The application of fluid pressure (FP) in ventricular myocytes using pressurized fluid flow inhibits L-type Ca2+ current (I-Ca), 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 I-Ca by FP. Since FP significantly increases H+ concentration and H+ is known to inhibit I-Ca, we examined whether pH regulation plays a role in the inhibitory effect by FP on I-Ca. A flow of pressurized (similar to 16.3 dyne/cm(2)) fluid, identical to that bathing the myocytes, was applied onto single rat ventricular myocytes for which the I-Ca was monitored using whole-cell patch-clamp under HEPES-buffered conditions. Extracellular application of the alkalizing agent, NH4Cl (20 mM), enhanced I-Ca by similar to 34% in the control conditions while increasing I-Ca significantly less (by similar to 21%) in FP-pretreated myocytes, suggesting an inhibition of the effect of NH4Cl on I-Ca possibly by FP-induced acidosis. Application of DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid, 500 mu M), which blocks Cl--HCO3- exchange but not Cl--OH- exchange, did not alter the inhibitory effect of FP on I-Ca. Replacement of external Cl- with aspartate attenuated the inhibitory effect of FP on I-Ca. In highly Ca2+-buffered cells, where Ca2+-dependent inhibition of I-Ca was minimized, the external Cl- removal eliminated the inhibitory effect of FP on I-Ca. These results suggest that the decrease of lc, in the presence of FP is at least partly caused by intracellular acidosis via activation of Cl--OH- exchange in rat ventricular myocytes. (C) 2011 Elsevier Inc. All rights reserved.