Disuse of rat muscle in vivo reduces protein kinase C activity controlling the sarcolemma chloride conductance

Abstract

Muscle disuse produced by hindlimb unloading (HU) induces severe atrophy and slow-to-fast fibre type transition of the slow-twitch soleus muscle (Sol). After 2 weeks HU, the resting ClC-1 chloride conductance (g Cl ) of sarcolemma, which controls muscle excitability, increases in Sol toward a value typical of the fast-twitch EDL muscle. After 3 days of HU, the g Cl increases as well before initiation of fibre type transition. Since ClC-1 channels are acutely silenced by PKC-dependent phosphorylation, we studied the modulation of g Cl by PKC and serine-threonine phosphatase in Sol during HU, using a number of pharmacological tools. We show that a fraction of ClC-1 channels of control Sol are maintained in an inactive state by PKC basal activity, which contributes to the lower g Cl in control Sol compared to EDL. After 14 days of HU, PKC/phosphatase manipulation produces effects on Sol g Cl that corroborate the partial slow-to-fast transition. After 3 days of HU, the early increase of g Cl in Sol is entirely attributable to a reduction of PKC activity and/or activation of phosphatase, maintaining ClC-1 channels in a fully active state. Accordingly, we found that HU reduces expression of PKCα, ε, and θ isoenzymes in Sol and EDL muscles and reduces total PKC activity. Moreover, we show that the rheobase current is increased in Sol muscle fibres as soon as after 3 days of HU, most probably in relation to the increased g Cl . In conclusion, Sol muscle disuse is characterized by a rapid reduction of PKC activity, which reduces muscle excitability and is likely to contribute to disuse-induced muscle impairment.

An olive oil-derived antioxidant mixture ameliorates the age-related decline of skeletal muscle function

“…The muscle g Cl is mainly due to the activity of ClC-1 chloride channels. We previously demonstrated that the reduction of g Cl in aged rat muscles is due to a reduction of ClC-1 expression levels and the increased activity of PKC able to close the channel (De Luca et al 1994;Pierno et al 1999Pierno et al , 2007. Interestingly, it has been described that mitochondrial dysfunction and the consequent increase of ROS during aging produce an intracellular accumulation of diacylglycerol and the activation of different PKC isoforms, which may contribute to aging-related insulin resistance (Kim et al 2008).…”

Fiber Types in Mammalian Skeletal Muscles

“…Studies carried out in rat and mouse muscles show that chloride conductance is higher in fast compared with slow muscle, and this is due to the higher level of expression of ClC1 in fast fibers, but also to the greater inactivation of ClC1 mediated by protein kinase C (PKC) phosphorylation in slow fibers (109,612). Several conditions that induce a fiber type transition are associated with the expected changes in ClC1 expression (611) and with changes in PKC-mediated inactivation (612). C) POTASSIUM CHANNELS.…”

Statin or fibrate chronic treatment modifies the proteomic profile of rat skeletal muscle

“…Indeed, lipophilic statin increased intracellular calcium via mitochondria and sarcoplasmic reticulum release [17], thereby affecting contractile function. In turn these drugs reduced resting gCl [18][19], a parameter sustained by the ClC-1 chloride channel and modulated by calcium-dependent PKC [20][21][22][23][24][25]. This parameter is normally high in fast-twitch muscles and is important to guarantee muscle membrane potential and excitability [20][21][22].…”