several treatments were based on each of these approaches.The need for reconciliation of the classification of "inert" gases in the periodic table with their demonstrated ability to form simple molecules was stressed by L. C. Allen (Princeton). He emphasized the role of instantaneous electron-electron correlations.R. J. Gillespie (McMaster University, Hamilton, Ontario) presented predictions, based on the localized electronpair theory, for molecular geometries and bond lengths of xenon oxides, fluorides, and oxyfluorides. In particular, his arguments suggest that XeFs is unlikely to be octahedrally symmetric in the vapor phase.Evidence was presented (J. Hinze and K. S. Pitzer, Rice) that unoccupied d-orbitals for the noble gas atoms are of little importance to their formation of stable compounds. The unimportance of d-orbitals and the similarity of the halogen fluorides and inert gas fluorides was emphasized by R. E. Rundle and A. J. Serewicz (Iowa State) and the reverse argued by Smith (Oak Ridge Gaseous Diffusion Plant).A comparison of six possible geometries for XeF6 (L. L. Lohr, Jr., and W. N. Lipscomb, Harvard) indicates that the octahedrally symmetric structure is the most stable form considered, as judged by semiempirical molecular orbital calculations.Finally, J. Jortner discussed absorption spectra in the near and the vacuum ultraviolet for XeF2 and XeF4 (Jortner, E. G. Wilson, and S. A. Rice, University of Chicago). He concluded that the semiempirical molecular orbital description of these compounds is in good agreement with their physical and chemical properties.The alternative prediction of symmetrical versus non-symmetrical arrangements for xenon hexafluoride deepened the apparent conflict between the alternative approaches to the formulation of chemical bonds.It is clear that additional refinement can bring either approach into agreement with the experimental observations as they are ultimately established. Nevertheless, many chemists prefer concepts that come closer to reality with fewer ad hoc adjustments.The experimental observation and the remaining uncertainty has been dis-several treatments were based on each of these approaches.The need for reconciliation of the classification of "inert" gases in the periodic table with their demonstrated ability to form simple molecules was stressed by L. C. Allen (Princeton). He emphasized the role of instantaneous electron-electron correlations.R. J. Gillespie (McMaster University, Hamilton, Ontario) presented predictions, based on the localized electronpair theory, for molecular geometries and bond lengths of xenon oxides, fluorides, and oxyfluorides. In particular, his arguments suggest that XeFs is unlikely to be octahedrally symmetric in the vapor phase.Evidence was presented (J. Hinze and K. S. Pitzer, Rice) that unoccupied d-orbitals for the noble gas atoms are of little importance to their formation of stable compounds. The unimportance of d-orbitals and the similarity of the halogen fluorides and inert gas fluorides was emphasized by R. E. Rundle a...
Cyclic AMP accumulation in rat superior cervical ganglia during synaptic activity occurs by a noncholinergic, nonadrenergic process. Both preganglionic nerve stimulation and 4-aminopyridine increase ganglion cyclic AMP levels in the presence of atropine or phentolamine. Of the polypeptides tested as putative transmitters, vasoactive intestinal polypeptide (10(-6) M) causes ganglion cyclic AMP accumulation comparable to that produced by preganglionic nerve stimulation.
Ganglionic responses to electrical stimulation, acetylcholine, and potassium ions were studied in superior cervical ganglia of. cats perfused with media containing lithium chloride instead of sodium chloride. In lithium-Locke, ganglionic transmission and depolarization evoked by acetylcholine were blocked completely but reversibly, while the depolarization produced by potassium ions was unaltered.
In the endplates of rat phrenic nervediaphragm, application of the acetylcholine-like compound, carbachol, causes a marked increase in transmitter release, as measured electrophysiologically using miniature endplate potential frequency. Washing The actions of acetylcholine (ACh) and similar compounds (cholinomimetics) on nerve membranes have been well investigated. ACh causes membrane depolarization of sensory nerve fibers, non-myelinated vagal C-fibers, sympathetic nerve fibers, and preganglionic and motor nerve endings (1-4). At adrenergic nerve terminals, ACh brings about the release of neurotransmitter (2). By contrast, application of cholinomimetics to cholinergic nerve endings has been reported to be ineffective in causing the release of transmitter from available storage sites. Electrophysiological studies at the neuromuscular junction and sympathetic ganglia have failed to detect any increase in the rate of spontaneous release of transmitter packets (miniature potentials*) in response to applied ACh or the cholinomimetic drug, carbachol (3, 4). ACh, in fact, has been shown to cause a decrease in the output of transmitter evoked by motor nerve stimulation (4, 5). Similarly, radiotracer studies at perfused sympathetic ganglia have shown that the application of carbachol apparently does not cause ACh release from transmitter storage sites, even though depolarization of the nerve terminals by K+ and nerve stimulation bring about the release of ACh into the perfusion stream (6). These findings imply that depolarization of cholinergic nerve terminals by cholinomimetics is ineffective in causing the release of ACh and that fundamental differences MATERIALS AND METHODSHemidiaphragms from young male Sprague-Dawley rats (100-130 g) were removed under ether anesthesia and mounted in a 5-ml chamber. Bath temperature was kept at 33°C by heating the perfusion fluid, gassed with 95% 02-5% C02, before entry into the chamber. A constant flow rate of 2 ml/-min was maintained using a Holter roller pump. The control solution contained: (mM) NaCl 120; KCl 5; CaCl2 2; M&C12 1; NaH2PO4 1; NaHCO3 24; glucose 17. "K+ Ringer" was made by raising KCl to 13, CaCl2 to 3, and lowering NaCl to 110 mM. The effect of elevating the concentration of K+ was an increase in basal mepp frequency (7), presumably due to nerve terminal depolarization (8). Because the frequency increase consisted of both fast and slow* components (9), diaphragms were equilibrated for at least 1 hr to ensure steadystate conditions. In the majority of cases, 500 nM tetrodotoxin was added to solutions to reduce muscle twitching and the possibility of antidromic backfiring along the motor nerve. Tetrodotoxin has been reported to have no effect on spontaneous transmitter release (10), and no differences in results were seen in the presence or absence of tetrodotoxin.Glass microelectrodes filled with 3 M KCl (15)(16)(17)(18)(19)(20) were connected to a high impedance input preamplifier. To prevent baseline drift, the output was ac-coupled to the oscilloscope...
1. Transmitter release from Mg2+‐treated frog neuromuscular junctions can be described by binomial statistics. Good agreement between the observed amplitude‐frequency distribution of e.p.p.s. and that predicted by binomial statistics is observed with relatively low concentrations of Mg2+. Conversely, good agreement is found with Poisson predictions when higher concentrations of Mg2+ are used to depress transmission. 2. Binomial analysis at these junctions shows that Mg2+ reduces quantal content (m), the probability of release (p) and to a lesser extent the available stores of transmitter (n). Raising Ca2+ causes an increase in n and p and a small but significant increase in n. K+ increases m and p but not n. 3. During 'frequency‐facilitation' (1‐6 Hz), e.p.p.s., m and n are increased but p is unaffected. 4. It is concluded that binomial statistics can be used to estimate the quantal parameters of transmitter release and that these parameters can be identified as discrete entities.
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