Roles of Calcium Ions and Cyclic AMP in Olfactory Transduction

The roles of Ca2 + and cAMP in olfactory transduction were explored using agents which affect calcium channels and second messenger systems. These agents were applied at certain calculated final concentrations onto olfactory epithelia of urethane-anesthetized frogs (Sana PiPlens) by two-sec aerosol spray. During extracellular recording, saturated vapors of isoamyl acetate were delivered every 100 sec in 0.3 sec pulses to produce an electroolfactogram (EOG). Inorganic cations that block inward calcium currents inhibit EOG responses with the following rank order: (La3+) > (Zn2+, Cd2+) > (Al3+, Ca2+, Sr2+) > (Co2+). Application of 7.5 mM La3+ eradicates £0G's, while Ba2+ (which can carry more current that Ca2+) initially produces significant enhancement (F=43.04, p<0.001, df=19). Magnesium ion has no effect on EOG's at 7.5 mM, while 1.5 X 10"4M Ca2+ is significantly inhibitory (F=5.74; p=0.0355; df=12). Control aerosol sprays of distilled water depress EOG's by an average of 5%. The organic calcium channel antagonists diltiazem and verapamil inhibit EOG's by 17% and 36X, respectively, at a concentration of 1.5 X 10~*M. Verapamil produces significant inhibition (F=17.17; p=0.002; df=ll) at 1.5 X 10" 5 M, while the 1,4-dihydropyridine calcium channel antagonists, nicardipine and nifedipine, do not inhibit beyond 1% DMSO controls. Several calmodulin antagonists decrease EOG's, but without correlation to their anti-calmodulin potency. Application of 1.5 X 10"*M chlorpromazine and N-(6-aminohexyl)-5-chloro-l-naphthalenesulfonamide inhibit EOG's by 31% and 27%, respectively, while trifluoperazine inhibits by 23%. Dibutyryl cAMP, a lipophilic mimic of cAMP, produces 54% inhibition at 1.5 X 10" *M. Dibutyryl cGMP, cGMP, cAMP, and adenosine all decrease EOG's by less than 15% compared to distilled water controls. Forskolin, a reversible activator of adenylate cyclase, inhibits EOG's by 57% at 1.5 X 10"5M, which is significant beyond the 1% DMSO controls (F=17.17; p=0.002; df=ll). These data support the hypothesis that Ca2+ participates in olfactory transduction. Calcium ions could serve as charge carriers, second messengers, or both. Cyclic AMP could be involved with the primary excitatory process or sensory adaptation, or both

Isoflurane depresses hippocampal CA1 glutamate nerve terminals without inhibiting fiber volleys-2

<p><b>Copyright information:</b></p><p>Taken from "Isoflurane depresses hippocampal CA1 glutamate nerve terminals without inhibiting fiber volleys"</p><p>BMC Neuroscience 2006;7():5-5.</p><p>Published online 12 Jan 2006</p><p>PMCID:PMC1369004.</p><p>Copyright © 2006 Winegar and MacIver; licensee BioMed Central Ltd.</p>SP depression under each condition were almost identical. The actions of these treatments are shown for EPSP depression (), FV-EPSP curve slopes (I/O slopes; ) and paired-pulse facilitation (PPF; ). Each bar represents the mean ± standard deviation for at least five experiments from different slice preparations. Note that each treatment substantially depressed EPSPs but only isoflurane and low Caproduced a significant change in the I/O slope compared to TTX (p < 0.001 in both cases, ANOVA). PPF with isoflurane and low Cawas also significantly greater than with TTX (p < 0.001 and p < 0.001 respectively, ANOVA)

Isoflurane depresses hippocampal CA1 glutamate nerve terminals without inhibiting fiber volleys-0

