CHRONIC ADMINISTRATION OF TAURINE TO AGED RATS IMPROVES THE ELECTRICAL AND CONTRACTILE PROPERTIES OF SKELETAL-MUSCLE FIBERS

A reduction of resting chloride conductance (GCI) and a decrease of th e voltage threshold for contraction are observed during aging in rat s keletal muscle. The above alterations are also observed in muscle of a dult rat after taurine depletion. As lower levels of taurine were foun d by others in aged rats compared to young rats, we tested the hypothe sis that a depletion of taurine may contribute to the alteration of th e electrical and contractile properties we found in skeletal muscle du ring aging. This was accomplished by evaluating the potential benefit of a pharmacological treatment with the amino acid. To this aim 25-mo- old Wistar rats were chronically treated (2-3 mo) with taurine (1 g/kg p.o. daily) and the effects of such a treatment were evaluated in vit ro on the passive and active membrane electrical properties of extenso r digitorum longus muscle fibers by means of current-clamp intracellul ar microelectrode technique. Excitation-contraction coupling was also evaluated by measuring the voltage threshold for contraction with the intracellular microelectrode ''point'' voltage clamp method. In parall el muscle and blood taurine contents were determined by high-performan ce liquid chromatography. Taurine supplementation significantly raised taurine content in muscle toward that found in adult rats. Supplement ation also significantly increased GCI vs, the adult value, in paralle l the excitability characteristics (threshold current and latency) rel ated to this parameter were ameliorated. The increase of GCI induced b y taurine was accompanied by a restoration of the pharmacological sens itivity to the R(+) enantiomer of 2-(p-chlorophenoxy) propionic acid, a specific chloride channel ligand. in parallel also the protein kinas e C-mediated modulation of the channel was restored; in fact the poten cy of 4-beta-phorbol 12,13-dibutyrate in reducing GCI was lower in tau rine-treated muscles vs, untreated aged, being rather similar to that observed in adult. The treatment also improved the mechanical threshol d for contraction of striated fibers which in aged rats is shifted tow ard more negative potentials, moving it toward the adult values. Our r esults suggest that the reduction of taurine content could play a role in the alteration of electrical and contractile properties observed d uring aging. These findings may indicate a potential application of ta urine in ensuring normal muscle function in the elderly.