Calcium Channel Antibody, P/Q-Type Unit Converter

P/Q-type calcium channel antibody is an autoantibody that targets P/Q-type voltage-gated calcium channels (VGCCs), which are proteins located at the presynaptic nerve terminals throughout the nervous system. These channels control the flow of calcium into nerve endings, which is essential for releasing acetylcholine and other neurotransmitters that signal muscles and other cells.

When the immune system mistakenly produces antibodies against these channels, the antibodies bind to and remove the channels from the nerve terminal surface. This reduces calcium entry and impairs neurotransmitter release, leading to muscle weakness and autonomic dysfunction.

P/Q-type VGCC antibodies are detected in approximately 85-95% of patients with Lambert-Eaton myasthenic syndrome (LEMS) and are considered nearly 100% specific for LEMS in patients presenting with muscle weakness. They are also found in about 40% of patients with paraneoplastic cerebellar degeneration associated with small cell lung cancer.

P/Q-type calcium channels are found at presynaptic nerve terminals throughout the nervous system, including the neuromuscular junction and cerebellar Purkinje cells. In paraneoplastic cases (50-60% of LEMS), antibody production is triggered by small cell lung cancer cells that express these calcium channels, causing the immune system to produce cross-reactive antibodies. In non-paraneoplastic cases, the antibodies arise from autoimmune dysregulation, often associated with the HLA-B8-DR3 genetic haplotype.