Suppression of L-type Ca 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 (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 (∼16.3 dyne/cm²) 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 ∼34% in the control conditions while increasing I_Ca significantly less (by ∼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 μM), which blocks 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 I_Ca in the presence of FP is at least partly caused by intracellular acidosis via activation of Cl⁻–OH⁻ exchange in rat ventricular myocytes.