Immunocytochemical localization of 155 kDa myosin light chain kinase and myosin heavy chain in bovine brain

Multiple pathways of sigma(1) receptor ligand uptakes into primary cultured neuronal cells

Although many antipsychotics have affinities for sigma receptors, the transportation pathway of exogenous sigma(1) receptor ligands to intracellular type-1 sigma receptors are not fully understood. In this study, sigma(1) receptor ligand uptakes were studied using primary cultured neuronal cells. [(3)H](+)-pentazocine and [(3)H](R)-(+)-1-(4-chlorophenyl)-3-[4-(2-methoxyethyl)piperazin-1-yl]methyl-2-pyrrolidinone L-tartrate (MS-377), used as a selective sigma(1) receptor ligands, were taken up in a time-, energy- and temperature-dependent manner, suggesting that active transport mechanisms were involved in their uptakes. sigma(1) receptor ligands taken up into primary cultured neuronal cells were not restricted to agonists, but also concerned antagonists. The uptakes of these ligands were mainly Na(+)-independent. Kinetic analysis of [(3)H](+)-pentazocine and [(3)H]MS-377 uptake showed K(m) values (microM) of 0.27 and 0.32, and V(max) values (pmol/mg protein/min) of 17.4 and 9.4, respectively. Although both ligands were incorporated, the pharmacological properties of these two ligands were different. Uptake of [(3)H](+)-pentazocine was inhibited in the range 0.4-7.1 microM by all the sigma(1) receptor ligands used, including N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100), a selective sigma(1) receptor ligand. In contrast, the inhibition of [(3)H]MS-377 uptake was potently inhibited by haloperidol, characterized by supersensitivity (IC(50), approximately 2 nM) and was inhibited by NE-100 with low sensitivity (IC(50), 4.5 microM). Moreover, kinetic analysis revealed that NE-100 inhibited [(3)H]MS-377 uptake in a noncompetitive manner, suggesting that NE-100 acted at a site different from the uptake sites of [(3)H]MS-377. These findings suggest that there are at least two uptake pathways for sigma(1) receptor ligands in primary cultured neuronal cells (i.e. a haloperidol-sensitive pathway and another, unclear, pathway). In addition, pretreatment of cells with a calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7), a myosin light chain kinase inhibitor, 1-(5-chloronaphthalene-1-sulfonyl)homopiperazine (ML-9), or microsomal Ca(2+)-ATPase inhibitors resulted in a reduction of the amount of sigma receptor ligand uptake. These findings suggest that the Ca(2+) pump on the endoplasmic reticulum and/or calmodulin-related events might be involved in the regulation of the uptake of sigma receptor ligands into primary neuronal cells.

Non-muscle myosin IIB-like immunoreactivity is present at the drebrin-binding cytoskeleton in neurons

Dendritic spines are extremely motile, providing a structural mechanism for synaptic plasticity. Actin-myosin interaction is thought to be responsible for the change in the shape of spine. We have already reported that drebrin, an actin-binding protein, inhibits actin-myosin interaction and is enriched in the dendritic spine of mature neurons. In this study, we prepared the actin cytoskeleton of dendritic spines as an immunoprecipitate with anti-drebrin antibody from adult guinea-pig brain, immunized mice with the cytoskeleton, and obtained a monoclonal antibody (MAb) called MAb G650. MAb G650 reacted with non-muscle myosin IIB, but it did not react with muscle myosin II or non-muscle myosin IIA. Immunoblotting with this antibody revealed that drebrin-binding cytoskeleton contains this myosin IIB-like immunreactivity. Immunohistochemistry using MAb G650 demonstrated that this myosin IIB-like immunreactivity can be detected in the neuronal cell bodies and their apical dendrites, where drebrin is hardly detected. These data demonstrate that a myosin subtype associated with drebrin-binding actin filaments in the dendritic spines is myosin IIB, although this myosin is widely distributed in somato-dendritic subdomains of neurons. Furthermore, it is indicated that the cytoskeletons in dendritic spine were uniquely characterized with actin-binding proteins such as drebrin, but not with myosins.

Redifferentiation of smooth muscle cells after coronary angioplasty determined via myosin heavy chain expression

BACKGROUND

The pathophysiology of phenotypic modulation of smooth muscle cells (SMCs) involved in restenosis after angioplasty is not well understood. Smooth muscle myosin heavy chain (SM MHC) isoforms (SM1 and SM2) are specific markers for SMC differentiation. In particular, SM2 is useful as a marker of mature SMCs. SMemb is a nonmuscle myosin heavy chain (NM MHC) whose expression is upregulated in immature or activated SMC.

METHODS AND RESULTS

To determine SMC phenotypes in neointimal tissues after percutaneous transluminal coronary angioplasty (PTCA), we performed immunohistochemistry on human coronary arteries with antibodies against alpha-SM actin, SM1, SM2, and SMemb. Tissues were obtained from six autopsied patients and from atherectomy specimens from 16 patients who had undergone PTCA. Medial SMCs were positive for alpha-actin, SM1, and SM2. Expression of SM1 and SM2 in the neointima varied with the time after intervention, whereas alpha-actin was constitutively expressed in all cases studied. Neointimal cells at 16 and 20 days after PTCA contained alpha-actin but little or no SM1 or SM2, indicating that these cells modulated their phenotype to the immature state. Neointimal SMCs recovered SM MHC expression, first SM1 and then SM2, by 6 months after PTCA. Increased expression of SMemb was found in the neointima but without apparent relationship to the time after PTCA.

CONCLUSIONS

Neointimal SMCs show features of an undifferentiated state, indicated by altered expression of SM MHC, and undergo redifferentiation in a time-dependent manner. The expression of SM MHC isoforms provides insight into the biology of healing after angioplasty and furnishes useful tools for the understanding of the roles of differentiation and phenotypic modulation of SMCs in human vascular lesions.