Lactate efflux from fatigued fast-twitch muscle fibres of Xenopus laevis under various extracellular conditions.

1. Isolated, fast-twitch, low-oxidative muscle fibres from the iliofibularis muscle of Xenopus laevis were fatigued by intermittent tetanic stimulation at 20 degrees C in different Ringer solutions and the amount of lactate released was determined. 2.

ATP formation and ATP hydrolysis during fatiguing, intermittent stimulation of different types of single muscle fibres from Xenopus laevis.

This report describes changes of the rate of ATP hydrolysis in single, intact muscle fibres during the development of fatigue induced by intermittent tetanic stimulation. High (type 3) and low (type 1) oxidative muscle fibres dissected from the iliofibularis muscle of Xenopus laevis were studied at 20 degrees C. The rate of ATP hydrolysis was calculated during different time intervals from changes in the content of nucleotides, creatine compounds and lactate, as well as lactate efflux and oxygen uptake.

Metabolic changes with fatigue in different types of single muscle fibres of Xenopus laevis.

1. Peak isometric force of single fast (type 1) and slow (type 3) muscle fibres of Xenopus decreased when fibres were stimulated intermittently above their predicted sustainable duty cycle at 20 degrees C. Type 1 fibres could be fatigued to zero force.

The membrane stabilizing activity of beta-adrenoceptor ligands. Quantitative evaluation of the interaction of phenoxypropanolamines with the [3H]batrachotoxinin A 20-alpha-benzoate binding site on voltage-sensitive sodium channels in rat brain.

The interaction of 12 phenoxypropanolamines, all ligands with high affinity towards beta-adrenoceptors, with the [3H]batrachotoxinin A 20-alpha-benzoate ([3H]BTX-B) binding site on voltage-sensitive sodium channels in a rat brain synaptosomal preparation, was studied as a measure for local anaesthetic activity. All derivatives are capable of displacing [3H]BTX-B from its specific binding site, penbutolol displaying the highest affinity. Multiple regression analyses were performed, correlating biological activity (pKi values) with physicochemical parameters.