Chloride channel regulation in the skeletal muscle of normal and myotonic goats

Abstract

External intercostal muscle biopsies from normal and congenitally myotonic goats were studied in vitro at 30 degrees C using a two-microelectrode square-pulse cable analysis assisted by computer. The resting chloride conductance (Gcl) was estimated from the difference between the mean membrane conductance in chloride-containing and chloride-free bathing media. The protein kinase C (PKC) activator, 4-beta-phorbol-12,13-dibutyrate. (0.1-2.0 microM) blocks a maximum of 76% of Gcl in normal goat fibers and induces myotonic hyperexcitability similar to that of congenitally myotonic goat fibers. The Gcl block was partially antagonized by pretreatment with the PKC inhibitor, staurosporine (10 microM). The "inactive" 4-alpha-phorbol-12,13-didecanoate had no effect at 50 microM, whereas the "active" 4-beta isomer blocked 41% Gcl at 1 microM. The nearly absent Gcl of congenitally myotonic goat fibers was not restored by treatment with high concentrations of the PKC inhibitors staurosporine, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7), or tetrahydropapaveralone (THP). Also, forskolin and cholera toxin, which may increase cyclic adenosine monophosphate (cAMP) levels, or the R(+) clofibric acid enantiomers and taurine, which increase Gcl in normal fibers, were also unable to restore Gcl in myotonic goat fibers. The data suggest that PKC may be a chloride channel regulator in normal goat skeletal muscle fibers, however the molecular defect of congenitally myotonic fiber does not appear to be due to excessive activity of PKC.

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

“…The muscles were perfused with normal or chloride-free physiological solutions (gassed with 95 % O 2 and 5 % CO 2 , pH 7.2-7.3). As previously detailed (Bryant and Conte Camerino 1991), the membrane electrical properties and the component conductances of the sarcolemma were determined in a current-clamp mode by means of the standard two-intracellular-microelectrode technique under computer control. A hyperpolarizing square current pulse (100-ms duration) was passed through one electrode and the membrane voltage response was monitored at two distances from the current electrode ).…”

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].…”

A Multidisciplinary Evaluation of the Effectiveness of Cyclosporine A in Dystrophic Mdx Mice

“…31 The two intracellular microelectrode current clamp method was used to measure the membrane electrical properties of muscle fibers by evaluating the attenuation of the electrotonic potential in response to standard hyperpolarizing current pulse at two distances between the recording and the current-injecting electrode, according to the cable equation. 32 Assuming constant value of fiber input resistance (Rin) of 140 and 200 ⍀ * cm for EDL and DIA muscle fibers, 31 respectively, it was possible to calculate membrane cable parameters, among which was membrane resistance (Rm). The total membrane conductance (gm) was calculated as 1/Rm in normal physiological solution, whereas 1/Rm calculated in a chloride-free solution was the potassium conductance gK.…”

“…Chloride conductance (gCl) was calculated as the mean gm minus the mean gK. 31,32 The mechanical threshold (MT) of the fibers was determined in EDL muscle fibers in normal physiological solution using a two microelectrode point voltage clamp method as previously described. 9,33 In brief, the two microelectrodes were inserted within 5 m of each other into the central region of a randomly selected superficial fiber that was continuously viewed using a stereomicroscope (ϫ100 magnification).…”