Stable cell lines are potentially excellent tools for large-scale screening of new compounds. Two carboxyterminal-deleted constructs of the two splice variants a and b of the calcium channel class C alpha 1 subunit were expressed stably in HEK 293 cells. Each cell line produced regular L-type calcium currents. The opening and closing of the calcium channel elicited by potassium depolarization was followed by Fura-2 transients. These transients were blocked by the calcium channel blocker mibefradil with a concentration for 50% inhibition of 1.7 microM. The cell lines expressing the truncated cardiac alpha 1C-a or smooth muscle alpha 1C-b calcium channel were both blocked by nisoldipine under patch clamp conditions. Nisoldipine interacted with higher affinity with the alpha 1C-b channel than with the alpha 1C-a channel. These results indicate that the two cell lines retain the differential dihydropyridine sensitivity of smooth muscle and cardiac calcium channels and may be potential tools for the screening of L-type calcium channel blockers.