Fluid pressure modulates L-type Ca²⁺ channel via enhancement of Ca²⁺-induced Ca²⁺ release in rat ventricular myocytes

Abstract

This study examines whether fluid pressure (FP) modulates the L-type Ca(2+) channel in cardiomyocytes and investigates the underlying cellular mechanism(s) involved. A flow of pressurized (approximately 16 dyn/cm(2)) fluid, identical to that bathing the myocytes, was applied onto single rat ventricular myocytes using a microperfusion method. The Ca(2+) current (I(Ca)) and cytosolic Ca(2+) signals were measured using a whole cell patch-clamp and confocal imaging, respectively. It was found that the FP reversibly suppressed I(Ca) (by 25%) without altering the current-voltage relationships, and it accelerated the inactivation of I(Ca). The level of I(Ca) suppression by FP depended on the level and duration of pressure. The Ba(2+) current through the Ca(2+) channel was only slightly decreased by the FP (5%), suggesting an indirect inhibition of the Ca(2+) channel during FP stimulation. The cytosolic Ca(2+) transients and the basal Ca(2+) in field-stimulated ventricular myocytes were significantly increased by the FP. The effects of the FP on the I(Ca) and on the Ca(2+) transient were resistant to the stretch-activated channel inhibitors, GsMTx-4 and streptomycin. Dialysis of myocytes with high concentrations of BAPTA, the Ca(2+) buffer, eliminated the FP-induced acceleration of I(Ca) inactivation and reduced the inhibitory effect of the FP on I(Ca) by approximately 80%. Ryanodine and thapsigargin, abolishing sarcoplasmic reticulum Ca(2+) release, eliminated the accelerating effect of FP on the I(Ca) inactivation, and they reduced the inhibitory effect of FP on the I(Ca). These results suggest that the fluid pressure indirectly suppresses the Ca(2+) channel by enhancing the Ca(2+)-induced intracellular Ca(2+) release in rat ventricular myocytes.

Axial Stretch of Rat Single Ventricular Cardiomyocytes Causes an Acute and Transient Increase in Ca 2+ Spark Rate

“…Similar deformation-induced increases in Ca 2+ spark rate have been observed in the depth of atrial myocytes during sarcolemmal fluid-jet stimulation 39. Also, RyR2 mechanosensitivity could underlie the fluid-pressure induced increase in Ca 2+ -induced Ca 2+ releasability from the SR, observed in rat ventricular cardiomyocytes 40. Alternatively, there may be mitochondria-mediated responses,39 or currently unknown effects of fast-acting local signal transduction pathways that are relevant for RyR2 function and affected by the cytoskeleton 41…”

Effects of Physical Activity and Inactivity on Muscle Fatigue

“…Animal studies have shown that HIT in rats for 5 weeks results in 30 and 85% in the MCT1 and Na + /bicarbonate transporter, respectively, while MCT4 remained unchanged (Thomas et al, 2007). In humans, changes in the Na + /H + exchanger protein levels by 30% have been reported in the 4-week high-intensity sprint training study of Iaia et al (2008). Moreover, significant increases in MCT1 and Na + /H + exchanger protein densities have been found after HIT, especially when training bouts cause a significant accumulation of H + in the muscle (Mohr et al, 2007).…”

Flow-induced activation of TRPV5 and TRPV6 channels stimulates Ca2+-activated K+ channel causing membrane hyperpolarization

“…Fluid flow was gravity driven (25-85 μl/min) to generate shear stresses from 0.34 to 1.15 dyne/cm 2 . The shear pressure was calculated for fluid flow in cylindrical tubes according to the equation as τ = 6μQ/π r 3 , where τ is shear stress or pressure (dyne/cm 2 ), μ represents the fluid viscosity, Q is the flow rate (ml/s), and r is the internal radius of the tube [21]. …”