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R K Yip

Publications and source records attributed to R K Yip.

9 recordsLinked to original sources
PubMed1992

Immunologic identification of Na/Ca exchange protein in rat brain synaptic plasma membrane.

Polyclonal antibodies raised against partially purified dog cardiac Na/Ca exchanger react with cardiac sarcolemmal proteins of 160, 120 and 70 kDa on SDS-PAGE. Using the same specific antiserum, we detected three prominent immunoreactive bands of about 150, 120 and 70 kDa on immunoblots with rat forebrain synaptic plasma membrane proteins. These data indicate that the Na/Ca exchange protein in rat brain synaptic plasma membrane is structurally and antigenically similar to the exchange protein in dog cardiac sarcolemma.

Animals↗
PubMed1992

Presynaptic localization of sodium/calcium exchangers in neuromuscular preparations.

Calcium ions play a critical role in neurotransmitter release. The cytosolic Ca2+ concentration ([Ca2+]cyt) at nerve terminals must therefore be carefully controlled. Several different mechanisms, including a plasmalemmal Na/Ca exchanger, are involved in regulating [Ca2+]cyt. We employed immunofluorescence microscopy with polyclonal antiserum raised against dog cardiac sarcolemmal Na/Ca exchanger to determine the distribution of the exchanger in vertebrate neuromuscular preparations. Our data indicate that the Na/Ca exchanger is concentrated at the neuromuscular junctions of the rat diaphragm. The exchanger is also present in the nonjunctional sarcolemma, but at a much lower concentration than in the junctional regions. Denervation markedly lowers the concentration of the exchanger in the junctional regions; this implies that the Na/Ca exchanger is concentrated in the presynaptic nerve terminals. In Xenopus laevis nerve and muscle cell cocultures, high concentrations of the exchanger are observed along the neurites as well as at the nerve terminals. The high concentrations of Na/Ca exchanger at presynaptic nerve terminals in vertebrate neuromuscular preparations suggest that the exchanger may participate in the Ca-dependent regulation of neurotransmitter release. The Na/Ca exchanger is also abundant in developing neurites and growth cones, where it may also be important for Ca2+ homeostasis.

Animals↗
PubMed1989

In situ protein phosphorylation in hippocampal tissue slices.

We have studied the subcellular distribution of phosphoproteins in intact hippocampal slices and examined factors that regulate their phosphorylation and dephosphorylation in situ. The presence of Ca2+ in slice equilibration and prelabeling buffers and high-K+-induced depolarization markedly increased 32Pi incorporation into endogenous proteins. Ca2+-stimulatory effects were significantly reduced by Ca2+-channel blockers and the calmodulin antagonist W-13. Certain proteins were dephosphorylated in situ, and their dephosphorylation was dependent on both Ca2+ and depolarization. A number of proteins phosphorylated in situ was similar to those previously characterized in synaptic fractions phosphorylated in vitro. Many phosphoproteins were identified on the basis of molecular weight, isoelectric point, immunoreactivity, and phosphopeptide mapping; these included the 87 kDa substrate of protein kinase C, synapsin I, the 50 and 60 kDa subunits of Ca2+/calmodulin-dependent protein kinase II (CKII), tubulin, B-50, the alpha-subunit of pyruvate dehydrogenase and myelin basic proteins. CKII phosphorylation in situ appeared similar but not identical to its in vitro counterpart. Phosphopeptide mapping analysis of in situ labeled substrate proteins indicated that cAMP-, Ca2+/calmodulin-, and Ca2+/phospholipid-dependent protein kinases were all active in slice preparations under basal conditions. Increased 32Pi labeling of hippocampal proteins following tissue depolarization appeared to be associated with increased activity of endogenous protein kinases since depolarization did not result in 32Pi-labeling of any new phosphoproteins.

Animals↗
PubMed1987

Effects of methylmercury on the motor and sensory innervation of the rat extensor digitorum longus muscle.

