SEASONAL-VARIATION IN THE PROPERTIES OF MUSCLE MITOCHONDRIA FROM THE TROPICAL SCALLOP EUVOLA (PECTEN) ZICZAC

In scallops, gametogenesis leads to considerable transfer of energetic reserves from the adductor muscle to the gonads. During an annual cyc le, the scallops are exposed to changes in temperature and food availa bility. As these changes may affect muscle metabolic capacities, we ex amined whether the properties of the mitochondria in the phasic adduct or muscle were modified during the annual cycle of the scallop Euvola (Pecten) ziczac (L. 1758). During our study, temperature and chlorophy ll a levels generally showed an inverse relationship: high temperature s and low chlorophyll a levels occurred from mid-April to early June. Lower temperatures and higher chlorophyll a levels were found from Jan uary to late March and from mid-June to mid-September. Throughout the annual cycle, the substrate preferences and the pH sensitivity of the isolated muscle mitochondria changed little, whereas the maximal oxida tive capacities and respiratory control ratios (RCR) varied considerab ly. Consistently, the maximal capacities for substrate oxidation were 30 to 80% lower in mitochondria isolated in May than at other times in the year. The RCR values of mitochondrial oxidation of glutamate, glu tamine and succinate varied throughout the year with lower values char acterizing the mitochondria from scallops harvested in May and in cert ain cases in August. In May, adductor muscles had lower protein levels than at other times. These data suggest that the requirements of game togenesis, coupled with the high temperatures and low food availabilit y occurring during April and May, led to a mobilization of muscle prot eins which concomitantly decreased the oxidative capacity of isolated mitochondria.