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C A Lindgren

Publications and source records attributed to C A Lindgren.

8 recordsLinked to original sources
PubMed1997

Intracellular acidification reversibly reduces endocytosis at the neuromuscular junction.

The close spatial and temporal coupling of endocytosis and exocytosis in nerve terminals has made it difficult to elucidate the mechanisms and the regulation of endocytosis per se. Despite significant advances in our knowledge of the molecules involved in endocytosis, it has not yet been possible to selectively manipulate endocytosis in nerve terminals. We report that the substitution of propionate for chloride in the saline bathing a lizard neuromuscular junction reduces internal pH and reversibly blocks activity-dependent endocytosis. When intraterminal pH is reduced by approximately 0.7 pH units, the uptake of FM1-43 in nerve terminals, but not activity-dependent destaining, is reduced. Normalization of intracellular pH by removing the propionate, raising extracellular pH, or adding ammonium chloride immediately restores FM1-43 uptake. Electron microscopy indicates that intracellular acidification reversibly reduces activity-dependent endocytosis in nerve terminals, because depolarization in propionate saline leads to a depletion of vesicles and the appearance of large intramembraneous infoldings.

Animals↗
PubMed1994

Nitroprusside inhibits neurotransmitter release at the frog neuromuscular junction.

Sodium nitroprusside (SNP), when applied at concentrations ranging from 0.01 microM to 1.0 mM, reduced endplate potentials in sartorius muscle fibers of the frog (Rana pipiens) by a mean of 57% (range 37-79%). Using quantal analysis, this reduction was shown to be predominantly, if not exclusively, due to a reduction in neurotransmitter release rather than a decrease in postsynaptic sensitivity. Inhibition of neuromuscular transmission was not observed if the preparation was pretreated with bovine hemoglobin prior to the addition SNP nor if 'old' SNP solutions, in which the SNP had decomposed for at least 24 h, were applied. These results suggest that nitric oxide inhibits the evoked release of neurotransmitter at the frog neuromuscular junction.

Animals↗
PubMed1989

Identification of ionic currents at presynaptic nerve endings of the lizard.

1. Ionic currents associated with the invasion of an action potential into the motor nerve ending of the lizard, Anolis carolinensis, were measured with a focal extracellular electrode at several locations along the nerve ending. 2. These experimentally observed currents could be matched with computer simulations of action potential propagation into the nerve ending. They revealed that while Na+ channels are the major ionic current pathway in the heminode, K+ channels provide the major pathway in the terminal branches and boutons. 3. Calcium current in the presynaptic ending was unmasked by the application of tetraethylammonium (TEA). This current was blocked by: (a) cadmium, (b) omega-conotoxin GVIA and (c) nifedipine, but was unaffected by nickel at concentrations less than or equal to 100 microM. Nifedipine's action became more definitive when the duration of the action potential was greatly extended by pre-treatment with TEA. The effect of Bay K 8644 was inconsistent. 4. Transmitter release, as measured by postsynaptic current, had a pharmacological response profile similar to that of the Ca2+ current, with the exception that transmitter release was increased reliably and reversibly by Bay K 8644. 5. This pharmacological response profile is identical to that of the L type Ca2+ channel identified by Fox, Nowycky & Tsien (1987 alpha) in chick dorsal root ganglion neurones. We saw no evidence for more than a single type of Ca2+ channel in lizard motor nerve endings. 6. A calcium-activated K+ current IK(Ca) was revealed by application of 3,4-diaminopyridine (DAP), a delayed-rectifier K+ channel blocker. This K(Ca) current was blocked by TEA, charybdotoxin and by substitution of cobalt for extracellular calcium.

Animals↗
PubMed1987

Extracellular ATP modulates calcium uptake and transmitter release at the neuromuscular junction.

