Biomedical subjects

W B Alshuaib

Publications and source records attributed to W B Alshuaib.

3 recordsLinked to original sources

PubMed1991

Depolarization reverses age-related decrease of spontaneous transmitter release.

The effect of increasing extracellular Ca concentration on spontaneous transmitter release was studied at soleus nerve terminals of young (10 mo) and old (24 mo) C57BL/6J mice depolarized by high extracellular K concentration ([K]o). By using intracellular recording, miniature end-plate potentials (MEPPs) were first recorded in a normal [K]o Krebs solution. Subsequently, MEPPs were recorded in high [K]o Krebs solutions with four different Ca concentrations: Ca-free/ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and 0.5, 1.5, and 2.5 mM Ca. In both the normal [K]o Krebs and the Ca-free-high [K]o Krebs solutions, MEPP frequency was lower at old than at young nerve terminals. In the three high [K]o Krebs solutions with Ca, MEPP frequency was progressively higher at old than at young nerve terminals with higher Ca concentrations. Periodic oscillations were observed in MEPP frequency of depolarized nerve terminals. The period of oscillation was inversely proportional to spontaneous transmitter release. These results demonstrate that when the nerve terminal is depolarized, permeability of the terminal membrane to Ca increases because of opening of voltage-dependent Ca channels. In the present study resting MEPP frequency was lower at old than at young terminals. On depolarization, MEPP frequency became higher at old than at young terminals. The study demonstrates that voltage-dependent Ca entry increases during aging at the soleus nerve terminal.

Aging↗

PubMed1990

Aging increases calcium influx at motor nerve terminal.

To determine whether increased transmitter release from soleus nerve terminals of old C57BL/6J mice is caused by an altered Ca2+ regulation, the time course of post-tetanic potentiation of miniature endplate potential (MEPP) frequency was used as an indicator of the kinetics of Ca2+ metabolism in young (10 months) and old (24 months) mice. Post-tetanic potentiation properties were studied in either (1) 0.2 mM Ca2+, 5.0 mM Mg2+ Krebs; or (2) Ca2(+)-free/EGTA Krebs to eliminate Ca2+ influx, and thereby isolated Ca2+ buffering. In the 0.2 mM Ca2+ Krebs, the time constants of decay of augmentation (TA) and potentiation (TP) were longer in old (TA = 10.3 +/- 1.0 sec, TP = 195.3 +/- 5.4 sec) than in young (TA = 7.0 +/- 0.7 sec, TP = 78.8 +/- 6.6 sec) nerve terminals. Evoked transmitter release was measured in 0.4 mM Ca2+, 2.75 mM Mg2+ Krebs. Quantal content of the endplate potential was positively correlated with TA (r = 0.95) and with TP (r = 0.98). In the Ca2(+)-free/EGTA Krebs, there was no difference in post-tetanic potentiation properties between young and old terminals. These results suggest that Ca2+ influx into the soleus nerve terminal increases with aging. This may explain, at least in part, the increased quantal content observed at old terminals.

Aging↗

PubMedDate not supplied

Effect of exercise on physiological age-related change at mouse neuromuscular junctions.

To determine the effect of endurance exercise on physiological age-related change at the mouse neuromuscular junction (NMJ), synaptic function was studied for extensor digitorum longus (EDL) and soleus muscles of three C57BL/6J mouse groups, 1) young adult control (YC: 10 months), 2) old control (OC: 20 months), and 3) old mice which exercised (OE: 20 months) since young-adulthood. Electrophysiological properties were studied with intracellular recording techniques. Safety margin was studied by measuring indirect isometric twitch tension in different calcium concentrations. With sedentary aging, EDL and soleus quantal contents increased. Following aging combined with 10 months of exercise, the EDL quantal contents in OE and YC animals were similar. In contrast, soleus quantal content was greater in OE than in YC animals. Determined safety margins were OC greater than YC = OE for EDL, and OC = YC = OE for soleus. This is the first study to indicate that physiological age-related changes at NMJs of EDL and soleus muscles are affected differently by endurance exercise. Exercise prevented all physiological age-related changes in EDL NMJs but not in soleus NMJs, this suggests that EDL changes are associated with inactivity during aging, while soleus changes are "fundamental" age changes.

Aging↗