Resting and spike potentials of skeletal muscle fibres of salt-water elasmobranch and teleost fish

1. Membrane properties of the muscle fibre were studied in twitch motor system of sea-water elasmobranch (Taeniura lymma, Himantura uarnak and Pastinachus sephen) and teleost fish (Periophthalmodon barbarus, Tetradon immaculata, Hemiramphus welsby, Parexocoetus brachypterus and Conger labiatus).2. The resting potential of the elasmobranch fibre is mainly determined by the Cl(-) concentration difference between inside and outside the membrane whereas the K(+) conductance is the determining factor in teleost fibres.3. The resting membrane of the elasmobranch fibre is permeable not only to Cl(-) ions but also several other anions (Br(-), I(-), NO(3) (-), SCN(-), ClO(4) (-), ClO(3) (-)) of large limiting conductivities in the aqueous solution.4. The spike potential of the elasmobranch fibre always shows a significant overshoot in normal saline while no significant overshoot is generally found in teleost fibres.5. In both elasmobranchs and teleosts the spike is produced by the permeability increase of the membrane to Na(+) ions and is effectively suppressed by tetrodotoxin at a concentration of 0.5-1.0 x 10(-7) g/ml. of the external solution with one exception, i.e. the Na(+) spike of Tetradon fibre is not suppressed by the toxin even when the concentration is above 5 x 10(-4) g/ml.

Surface density of calcium ions and calcium spikes in the barnacle muscle fiber membrane

The effects of various divalent cations in the external solution upon the Ca spike of the barnacle muscle fiber membrane were studied using intracellular recording and polarizing techniques. Analysis of the maximum rate of rise of the spike potential indicates that different species of divalent cations bind the same membrane sites competitively with different dissociation constants. The overshoot of the spike potential is determined by the density of Ca (Sr) ions in the membrane sites while the threshold membrane potential for spike initiation depends on the total density of divalent cations. The order of binding among different divalent and trivalent cations is the following: La+++, UO2++ > Zn++, Co++, Fe++ > Mn++ > Ni++ > Ca++ > Mg++, Sr++.

Post-tetanic hyperpolarization and electrogenic Na pump in stretch receptor neurone of crayfish

1. Two types of after-potentials in the stretch receptor neurone of crayfish are described.2. A short-duration after-hyperpolarization associated with a single spike or a few spikes is diminished and reversed on applying hyperpolarizing currents. However, a much longer-lasting post-tetanic hyperpolarization (PTH) is enhanced by conditioning hyperpolarization; thus, no reversal potential can be obtained.3. No changes in membrane conductance occur during PTH.4. Reducing K concentration in the bathing fluid diminishes PTH, while it shifts the reversal potential of the short after-potential toward greater negativity.5. Replacement of Na with Li, or addition of 2,4-dinitrophenol in the bathing fluid suppresses PTH in a reversible manner.6. Electrophoretic injection of Na into the cell induces a long-lasting hyperpolarization.7. No change in K-equilibrium potential, as indicated by the reversal point of the short after-potential, is detected during PTH.8. It is concluded that the short after-potential is caused by a permeability increase for potassium ion, whereas PTH is produced by an electrogenic Na-pump.