Rapid stimulatory effects of testosterone upon myotubule metabolism and sugar transport, as assessed by silicon microphysiometry

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A considerable number of studies bave revealed bebavioral circumstances tbat give rise to small or transient differences in circulating testosterone concentrations; however, carefut consideration of androgen physiology leads to tbe disquieting conclusion that these differences are often untikely to have much physiotogic or behavioral significance. In the present report, we observe that small transients of testosterone secretion could have very rapid anabolic effects on a cultured muscle-derived cell line. Specifically, we have examined the effects of testosterone on metabolism in cultured C2CI2 myotubules, using a silicon microphysiometer. The instrument monitors cellular extrusion of protons and acidic metabolites, and such extrusion is directly linked to ATP hydrolysis, thus providing a real-time measure of cellular metabolism. Te.stosterone caused a small but significant increase in metabolism. Tbe most striking feature of this effect wa.s its rapidity, in that it occurred within 3 br. This rapid enhancement of metabolism suggested that testosterone might be enhancing substrate uptake even more rapidly. Indeed., we found that testosterone increased 2-deoxyglucose uptake within I min. The rapidity of this effect seemed to preclude mediation by classical Intracellular steroid receptors. In support of this, we were unahle to detect specific intracellular binding of testosterone. These findings sbow that testosterone can exert rapid anabolic effects on substrate transport and metabolism in myotuhules. Should this finding general to muscle in vivo, it suggests that relatively small individual differences in testosterone profiles, in response to various social interactions, may have very real consequence for subsequent muscle physiology. © 19% Wilej-Liss, Inc.