Force and membrane potential in acetylcholine and potassium contractures of denervated mouse muscles

Stable Gastric Pentadecapeptide BPC 157 and Striated, Smooth, and Heart Muscle

First, we review the definitively severed myotendinous junction and recovery by the cytoprotective stable gastric pentadecapeptide BPC 157 therapy, its healing that might combine both transected and detached tendon and transected muscle, ligament and bone injuries, applied alone, as native peptide therapy, effective in rat injury, given intraperitoneally or in drinking water or topically, at the site of injury. As a follow up, we reviewed that with the BPC 157 therapy, its cytoprotective ability to organize simultaneous healing of different tissues of and full recovery of the myotendinous junction might represent the particular muscle therapy against distinctive etiopathology muscle disabilities and weakness. In this, BPC 157 therapy might recover many of muscle disabilities (i.e., succinylcholine, vascular occlusion, spinal cord compression, stroke, traumatic brain injury, severe electrolyte disturbances, neurotoxins, neuroleptics, alcohol, serotonin syndrome and NO-system blockade and tumor-cachexia). These might provide practical realization of the multimodal muscle-axis impact able to react depending on the condition and the given agent(s) and the symptoms distinctively related to the prime injurious cause symptoms in the wide healing concept, the concept of cytoprotection, in particular. Further, the BPC 157 therapy might be the recovery for the disabled heart functioning, and disabled smooth muscle functioning (various sphincters function recovery). Finally, BPC 157, native and stable in human gastric juice, might be a prototype of anti-ulcer cytoprotective peptide for the muscle therapy with high curing potential (very safe profile (lethal dose not achieved), with suited wide effective range (µg-ng regimens) and ways of application).

Effects of denervation on Ca2+ channels in slow skeletal muscle fibers of the frog

Effects of denervation on calcium channels in slow skeletal muscle fibers in the frog (Rana pipiens) were studied using the three-microelectrode voltage-clamp technique in intact fibers. Ca2+, Ba2+, and Sr2+ currents were all significantly reduced in amplitude during the first 2 weeks after denervation. After nerve section the selectivity sequence Ba congruent with Ca > Sr was changed to Ba > Sr > Ca and the values for relative ratio increased from 1.04 to 2.65 for Ba2+ and from 0.58 to 1.20 for Sr2+ (with respect to Ca2+). Barium current saturation was more obvious in denervated fibers than in non-denervated fibers. The values obtained with the Michaelis-Menten type expression, I = Imax/(1+Kd/[Ba]e) were Kd = 2.7 mM and Imax = 20 microA/cm2 in fibers 2 weeks after nerve section compared with the values Kd = 4.4 mM and Imax = 60 microA/cm2 obtained in non-denervated fibers. Additionally, the effects of two calcium channel blockers (cobalt and nifedipine) were greater by a factor of two in denervated fibers than in non-denervated fibers. Three weeks or so after nerve section, all the biophysical properties studied began to show a tendency to recover toward the values obtained in non-denervated muscles (controls). These results suggest that calcium channels are modified or that there is a change in the types of calcium channels present in frog slow skeletal muscle fibers after denervation.

Acetylcholine contractures of skeletal muscles: inhibition by chlorpromazine and diltiazem

The maximum contractures evoked by 100 microM ACh of mouse soleus muscles denervated for 3-7 days are completely inhibited by a 10 min exposure to 100 microM chlorpromazine (CP). Recovery on washout of CP takes more than 1 hr to complete. ACh evoked contractures are also inhibited by diltiazem (D); washout of D is immediately followed by recovery. Electrically evoked twitches and K evoked contractures are largely unaffected by CP, caffeine evoked contractures are decreased but not abolished. Fast mouse and (non-denervated) frog tonic muscles behave similarly. Depolarization by ACh and ACh-evoked whole cell currents show enhanced desensitization at low, and block at high [CP] and [D]; more than 50% recovery is achieved by less than 1 min washout of CP and D. Currents carried by Na+ and Mg2+ ions behave similarly. It is concluded that activation of ACh evoked contractures may be blocked by CP independent of ionic currents through nicotinic ACh receptors and that it depends on intracellular processes linked to these receptors.

