Differential expression of a1and b subunits of voltage dependent ca2+ channel at the neuromuscular junction of normal and P/Q ca2+ channel knockout mouse

PAGANI R., SONG M., MCENERY M., QIN N., TSIEN R.W., TORO L., STEFANI E. & UCHITEL O.D.

NEUROSCIENCE

Año: 2004 vol. 123 p. 75 - 85

0306-4522

Voltage-dependent calcium channels (VDCC) have a key role in neuronal function transforming the voltage signals into intracellular calcium signals. They are composed of the pore-forming a1 and the regulatory a2d, g and b subunits. Molecular and functional studies have revealed which a1 subunit gene product is the molecular constituent of each class of native calcium channel (L, N, P/Q, R and T type). Electrophysiological and immunocytochemical studies have suggested that at adult mouse motor nerve terminal (MNT) only P/Q type channels, formed by a1A subunit, mediate evoked transmitter release. The generation of a1A-null mutant mice offers an opportunity to study the expression and localization of calcium channels at a synapse with complete loss of P/Q calcium channel. We have investigated the expression and localization of VDCCs a1 and b subunits at the wild type (WT) and knockout (KO) mouse neuromuscular junction (NMJ) using fluorescence immunocytochemistry. The a1A subunit was observed only at WT NMJ and was absent at denervated muscles and at KO NMJ. The subunits a1B, a1D and a1E were also present at WT NMJ and they were overexpressed at KO NMJ suggesting a compensatory expression due to the lack of the a1A. On the other hand, the b1b, b2a and b4 were present at the same levels in both genotypes. The presence of other types of VDCC at WT NMJ indicate that they may play other roles in the signaling process which have not been elucidated and also shows that other types of VDCC are able to substitute the a1A subunit, P/Q channel under certain pathological conditions. Key words: neuromuscular junction, synaptic transmission, denervation, immunostaining, ataxia.