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New push–pull conjugated polymers based on furo[3,4-c]pyrrole-4,6-dione (FPD) and selenopheno[3,4-c]pyrrole-4,6-dione (SePD) have been synthesized and compared with their thieno[3,4-c]pyrrole-4,6-dione (TPD) analogues to investigate the effects of the heteroatom on the electrooptical properties. The copolymers were synthesized using either Stille cross-coupling or direct heteroarylation polymerization (DHAP), the latter method giving high molecular weights. Hypsochromic shifts of the band gaps were observed for FPD-based copolymers (sulfur substituted by oxygen) while small bathochromic shift was observed for SePD (sulfur substituted by selenium) when compared to its TPD analogue. These two new classes of conjugated polymers exhibit electrooptical properties that could lead to interesting bulk heterojunction plastic solar cells.

A reevaluation of the secondary structure of Na, Ca and K channel proteins led to the following results. Only three segments (S1, S5 and S6) of each repeat are sufficiently hydrophobic to be predicted as transmembrane helices, if a window of 19 amino acids is used. Some of the S2 and S3 segments show higher hydrophobic values when calculated with the window of 9 amino acids and can be predicted as short helices. S4 segments are strongly hydrophilic and cannot be predicted as transmembrane helices. Some of the S2, S3 and S4 segments have an amphipathic character; however, these helices do not span a membrane. A model is proposed where 12 hydrophobic transmembrane helices surround 12 shorter helices, forming a hydrophilic pore. In addition, a unique pattern for S4 segments of voltage-gated channel proteins is defined.

The polyamine, spermine, if ionophoretically injected into identified molluscan neurons, reduces the amplitude of action potentials and alters their wave form. Spermine cations block both, the calcium inward current and the delayed potassium outward current in a dose dependent manner. The block of the ionic currents by spermine cations can be described as a voltage dependent reaction.

1. (1) Changes of the holding potential applied to the membrane of myelinated nerve fibres induce slow variations of the peak sodium current, which are superimposed on the effect of sodium inactivation. 2. (2) These slow variations are transitions between various steady levels of available sodium conductance. Their time course can be described by the function erfc (√t/τ) where t is the time and erfc the error function complement. The characteristic time τ lies in the range 2–4 min and depends on the membrane potential. 3. (3) Changes of extracellular pH cause a rapid change of the peak sodium current followed by a slow variation as observed after changes of the holding potential. This slow variation can be prevented by applying simultaneously an appropriate change of the holding potential, e.g. the effect of changing pH from 7.3 to 5.3 is balanced by changing the potential from −70 to −55 mV. 4. (4) The results are interpreted by postulating charged components diffusing slowly within the nodal membrane. Their transverse distribution controls the number of sodium channels available at a given membrane potential. The equivalence between change of pH and voltage is explained by assuming negative fixed charges at the outer surface of the membrane, which are protonated at low pH and thus affect the intrinsic membrane potential. 5. (5) It is concluded that effects which are ascribed to the action of agents on individual sodium channels have to be corrected for variations in the number of available channels if these agents influence the intrinsic membrane potential, e.g. changes of extracellular pH.

The influence of monomeric methylmethacrylate (MMA) on resting and compound action potential of the isolated desheathed sciatic nerve of the frog (sucrose gap method) was determined. Above 10 mM there was a dose-dependent decrease of the compound action potential and a hyperpolarization of the membrane which was augmented with increasing MMA concentrations (4.1 mV +/- 0.2 S.E.M. after 50 mM MMA). The depolarization in low [Ca2+]0 solutions or with veratrine was reversed by MMA. The homologous ethyl, allyl and n-butyl esters were more effective than MMA, and the isobutyl ester less effective, whereas Na-methacrylate and methacrylamide showed no influence. Voltage clamp experiments on the node of Ranvier indicated that 50 mM MMA led to a decrease of the Na+ and K+ currents.

An equation for ionophoresis in large tip microelectrodes is derived from Nernst-Planck equations for the general case of a completely dissociated electrolyte. The relation between the release of ions and the applied electric current is mainly determined by two parameters: the transference number of the ions under consideration and the diffusional leak of the microelectrode. Also it is shown how the release of ions is affected by the concentration of the electrolyte within the electrode and that of the external solution. The equation describes the ionophoretic release of polyvalent spermine. In addition, new equations for tip potential and for tip resistance are derived.