Received August 28, 2007
Revised October 5, 2007
Accepted after revision October 25, 2007

¹ University of East Anglia

^* To whom correspondence should be addressed. E-mail: g.mutungi{at}uea.ac.uk.

	Abstract

Although numerous studies have recently implicated the calcineurin/nuclear factor of activated T cells (Cn/NFAT) signalling pathway in the regulation of activity dependent fibre type switching in adult mammalian skeletal muscles, little is known about the endogenous expression of NFAT proteins in the various fibre types present in these muscles. In this study, the immunolocalisation of NFATc1 (also known as NFATc; NFAT2) in the extensor digitorum longus (edl; a mainly fast-twitch muscle) and the selous (a predominantly slow-twitch muscle) muscles of adult (~90days) wistar rats was investigated. The results show that NFATc1 is expressed only in oxidative fibres (i.e. type 1 and type 2A fibres) that stain intensely for SDHase activity irrespective of whether they are from the fast- or slow-twitch muscle. Thus 99 ± 4% (n=7 rats) of the muscle fibres in the soleus and 42 ± 2 % (n=7 rats) of those in the edl expressed NFATc1. In the soleus muscle fibres, NFATc1 was localised mainly in the fibre nuclei; whereas in the edl fibres it was localised in both the cytoplasm and nuclei. However, no difference in its localisation was observed between type 1 and type 2A fibres in both muscles. Western blot experiments showed that the soleus expressed more NFATc1 proteins than the edl. From these results, we suggest that NFATc1 controls the number and distribution of both type 1 and type 2A fibres as well as the oxidative capacity of adult mammalian skeletal muscles.

Key Words: Cell signalling, Rat, Skeletal muscle