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 Ca²⁺ 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.