The effect of increasing extracellular calcium concentration on spontaneous transmitter release was studied at both soleus (slow) and fast extensor digitorum longus (EDL) nerve terminals of control and streptozotocin-induced diabetic (STZ-D) young C57 BL mice (7 months old) depolarized by high (20 mM) extracellular potassium [K]o. Diabetes was induced by i.p. injection with a single dose of streptozotocin (200 mg/kg) at the age 5 months and the electrophysiological studies were carried out after 8 more weeks. By using intracellular recording, miniature endplate potentials (MEPPs) were first recorded in a normal [K]o Krebs solution. Subsequently, MEPPs were recorded in high [K]o Krebs solution with 4 different Ca concentrations: Ca-free/ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetra acetic acid (EGTA), 0.5, 1.5 and 2 mM Ca. MEPP frequency was lower at STZ-D than control nerve terminals in EDL but not soleus. However, MEPP frequency was progressively higher at both EDL and soleus of STZ-D than control with increasing Ca concentration in Krebs that contained 20 mM [K]o. In STZ-D slow soleus muscle, depolarization produced 0.7, 4.3, 41.6 and 62.7 vs 1.4, 2.8, 20.7 and 31.6 Hz for control in the 4 different Ca concentrations. In STZ-D fast EDL muscle, depolarization produced 0.5, 4.9, 48.2 and 66.8 vs 1.2, 2.5, 27 and 35.4 Hz for control in the 4 different Ca concentrations. Bimodal and unimodal MEPP amplitude were present at both slow and fast nerve terminals. However, depolarization increased the percentage of bimodal MEPP amplitude in STZ-D compared to control (p<0.01) mice in EDL but not soleus. The results revealed that these changes in muscle firing pattern may provide a protective effect against diabetes-induced neuropathy at the neuromuscular junction.
|Number of pages||5|
|Journal||Cellular and molecular biology (Noisy-le-Grand, France)|
|Publication status||Published - Mar 1999|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology