Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Smooth muscle exhibits mechanosensitivity independent of neural input, suggesting that mechanosensitive pathways reside within smooth muscle cells. The native L-type calcium current recorded from human intestinal smooth muscle is modulated by stretch. To define mechanosensitive mechanisms involved in the regulation of smooth muscle calcium entry, we cloned the alpha(1C) L-type calcium channel subunit (Ca(V)1.2) from human intestinal smooth muscle and expressed the channel in a heterologous system. This channel subunit retained mechanosensitivity when expressed alone or coexpressed with a beta(2) calcium channel subunit in HEK-293 or Chinese hamster ovary cells. The heterologously expressed human cardiac alpha(1C) splice form also demonstrated mechanosensitivity. Inhibition of kinase signaling did not affect mechanosensitivity of the native channel. Truncation of the alpha(1C) COOH terminus, which contains an inhibitory domain and a proline-rich domain thought to mediate mechanosensitive signaling from integrins, did not disrupt mechanosensitivity of the expressed channel. These data demonstrate mechanical regulation of calcium entry through molecularly identified L-type calcium channels in mammalian cells and suggest that the mechanosensitivity resides within the pore forming alpha(1C)-subunit.