Optical properties of molecular nanocrystals consisting of J-aggregates of anionic and cationic cyanine dyes.

We report results of experimental studies of the photoabsorption, photoluminescent and photoelectric properties of a new type of multilayer molecular nanocrystals, consisting of highly ordered J-aggregates of one anionic and two cationic J-aggregates of cyanine dyes. In contrast to conventional J-aggregated dyes the multichromic nanocrystals synthesized in this work, are capable of efficient light absorption in three excitonic bands of the visible and near-IR spectral ranges. The spectral peak positions in the absorption bands can be controlled by appropriately selecting a set of dyes a molecular crystal is made of. Our investigations of the photoelectric properties of multichromic crystals have shown that each of them can potentially be used as a photosensitive layer of a photocell with photoconductivity in three peaks of excitonic absorption. The synthesized nanocrystals are attractive for the creation of thin-film organic photodetectors with a large photosensitive area and varied photoabsorption spectra, excitonic waveguides and for some other applications in organic and hybrid photonics and optoelectronics.

Specificity effects of run versus cycle training on ventilatory threshold.

This study compared the effects of 9 weeks of run (RT) versus cycle (CT) training on ventilatory threshold (Thv) determined during treadmill (TM) and cycle ergometer (CE) graded exercise testing. Sixteen college age men were assigned to a RT or CT group and performed a TM and a CE test before and after training. Both training groups performed similar training protocols which initially consisted of continuous exercise 4 days.week-1 at 75-80% maximum heart rate (fc, max) for 45 min. Training intensity was later increased to 80-85% fc, max and interval training (90-95% fc, max) was incorporated 2 days.week-1 into the continuous training. Both groups showed significantly improved maximal oxygen consumption (VO2 max) on both TM and CE tests (P < 0.01) with no significant differences between the groups. Significant Thv increases (P < 0.05) were found on TM tests for RT (n = 8) and CT (n = 8) groups [mean (SD); 443 (438) and 373 (568) ml O2 x min-1, respectively] with no difference between the groups. Results from the CE tests revealed a significant Thv increase (P < 0.01) for the CT group [566 (663) ml O2 x min-1] with no change for the RT group. The Thv improvement noted for the RT group was significantly different (P < 0.05) comparing CE with TM tests but not for the CT group. The results indicate that CT and RT improvement in Thv for runners is dependent upon mode of training and testing, and there is an apparent dissociation of VO2 max and Thv specific to training.

Alterations in sodium channel gating produced by the venom of the marine mollusc Conus striatus.

The action of the venom from the marine mollusc Conus striatus was studied using the voltage-clamp technique on myelinated nerve. Conus venom applied to an isolated node of Ranvier at 1.1 micrograms protein/ml produced repetitive firing of action potentials when the node was depolarized under current-clamp conditions. Venom application produced a leftword (depolarizing) shift in both the peak sodium current-voltage and the permeability-voltage relationships. A concomitant decrease in maximum peak current and permeability also occurred. The time course of sodium current decline (inactivation) was slowed at all voltages by the presence of venom. Venom treatment caused only a slight depolarizing shift (5 mV) in the voltage-dependence of steady-state Na inactivation. The closing to the resting state of previously activated Na channels, "deactivation", was judged from Na "tail" currents following membrane repolarization, and was slowed more than four-fold by venom treatment. The changes in Na channel gating produced by Conus striatus venom can best be described as a stabilization of the open state of the Na channel and a shift in the voltage dependence of the opening of Na channels. The slowing of both inactivation and deactivation of Na channels can be simulated by alterations in the rate constants of a five state Markov model.

Effects of strychnine on the potassium conductance of the frog node of Ranvier.

