imaging. Unlike EGTA, microinjection of BAPTA--a calcium buffer with an equilibrium affinity for calcium similar to that of EGTA--produces a potent, dose-dependent, and reversible block of action-potential evoked transmitter release. The superior ability of BAPTA to block transmitter release apparently is due to the more rapid calcium-binding kinetics of BAPTA compared to EGTA. Because EGTA should bind calcium within a few tens of microseconds under the conditions of our experiments, the inability of EGTA to block release indicates that transmitter release is triggered within a few tens of microseconds after the entry of calcium into the presynaptic terminal.(ABSTRACT TRUNCATED AT 250 WORDS)

Alien intracellular calcium chelators attenuate neurotransmitter release at the squid giant synapse.

A number of calcium buffers were examined for their ability to reduce evoked transmitter release when injected into the presynaptic terminal of the squid giant synapse. Injection of EGTA was virtually ineffective at reducing transmitter release, even at estimated intracellular concentrations up to 80 mM. Conversely, the buffer 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), which has an equilibrium affinity for calcium similar to that of EGTA at pH 7.2, produced a substantial reduction in transmitter release when injected presynaptically. This effect of BAPTA was reversible, presumably because the buffer diffused out of the terminal and into uninjected regions of the presynaptic axon. BAPTA derivatives with estimated intracellular calcium dissociation constants (Kd) ranging from 0.18 to 4.9 microM were effective at reducing transmitter release at similar estimated concentrations. A BAPTA derivative with an estimated intracellular Kd of 31 mM was less effective. BAPTA did not affect presynaptic action potentials or calcium spikes in ways that could explain its ability to reduce transmitter release. The relative effects of presynaptic injections of BAPTA and derivatives are consistent with the calcium-buffering capability of these compounds if the presynaptic calcium transient that triggers release is hundreds of microM or larger. The superior potency of BAPTA compared to EGTA apparently results from the faster calcium-binding kinetics of BAPTA and suggests that the calcium-binding molecule that triggers release binds calcium in considerably less than 200 microsec and is located very close to calcium channels.

Strategic location of calcium channels at transmitter release sites of frog neuromuscular synapses.

The localization of Ca2+ channels relative to the position of transmitter release sites was investigated at the frog neuromuscular junction (NMJ). Ca2+ channels were labeled with fluorescently tagged omega-conotoxin GVIA, an irreversible Ca2+ channel ligand, and observed with a confocal laser scanning microscope. The Ca2+ channel labeling almost perfectly matched that of acetylcholine receptors which were labeled with fluorescent alpha-bung-arotoxin. This indicates that groups of Ca2+ channels are localized exclusively at the active zones of the frog NMJ. Cross sections of NMJs showed that Ca2+ channels are clustered on the presynaptic membrane adjacent to the postsynaptic membrane.

Frequency-dependent action of phenytoin on lamprey spinal axons.

The effect of the antiepileptic drug phenytoin (diphenylhydantoin, DPH) was tested on the conduction of intracellularly recorded action potentials in lamprey giant reticulospinal axons. When the isolated spinal cord was exposed to 80 microM DPH for up to 4 h, no significant effect was seen on the amplitude or conduction velocity of the action potential, although the maximum rate of rise was reduced from 247.8 to 149.6 V/s after 1 h. However, at higher stimulus frequencies both the amplitude and conduction velocity of the action potential were reduced progressively during a 500 stimulus train. The reduction was greater the higher the stimulus frequency, and was reversed upon return to 1 Hz stimulation. At frequencies greater than 40 Hz an all-or-none block developed. This also developed sooner the higher the stimulus frequency. Axons bathed in drug-free solutions did not show this effect at stimulus frequencies up to 100 Hz. Similar effects were seen in 16 microM DPH when the spinal cord was exposed to the drug overnight. This is close to the human therapeutic CSF level. The frequency-dependent depression of the action potential was greatly potentiated by increasing the extracellular potassium concentration from 2.1 to 5 mM. Under these conditions the axons rapidly developed block at stimulus frequencies as low as 2 Hz, and this was not reversible during a 5 h wash. In the absence of DPH, 5 mM potassium produced a 4-5 mV depolarization, but did not induce a frequency-dependent block. This effect of potassium may be important to the therapeutic effect of DPH because during epileptiform activity the extracellular K+ increases several fold.

Anomalous patterns in cultured cell monolayers.

Gridlike patterns of differing cell density were observed in evenly seeded cell monolayers. Such patterns were obtained in five of six cell lines tested, suggesting widespread occurrence. The mechanism appears to involve small, transient temperature changes related to incubator tray structure. The very short time course of appearance of the patterns implicates attachment rather than growth as the critically affected factor. Impaired adhesion or directed sedimentation resulting from thermally induced microcurrents in the medium are the two most likely mechanisms.