Reassessment of the electrophysiological effects of the antiarrhythmic agent quinidine in canine Purkinje fibers

Microelectrode techniques were used to re-examine the direct effects of quinidine on isolated canine Purkinje fibers. Our results confirmed the previous findings that quinidine in a dose-related manner suppressed spontaneous activity, prolonged effective refractory period and depressed the maximal rate of upstroke (dv/dt). Quinidine shifted the membrane response curves to the right of the voltage axis regardless of external K⁺ concentrations. The drug diminished the phase 2 plateau of the action potential indicating a possible inhibitory effect on calcium influx. Quinidine generally lengthened the action potential duration (ADP) but the extent of the increase varied with the site of recording along the Purkinje conduction system. The shorter APDs were lengthened far more than the longer APDs, thus dissimilar APDs became more uniform. Following the alteration of external K⁺ between 2 mM and 6 mM, the effects of quinidine on transmembrane characteristics, including the depression of dv/dt, remain constant with the exception of APD.     

The effect of n-alkanols on the stationary current voltage behavior and action potential of myelinated nerve

Stationary current voltage characteristics and the action potential of single myelinated nerve fibres were measured to examine the effect of $\text{n-}\text{alkanols}$ (methanol to octanol) on the electrophysiological function of the axon membrane. K⁺-depolarized membranes show alkanol-dependent shifts of $\text{V}{}_{\mathrm{<mtext>Tr</mtext>}}$, the membrane transition voltage, whereas in veratridine-depolarized membranes such $\text{V}{}_{\mathrm{<mtext>Tr</mtext>}}\text{-}\text{shifts}$ are not observed. In the latter case, $\text{n-}\text{alkanols}$ reduce both the stationary Na⁺ current and the conductivity step between the high- and low-ohmic conductivity state of the membrane. Action potential amplitude, however, is less affected by the alkanols as is the stationary Na⁺ current. The results are compared with the alkanol-dependent changes of the thermotropic phase transition in phospholipid bilayers.     

Electrophoretic measurements about the relation between transition voltage and ζ-potential of biological membranes

The effects of inorganic cations, $\text{n-}\text{hexanol}$, saccharose and ²H₂O on the electrophoretic mobility and ζ-potential of membrane vesicles from nerve myelin were measured and the results compared with the corresponding effects of the same reagents on the transition voltage, $\text{V}{}_{\mathrm{<mtext>Tr</mtext>}}$, of the nerve axon membrane. Different cation concentrations and ²H₂O affect both potentials, the ζ-potential and $\text{V}{}_{\mathrm{<mtext>Tr</mtext>}}$, in a parallel way. Saccharose and $\text{n-}\text{hexanol}$, however, shift $\text{V}{}_{\mathrm{<mtext>Tr</mtext>}}$ but leave the electrophoretic mobility of the myelin vesicles unchanged. These results suggest that $\text{V}{}_{\mathrm{<mtext>Tr</mtext>}}$ shifts are not necessarily linked to changes in the membrane surface charge density but may also be caused by an interaction between the reagent and non-polar groups of the membrane interior.     

Utilization of C20-polyunsaturated fatty acids by a yeast fatty acid desaturase mutant

A study was made of the utilization of C₂₀-polyunsaturated fatty acids by the $\text{S. cerevisiae}$ fatty acid desaturase mutant $\text{olel-1}$, Arachidonic acid, 8,11,14-eicosatrienoic acid, and 5,8,11,14,17-eicosapentaenoic acid were about equally effective in supporting growth with lactate as the carbon source. The relative proportion of these fatty acids in total cell fatty acids was $\text{ca}$. 50%. 5,8,11-eicosatrienoic acid synthesized from oleate was less effective. Very little growth occurred with 11,14,17-eicosatrienoic acid or with 11,14-eicosadienoic acid. These results indicate the usefulness of the yeast mutant as a eucaryotic model for study of membrane systems enriched in specific C₂₀-polyunsaturated fatty acids.     

PGH2, TxA2 and PGI2 have potent and differentiated actions on human uterine contractility

The contractile response to three different prostanoids of the isolated human myometrium and the different layers of the utero-tubal junction (UTJ) was studied $\text{in vitro}$. The prostaglandin endoperoxide, PGH₂, stimulated contractility of both the myometrium and the outer and inner muscle layers of the UTJ, whereas the intermediate layer of the UTJ was inhibited. Thromboxane A₂ generated from PGH₂ and a thromboxane synthase preparation caused a stimulation of both the myometrium and all three layers of the UTJ. The stimulatory response to TxA₂ occurred at concentrations as low as 50–70 pg/ml. The sodium salt of PGI₂ was found to relax both the myometrium and all the layers of the UTJ. Intravenous administration of PGI₂ in repeated doses between 2–8 μg induced facial flushing and headache but had little if any effect on $\text{in vivo}$ uterine contractility. At least under $\text{in vitro}$ conditions, these short-lived prostanoids and/or their metabolites apparently have a specific action on uterine contractility, an action which is manifested at comparatively low concentrations.