The nature of the block of potassium conductance by strychnine in frog node of Ranvier was investigated. The block is voltage-dependent and reaches a steady level with a relaxation time of 1 to several ms. Block is increased by depolarization or a reduction in [K+]O as well as by increasing strychnine concentration. A quaternary derivative of strychnine produces a similar block only when applied intracellularly. In general and in detail, strychnine block resembles that produced by intracellular application of the substituted tetraethylammonium compounds extensively studied by C.M. Armstrong (1969. J. Gen Physiol. 54:553-575. 1971. J. Gen. Physiol. 58:413-437). The kinetics, voltage dependence, and dependence on [K+]O of strychnine block are of the same form. It is concluded that tertiary strychnine must cross the axon membrane and block from the axoplasmic side in the same fashion as these quaternary amines.

Effects of strychnine on the sodium conductance of the frog node of Ranvier.

Strychnine blocks sodium conductance in the frog node of Ranvier. This block was studied by reducing and slowing sodium inactivation with scorpion venom. The block is voltage and time dependent. The more positive the axoplasm the greater the block and the faster the approach to equilibrium. Some evidence is presented suggesting that only open channels can be blocked. The block is reduced by raising external sodium or lithium but not impermeant cations. A quaternary derivative of strychnine was synthesized and found to have the same action only when applied intracellularly. We conclude that strychnine blocks sodium channels by a mechanism analogous to that by which it blocks potassium channels. The potassium channel block had previously been found to be identical to that by tetraethylammonium ion derivatives. In addition, strychnine resembles procaine and its derivatives in both its structure and the mechanism of sodium channel block.

Negative surface charge near sodium channels of nerve: divalent ions, monovalent ions, and pH.

Evidence is given for a high density of negative surface charge near the sodium channel of myelinated nerve fibres. The voltage dependence of peak sodium permeability is measured in a voltage clamp. The object is to measure voltage shifts in sodium activation as the following external variables are varied: divalent cation concentration and type, monovalent concentration, and pH. With equimolar substitution of divalent ions the order of effectiveness for giving a positive shift is: Ba equals Sr less than Mg less than Ca less than Co approximately equal to Mn less than Ni less than Zn. A tenfold increase of concentration of any of these ions gives a shift of +20 to +25 mV. At low pH, the shift with a tenfold increase in Ca-2+ is much less than at normal pH, and conversely for high pH. Soulutions with no added divalent ions give a shift of minus 18 mV relative to 2 mM Ca-2+. Removal of 7/8 of the cations from the calcium-free solution gives a further shift of minue 35 mV. All shifts are explained quantitatively by assuming that changes in an external surface potential set up by fixed charges near the sodium channel produce the shifts. The model involves a diffuse double layer of counterions at the nerve surface and some binding of H+ions and divalent ions to the fixed charges. Three types of surface groups are postulated: (1) an acid pKa equals 2.88 charge density minus 0.9 nm- minus 2; (i) an acid pKa equals 4.58, charge density minus 0.58 nm- minus 2; (3) a base pKa equals 6.28, charge density +0.33 nm- minus 2. The two acid groups also bind Ca-2+ ions with a dissociation constant K equals 28 M. Reasonable agreement can also be obtained with a lower net surface charge density and stronger binding of divalent ions and H+ ions.

Hodgkin-Huxley axon. Increased modulation and linearity of response to constant current stimulus.

Repetitive response patterns resembling those of tonic receptors were obtained by increasing the potassium system time constant in the Hodgkin-Huxley (H-H) equations. The increase in time constant varied with membrane potential. Calculated spike frequencies varied linearly with the magnitude of the constant current stimulus; in addition, minimum frequencies were greatly reduced, and the frequency range increased. Modification of the maximum ionic conductances, membrane capacitance, and rate constant voltage dependence was found to vary the minimum frequency, current at that frequency, slope, and over-all modulation of the modified responses.

Condylactis toxin: interaction with nerve membrane ionic conductances.

A toxin from the Bermuda anemone Condylactis gigantea causes the early transient conductance change of crayfish giant axon membranes to persist without affecting the shape of its turning-on. The increase in late steadystate conductance is either not affected or slightly suppressed. The effect on the conductance components can adequately account for the prolonged action potential observed in the treated axon.