Redistribution of Cav2.1 channels and calcium ions in nerve terminals following end-to-side neurorrhaphy: ionic imaging analysis by TOF-SIMS.

The P/Q-type voltage-dependent calcium channel (Cav2.1) in the presynaptic membranes of motor nerve terminals plays an important role in regulating Ca transport, resulting in transmitter release within the nervous system. The recovery of Ca-dependent signal transduction on motor end plates (MEPs) and innervated muscle may directly reflect nerve regeneration following peripheral nerve injury. Although the functional significance of calcium channels and the levels of Ca signalling in nerve regeneration are well documented, little is known about calcium channel expression and its relation with the dynamic Ca ion distribution at regenerating MEPs. In the present study, end-to-side neurorrhaphy (ESN) was performed as an in vivo model of peripheral nerve injury. The distribution of Ca at regenerating MEPs following ESN was first detected by time-of-flight secondary ion mass spectrometry, and the specific localization and expression of Cav2.1 channels were examined by confocal microscopy and western blotting. Compared with other fundamental ions, such as Na and K, dramatic changes in the Ca distribution were detected along with the progression of MEP regeneration. The re-establishment of Ca distribution and intensity were correlated with the functional recovery of muscle in ESN rats. Furthermore, the re-clustering of Cav2.1 channels after ESN at the nerve terminals corresponded with changes in the Ca distribution. These results indicated that renewal of the Cav2.1 distribution within the presynaptic nerve terminals may be necessary for initiating a proper Ca influx and shortening the latency of muscle contraction during nerve regeneration.