Adenosine, AMP, ADP, and ATP were tested for their ability to modulate evoked quantal transmitter release at excitor-opener nerve terminals in the crayfish walking leg. Only ATP was found to have a significant effect, inhibiting release by 43%. To determine whether the effects of extracellular ATP on transmitter release were related to changes in free Ca2+ levels in the nerve terminal, net 45Ca uptake was measured in regions of the nerve near the terminal; although resting 45Ca uptake was increased by 5 mM exogenous ATP. Thus, extracellular ATP normally inhibits evoked transmitter release; this is associated with reduced stimulation-induced net Ca2+ uptake into the synaptic terminal. To explore the possibility that metabolic factors might be involved, nerve ATP levels were reduced by greater than or equal to 50% by omitting glucose from the bathing solution. Although quantal content and synaptic delay were unaffected by reduced intracellular ATP, under these conditions 5 mM exogenous ATP failed to reduce quantal release. Five millimolars of ATP did increase synaptic facilitation, however, which is consistent with a reduced ability to regulate intracellular free Ca2+. Therefore, under conditions of reduced intracellular ATP, the increased resting Ca2+ uptake produced by 5 mM ATP is not buffered completely. This leads to elevated free Ca2+ levels in the nerve terminal, increasing the amount of transmitter released following an action potential.

Acetylcholine↗
PubMed1986

Increased presynaptic ATP levels coupled to synaptic activity at the crayfish neuromuscular junction.

Levels of ATP and related adenylates were measured in the terminal region of efferent nerves in the crayfish opener muscle using the luciferin-luciferase method. Following 1 min of stimulation at 50 Hz, the average (+/- SE) ATP content rose from 13.4 (+/- 1.5) to 19.0 (+/- 2.1) nmol/mg dry weight. The amounts of ADP, AMP, and the phosphagen phosphoarginine did not change significantly. Thus, the increased ATP was not derived from any of these potential sources. The increase was found to depend on synaptic activation, however, for its magnitude was directly related to the concentration of extracellular Ca2+, and it was blocked when CoCl2, verapamil, ruthenium red, or gamma-methylglutamate and picrotoxin were added to the bath. Addition of ATP to the bath solution also increased nerve ATP levels. Based upon measurements of sucrose distribution, only 50% of this increase was in the extracellular water space. The remainder of the ATP had either entered the nerve, become adsorbed extracellularly, or both. Addition of 2-deoxy-D-glucose and gamma-32P-ATP to the bath resulted in the formation of 32P-2-deoxy-D-glucose-6-P by the nerve. This suggests that a fraction of the extracellular ATP does enter the neuron chemically intact. To determine whether exogenous ATP is the source of the increased ATP measured in the nerve following stimulation, the bath was assayed for ATP. Stimulation did cause ATP levels to increase significantly; however, the maximum concentration was 3 orders of magnitude lower than that required to increase ATP levels in resting nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1982

Isolated cardiac myocytes. A new cellular model for studying insulin modulation of monosaccharide transport.

The usefulness of isolated Ca2+-tolerant myocytes as a cellular model system for investigating modulation of monosaccharide transport by insulin was investigated. We have found that the isolation technique described by Haworth et al. (Haworth, R.A., Hunter, D.R. and Berkoff, H.A. (1980) J. Mol. Cell. Cardiol. 12, 715-724), with some minor modifications, consistently gave the highest yield of quiescent, rod-shaped myocytes which maintained their integrity in the presence of 2 mM calcium. Using 3-0-methylglucose, a non-metabolized sugar, transport was shown to possess saturability, substrate stereospecificity, competition and countertransport; all of which have been thoroughly established for D-glucose transport in other systems. The apparent Km of transport ranged from 2.3 to 3.5 mM. Insulin (10 nM) caused a small but significant increase in Km and a 2-3-fold increase in Vmax. These results suggest that this myocyte preparation will provide a useful model for studying the transport-related effects of insulin as well as current hypotheses regarding the mechanism of insulin modulation of transport at the cellular level.

3-O-Methylglucose↗