Effects of fluid flow on voltage-dependent calcium channels in rat vascular myocytes: fluid flow as a shear stress and a source of artifacts during patch-clamp studies.

We examined the effects of fluid flow on L-type voltage-dependent Ca(2+) channel (VDCC(L)) currents in rat vascular myocytes using the nystatin perforated patch-clamp technique. The effect of fluid flow on the liquid (bathing solution)-metal (Ag/AgCl ground electrode) junction potential was also studied. With a fluid flow of 0-10 ml/min, changes in the junction potential of up to 5 mV were observed in proportion to the flow rate. Accordingly, fluid flow shifted the current-voltage (I-V) relationship of the recorded VDCC(L) currents in a positive direction. In addition to these shifts, fluid flow also increased the peak VDCC(L) current, suggesting some modulatory role for fluid flow in VDCC(L) currents. The use of a 3-M KCl agar-bridge between the ground electrode and bathing solution abnegated the potential shifts, and fluid flow increased the VDCC(L) currents in a voltage-independent manner. These results suggest that the bathing fluid flow can be both a source of erroneous voltage shift between liquid and metal junctions in the patch-clamp configuration and an important shear stress for the cells. The facilitation of VDCC(L) currents by fluid flow in vascular myocytes may contribute to the myogenic contraction of blood vessels. The mechanism by which fluid flow causes the voltage shift is vigorously discussed.