This histochemical study examined the effects of chronic methylmercury (MeHg) intoxication on the motor and sensory innervation of extensor digitorum longus muscles. Light microscopic examination of silver-stained axons in the intramuscular nerve bundles of MeHg-treated rats showed Wallerian-like degeneration and a reduction in the number of nerve fibers. Disrupted axons were predominantly sensory because 22.2% of spindle afferents (Ia) and 90.0% of Golgi tendon organ (Ib) sensory fibers were completely degenerated whereas less than 1% of motor endings were totally destroyed. Partial disruption occurred in the cholinesterase and motor terminals of 13.7% of endplates. Our results demonstrated greater vulnerability of sensory nerves than of motor nerves to MeHg-induced degeneration. Thus, the abnormal reflexes, ataxia, and muscle weakness following MeHg poisoning appear related to reduction of proprioceptive feedback from muscles and tendons in addition to the documented lesions in the central nervous system.

Animals↗
PubMed1985

Calmodulin-dependent protein phosphorylation in synaptic junctions.

Synaptic junctions (SJs) from rat forebrain were examined for Ca2+/calmodulin (CaM)-dependent kinase activity and compared to synaptic plasma membrane (SPM) and postsynaptic density (PSD) fractions. The kinase activity in synaptic fractions was examined for its capacity to phosphorylate endogenous proteins or exogenous synapsin I, in the presence or absence of Ca2+ plus CaM. When assayed for endogenous protein phosphorylation, SJs contained approximately 25-fold greater amounts of Ca2+/CAM-dependent kinase activity than SPMs, and fivefold more activity than PSDs. When kinase activities were measured by phosphorylation of exogenous synapsin I, SJs contained fourfold more activity than SPMs, and 10-fold more than PSDs. The phosphorylation of SJ proteins of 60- and 50-kilodalton (major PSD protein) polypeptides were greatly stimulated by Ca2+/CaM; levels of phosphorylation for these proteins were 23- and 17-fold greater than basal levels, respectively. Six additional proteins whose phosphorylation was stimulated 6-15-fold by Ca2+/CAM were identified in SJs. These proteins include synapsin I, and proteins of 240, 207, 170, 140, and 54 kilodaltons. The 54-kilodalton protein is a highly phosphorylated form of the major PSD protein and the 170-kilodalton component is a cell-surface glycoprotein of the postsynaptic membrane that binds concanavalin A. The CaM-dependent kinase in SJ fractions phosphorylated endogenous phosphoproteins at serine and/or threonine residues. Ca2+-dependent phosphorylation in SJ fractions was strictly dependent on exogenous CaM, even though SJs contained substantial amounts of endogenous CaM (15 micrograms CaM/mg SJ protein). Exogenous CaM, after being functionally incorporated into SJs, was rapidly removed by sequential washings. These observations suggest that the SJ-associated CaM involved in regulating Ca2+-dependent protein phosphorylation may be in dynamic equilibrium with the cytoplasm. These findings indicate that a brain CaM-dependent kinase(s) and substrate proteins are concentrated at SJs and that CaM-dependent protein phosphorylation may play an important role in mechanisms that underlie synaptic communication.

Amino Acids↗
PubMed1983

Corn oil-induced changes in the dorsal root ganglia of rats.

The effects of corn oil on rat dorsal root ganglia (DRG) were examined by both light and electron microscopy. Rats were fed corn oil via intubation 5 days per week for 7 weeks. No apparent morphological lesion was observed in the DRG by means of light microscopic examination. However, various cytological changes were revealed by electron microscopy. The most prominent change was the extensive and severe edematous condition in the interstitial space. After 7 weeks of treatment, the interstitial space between neurons and nerve fibers was distended by proteinaceous edematous fluid and collagen fibers. Distention of the intercellular space between the ganglion neurons and their surrounding satellite cell sheaths also occurred. Proliferation of the supporting cells, especially the satellite cells and Schwann cells, producing long and complex networks of cellular processes in the distended interstitial space was also evident. It is believed that chronic ingestion of corn oil by rats has an adverse effect on the endothelial system leading to an increased fluid permeability and edematous condition.

Animals↗