<p><b>Copyright information:</b></p><p>Taken from "Isoflurane depresses hippocampal CA1 glutamate nerve terminals without inhibiting fiber volleys"</p><p>BMC Neuroscience 2006;7():5-5.</p><p>Published online 12 Jan 2006</p><p>PMCID:PMC1369004.</p><p>Copyright © 2006 Winegar and MacIver; licensee BioMed Central Ltd.</p> measurement: a minimum-to-baseline (MTB) algorithm was used to measure FV and EPSP amplitudes (dashed lines); a (slope) algorithm was used to measure the initial slope of FVs (1) and EPSPs (2). , () comparison of slope and amplitude measures of FVs as a function of stimulus voltage. Open circles are FV amplitudes measured by MTB (r= 0.99; n = 60). Green circles are FV slope measurements that were scaled to match the amplitude data (r= 0.85; n = 60). Each data set was fit by linear regression (solid lines). , () comparison of slope and amplitude measures of EPSPs as a function of stimulus voltage. Open circles are EPSP amplitudes (r= 0.97; n = 30). Blue circles are EPSP slope measurements that were scaled to match the amplitude data (r= 0.83; n = 30). Solid lines represent fits by linear regression. , () an experiment showing changes in FV amplitudes (gray circles) and scaled slopes (green triangles) as stimulus voltage was increased and decreased. EPSP amplitudes (open circles) are plotted together with scaled EPSP slopes (blue triangles). Although the stimulus voltage was changed over a 3–6 V range there was no change in facilitation (solid black line). , Isoflurane depressed EPSPs (white and gray circles) and increased facilitation (black diamonds). , Low external Ca(0.8 mM) depressed EPSPs and increased facilitation. , 60 nM TTX depressed EPSPs while facilitation remained unchanged. Note that changes in the stimulus voltage in all three experiments (appearing as ramps in EPSP amplitudes) did not affect facilitation

Isoflurane depresses hippocampal CA1 glutamate nerve terminals without inhibiting fiber volleys-1

<p><b>Copyright information:</b></p><p>Taken from "Isoflurane depresses hippocampal CA1 glutamate nerve terminals without inhibiting fiber volleys"</p><p>BMC Neuroscience 2006;7():5-5.</p><p>Published online 12 Jan 2006</p><p>PMCID:PMC1369004.</p><p>Copyright © 2006 Winegar and MacIver; licensee BioMed Central Ltd.</p>ntrol responses are shown in black and isoflurane-depressed EPSPs are in blue. () Isoflurane reduced the slope of the FV-EPSP relation (blue circles). , () EPSP amplitudes were strongly decreased when external Cawas reduced from 2 mM to 0.8 mM. () slope of the FV-EPSP relation was reduced by 0.8 mM Ca(blue circles). , () reduction of EPSP and FV amplitudes by tetrodotoxin (TTX; 60 nM). () no change in the FV-EPSP relation in the presence of TTX. All FV-EPSP relations were well fit by single exponential functions

Isoflurane depresses hippocampal CA1 glutamate nerve terminals without inhibiting fiber volleys-4

<p><b>Copyright information:</b></p><p>Taken from "Isoflurane depresses hippocampal CA1 glutamate nerve terminals without inhibiting fiber volleys"</p><p>BMC Neuroscience 2006;7():5-5.</p><p>Published online 12 Jan 2006</p><p>PMCID:PMC1369004.</p><p>Copyright © 2006 Winegar and MacIver; licensee BioMed Central Ltd.</p>epresentative whole-cell perforated patch in the pyramidal cell body layer of the hippocampal CA1 region. 100 ms voltage pulses to -30 mV were applied at 10 s intervals to elicit spikes (V= -70 mV). Currents in green show four spikes recorded after a 15 min exposure to 60 nM TTX. At right are overlays of spike currents recorded before and after a 10 min exposure to 350 μM isoflurane (1 MAC). The blue traces were recorded after exposure to isoflurane

Subconductance block of single mechanosensitive ion channels in skeletal muscle fibers by aminoglycoside antibiotics

ABSTRACT The activity of single mechanosensitive channels was recorded from cellattached patches on acutely isolated skeletal muscle fibers from the mouse. The experiments were designed to investigate the mechanism of channel block produced by externally applied aminoglycoside antibiotics. Neomycin and other aminoglycosides reduced the amplitude of the single-channel current at negative membrane potentials. The block was concentrationdependent, with a half-maximal concentration of ~200 tzM. At high drug concentrations, however, block was incomplete with roughly one third of the current remaining unblocked. Neomycin also caused the channel to fluctuate between the open state and a suhconductance level that was also roughly one third the amplitude of the fully open level. An analysis of the kinetics of the subconductance fluctuations was consistent with a bimolecular reaction between an aminoglycoside molecule and the open channel (kon =,--d • 106 M-is-1 and koff = ~400 s-1 at-60 mV). Increasing the external pH reduced both the rapid block of the open channel and the frequency of the subconductance fluctuations, as if both blocking actions were produced by a single active drug species with a pK ~ = ~7.5. The results are interpreted in terms of a mechanism in which an aminoglycoside molecule partially occludes ion flow through the channel pore