P-type channels, a recently described form of voltage-gated calcium channels, are found in many central and peripheral neurons. In the present study, a partial cDNA clone sharing extensive nucleotide identity with a putative P-type voltage-gated calcium channel alpha 1 subunit was isolated from a small-cell lung carcinoma (SCLC) cell line. Anti-peptide antibodies generated to a unique acidic stretch in the IVS5-S6 linker region of the putative SCLC P-type channel reacted specifically with a SCLC fusion protein produced in bacteria and with a cell surface molecule in SCLC cells. Calcium currents in SCLC cells, measured by whole-cell patch clamp, were inhibited by these antibodies and by the P-type channel-specific toxin omega-agatoxin IVA. The inhibitory effects of the antibody and the toxin were not additive, consistent with their proposed action on the same type of channel. These results provide evidence for the expression of P-type calcium channels by SCLC cells. The expression of neuron-related molecules by these cells is of particular interest because small-cell lung carcinoma is frequently associated with paraneoplastic disorders affecting the nervous system.