Abstract
Substrate stiffness is crucial for diverse cell functions, but the mechanisms conferring cells with mechanosensitivity are still elusive. By tailoring substrate stiffness with 10-fold difference, we showed that L-type voltage-gated Ca(2+) channel current density was greater in chick ventricular myocytes cultured on the stiff substrate than on the soft substrate. Blockage of the BK channel increased the Ca(2+) current density on the soft substrate and consequently eliminated substrate stiffness regulation of the Ca(2+) channel. The expression of the BK channel, including the STREX-containing α-subunit that forms stretch-activated BK channel in myocytes and the BK channel function in myocytes (and also in HEK293 cells heterologously expressing STREX-containing α- and β(1)-subunits) was reduced in cells cultured on the stiff substrate. Furthermore, in HEK293 cells coexpressing the cardiac Ca(V)1.2 channel and STREX-containing BK channel, the Ca(2+) current density was greater in cells on the stiff substrate, which was not observed in cells expressing the Ca(V)1.2 channel alone or coexpressing with the STREX-deleted BK channel. These results provide strong evidence to show that the stretch-activated BK channel plays a key role in functional regulation of cardiac voltage-gated Ca(2+) channel by substrate stiffness, revealing, to our knowledge, a novel mechanosensing mechanism in ventricular myocytes.