Calcium current activation and charge movement in denervated mammalian skeletal muscle fibres

1. Calcium current (ICa) activation was studied in denervated extensor digitorum longus muscle fibres of the rat. Denervation was performed by surgically removing 6-8 mm of the sciatic nerve at the sciatic notch. Controls were normal fibres from non-operated rats. Electrical recordings were carried out using the double Vaseline-gap technique. 2. Current-voltage (I-V) curves showed that the ICa amplitude increased during the first 4-6 days after denervation and subsequently decreased during the second week. Between days 4 and 6 after denervation, the peak ICa amplitude (at 0 mV) was -5.9 +/- 0.5 microA/microF (mean +/- S.E.M.) as compared with -4.8 +/- 0.3 microA/microF in normal fibres. Between days 14 and 15 after denervation, the ICa amplitude was -2.9 +/- 0.4 microA/microF. 3. The time constant of ICa activation (tau a) was significantly increased by denervation. At 0 mV, tau a in normal fibres was 44.8 +/- 1.4 ms. Between 4 and 6 days after denervation tau a was 58.1 +/- 4.8 ms, and between 14 and 15 days after denervation, 55.8 +/- 3.8 ms. 4. The time constant of deactivation (tau d) decreased after denervation. At -10 mV, the tau d in normal fibres was 103.4 +/- 14 ms. The value decreased to 74.5 +/- 8.6 and 74.0 +/- 17 ms between days 4 and 6 and days 14 and 15 of denervation respectively. 5. Charge movement (Qon) was reduced progressively without major changes in the steepness (k) and position on the voltage axis of the Qon-Vm relationship. The fitted parameters under control were Qmax = 15.4 nC/microF, mid-point potential Vq1/2 = -25.2 mV and k = 11.9 mV. Between days 14 and 15 of denervation, the values for Qmax, Vq1/2 and k were 6.7 nC/microF, -36.8 mV and 11.3 mV respectively. 6. Calcium permeability (PCa) in normal and denervated fibres at stages during denervation was calculated according to the Hodgkin-Huxley model. At 0 mV PCa was 1.24 x 10(-5) cm/s in normal fibres, and 7.43 x 10(-6) cm/s after 2 weeks of denervation. 7. The m infinity-Vm relationship was shifted to more positive potentials after denervation without significant changes in the steepness factor k. The V1/2 value in normal fibres was -4.4 mV, and 5.8 mV after two weeks of denervation. 8. The ICa sensitivity to nifedipine was not modified in the different groups of denervated fibres studied. With 10 microM-nifedipine, the 1-(ICa in nifedipine/ICa control) relationships were 0.74 +/- 0.03 in normal fibres and 0.76 +/- 0.12, 14 days after denervation.

Mechanical and electrical properties of denervated rat skeletal muscles

Mechanical activity (twitch and tetanus) and electrical activity (single and repetitive action potentials) were recorded in vitro (34 degrees C) in control and denervated (3 to 14 days) soleus and extensor digitorum longus muscles of the rat. After denervation tetanic tension (100 to 200 Hz, 500 ms duration) was decreased in both types of muscles. Denervation reduced significantly the rates of rise and fall and the amplitude of the action potential in both types of muscle fibers. In denervated fibers with very low resting membrane potential no action potentials could be recorded: in these fibers only a slow response without overshoot was detected. Hyperpolarization of denervated fibers to -90 mV prior to application of the depolarizing pulse increased their excitability. Action potential amplitudes were well maintained during tetanic stimulation (200 Hz, 40 to 90 ms) in innervated fibers. Depolarization of the innervated fibers with cathodic current before the tetanic pulse hindered the generation of repetitive action potentials at 200 Hz. A proportion of denervated fibers stimulated at 100 to 200 Hz generated only one action potential or gave rise to an incomplete train. Hyperpolarization of the denervated fibers resulted in an improvement in the ability to generate a train of action potentials at 100 to 200 Hz. A group of denervated fibers exhibited well maintained action potentials during tetanus. We suggest that failure in the repetitive electrical activity of denervated fibers could be the reason for the reduced tension of tetanus. Depolarization of the fibers and/or the increment in the electrical time constant of the sarcolemma are suggested for the decrease in the electrical excitability of denervated fibers.