Suppression of L-type Ca2+ current by fluid pressure in rat ventricular myocytes: Possible role of Cl−–OH− exchange

The application of fluid pressure (FP) in ventricular myocytes using pressurized fluid flow inhibits L-type Ca2+ current (ICa), with approximately 80% of this effect coming through the enhancement of Ca2+ releases from the sarcoplasmic reticulum. In the present study, we explored the remaining mechanisms for the inhibition of ICa by FP. Since FP significantly increases H+ concentration and H+ is known to inhibit ICa, we examined whether pH regulation plays a role in the inhibitory effect by FP on ICa. A flow of pressurized (∼16.3 dyne/cm2) fluid, identical to that bathing the myocytes, was applied onto single rat ventricular myocytes for which the ICa was monitored using whole-cell patch-clamp under HEPES-buffered conditions. Extracellular application of the alkalizing agent, NH4Cl (20 mM), enhanced ICa by ∼34% in the control conditions while increasing ICa significantly less (by ∼21%) in FP-pretreated myocytes, suggesting an inhibition of the effect of NH4Cl on ICa possibly by FP-induced acidosis. Application of DIDS (4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid, 500 μM), which blocks Cl-–HCO3- exchange but not Cl−–OH− exchange, did not alter the inhibitory effect of FP on ICa. Replacement of external Cl− with aspartate attenuated the inhibitory effect of FP on ICa. In highly Ca2+-buffered cells, where Ca2+-dependent inhibition of ICa was minimized, the external Cl− removal eliminated the inhibitory effect of FP on ICa. These results suggest that the decrease of ICa in the presence of FP is at least partly caused by intracellular acidosis via activation of Cl−–OH− exchange in rat ventricular myocytes.

► Fluid pressure suppresses L-type Ca2+ current partly by increasing Ca2+ release in rat ventricular myocytes.
► We examine a role of pH regulation in the inhibition of L-type Ca2+ current by fluid pressure.
► Fluid pressure reduces the Ca2+ current in part by Cl−–OH− exchange-mediated intracellular acidosis.