Changes in Fluorescence in a Frog Sartorius Muscle Following a Twitch

Abstract

IN a recent publication¹ it was proposed that the blue autofluorescence of living tissues may largely be due to the reduced pyridine nucleotide of the mitochondria. An opportunity to test this hypothesis is afforded by the specific response of the intramitochondrial pyridine nucleotide to an increase of concentration of adenosine diphosphate following a muscle twitch. This increase of concentration of adenosine diphosphate has been shown by spectro-photometric observations to cause an oxidation of reduced pyridine nucleotide of the mitochondria both in the isolated mitochondria² and intact muscles³. Thus muscle contraction elicits a specific response of intramitochondrial pyridine nucleotide. Such a specific test is required to distinguish between the fluorescence of cytoplasmic and mitochondrial pyridine nucleotides because both may be bound forms and therefore have indistinguishable maxima at 443 mµ⁴.