Fluid flow-induced increase in inward Ba2+ current expressed in HEK293 cells transiently transfected with human neuronal L-type Ca2+ channels

Abstract

Mechanical forces can alter the gating of several kinds of ion channels in many types of cells, but the mechanisms underlying the mechanosensitivity are not clearly understood. To date, there are very few reports on mechanosensitivity of Ca2+ channels, particularly neuronal Ca2+ channels. We examined the mechanical sensitivity of human recombinant L-type Ca2+ channels in response to fluid flow. Neuronal L-type Ca2+ channels (Ca(v) 1.2) were expressed transiently in HEK293 cells using expression cDNA clones of human alpha1C, alpha2delta, and beta subunits along with green fluorescent protein (GFP) as a reporter protein. Current (I(Ba)) through these heterologously-expressed channels was measured using whole cell recording technique with 20 mM Ba2+ as charge carrier. Transfected cells were exposed to a constant, increased fluid flow from a separate pipette during current recording. The L-type I(Ba) was found to be very sensitive to the flow-induced shear forces. Peak current amplitude increased by as much as approximately 50% during fluid flow as compared to that in the absence of fluid pressure. However, no change was observed in the amplitude of the average current during the final 5 ms of the 150-ms voltage step. Current amplitude promptly returned to normal control levels upon stopping fluid flow. The current-voltage relationship was not altered by fluid flow. The flow-induced increase in current amplitude exhibited an apparent shift in steady-state inactivation toward more negative potentials; inactivation was faster but was not voltage dependent. Activation was slightly faster under flow. Thus, increased mechanical tension associated with fluid flow can alter the fundamental properties of voltage-gated Ca2+ channels, even for channels which might not normally be exposed to fluid flow shear forces in their native environment.