EFFECT OF CHRONIC LITHIUM-CHLORIDE ON MEMBRANE ADENOSINE TRIPHOSPHATASES IN CERTAIN POSTURAL MUSCLES OF RATS

Lithium has been extensively used as an antidepressant in the treatmen t of manic depressive disorders requiring chronic administration. Here , we report a study of the effect of long-term lithium treatment on th e activities of membrane adenosine triphosphatases (ATPases) in certai n postural muscles of rat. Specifically, Ca2+-ATPase, Na+,K+-ATPase an d Mg2+-ATPase activities were measured in the soleus, extensor digitor um longus and plantaris muscles following 6 weeks of treatment with Li CI. Increases were observed in the Na+,K+-ATPase activity whereas the Mg2+-ATPase activity decreased with prolonged LiCI treatment. The most pronounced effect was a highly significant (P < 0.001) increase in th e mitochondrial Ca2+-ATPase and Na+,K+-ATPase activity to almost 50-10 0% above the control. The increases in the mitochondrial Ca2+-ATPase a ctivity of extensor digitorum longus and plantaris were 70% and 100%, respectively. The corresponding increases in the Na+,K+-ATPase activit y were 127%, 99% and 87% for soleus, extensor digitorum longus and pla ntaris, respectively. Irrespective of the differences in the fiber pat tern and physiological function, all three muscles responded in a simi lar way to Li+. The changes in the membrane ATPases reflect a deranged ATP turnover, thus affecting the overall energy state of the animal. Based on these results, we hypothesize that Li+ produces its effects b y interfering with cation transport processes. Since Li+ affects the n eural excitability of the cell it is suggested that the stimulation of the ATPases may be important in the psychotropic properties of the io n.