Section of Pharmacology, Dept. of Pharmacobiology, University of Bari “Aldo Moro” Via Orabona, 4, 70125 Bari, conte@farmbiol.uniba.it

The aging process leads to profound impairment of skeletal muscle performance. We previously observed that skeletal muscle decline is associated with a modification of chloride and potassium channel activity important to sustain excitability and to prevent fiber dysfunction due to metabolic alteration. Indeed, during aging we previously found a significant reduction of resting chloride conductance (gCl) in parallel with a reduction of ClC-1 expression (Pierno et al., 1999). Reduced activity of the ATP-dependent potassium (KATP) channels was also found in the aged rats with respect to the adults (Tricarico and Conte Camerino, 1994). Calcium homeostasis and contractile properties were modified in terms of cytosolic calcium increase and modification of the mechanical threshold (MT) for contraction, an index of excitation-contraction coupling. At the aim to understand if these modifications can be associated with a oxidative damage, proposed to be one of the cause of senescence, we tested the effects of a phenolic antioxidant MIX derived from olive oil production process containing hydroxytirosol, homovanillic acid and gallic acid on skeletal muscles of 27-months-old rats. At the end of 8-weeks treatment we analyzed the resting gCl and the mechanical threshold for contraction by current clamp and point voltage clamp electrophysiological techniques. KATP channel activity was determined by patch clamp and calcium homeostasis by using FURA-2 cytofluorimetric technique. As expected, gCl was lower in aged animals with respect to the adults, being 1787±59 mS/cm2 (5 rats/37 fibers) and 2800±89 mS/cm2 (4 rats/30 fibers), respectively, and was partially restored in treated animals (2094±43 mS/cm2, 5 rats/41 fibers, P<0.001). Also the potassium conductance (gK), increased during aging, was restored toward the adult value. When applied in vitro, 100-500 microM of MIX induce a reduction of gCl at the higher concentration and an increase of gK, likely by a direct effect. The KATP channel activity was found to be significantly increased in treated animals toward the adult value. Also the resting intracellular calcium and MT were restored by the antioxidant treatment, although sarcolemma permeability was not modified. Since we previously found a modification of RyR activity during aging (Fraysse et al., 2006), we evaluated here the effects of caffeine application in skeletal muscle of these animals. Surprisingly, the response to caffeine in aged animals treated with MIX was similar to that found in the adult. Additional red-ox studies showed that the increase of malonil dialdehyde (MDA) level, as oxidative stress index, was slightly counteracted in the brain of treated rats. These findings suggest the beneficial effect of this compound to ameliorate skeletal muscle functional decline due to aging. (Supported by Regione Puglia PE-004)

Pierno et al. (1999). Eur J Pharmacol. 364, 43-8.
Tricarico and Conte Camerino (1994). Mol Pharmacol. 46, 754-61.
Fraysse et al. (2006). Neurobiol Dis. 21, 372-80.