Stretch-Induced Increases in Intracellular Ca Stimulate Thick Ascending Limb O 2 - Production and Are Enhanced in Dahl Salt-Sensitive Rats.

Mechanical stretch raises intracellular Ca (Ca-i) in many cell types. Luminal flow-derived stretch stimulates O-2(-) production by thick ascending limbs (THALs). Renal O-2(-) is greater in Dahl salt-sensitive (SS) than salt-resistant (SR) rats. We hypothesized that mechanical stretch stimulates Ca influx via TRPV4 (transient receptor potential vanilloid type 4) which in turn raises Ca-i in THALs; these increases in Ca-i are necessary for stretch to augment O-2(-) production; and stretch-stimulated, and therefore flow-induced, O-2(-) production is enhanced in SS compared with SR THALs due to elevated Ca influx and increased Ca-i. Ca-i and O-2(-) were measured in SS and SR THALs from rats on normal salt using Fura2-acetoxymethyl ester and dihydroethidium, respectively. Stretch raised Ca-i in SS by 270.4 +/- 48.9 nmol/L and by 123.6 +/- 27.0 nmol/L in SR THALs (P<0.02). Removing extracellular Ca eliminated the increases and differences in Ca-i between strains. Knocking down TRPV4 in SS THALs reduced stretch-induced Ca-i to SR levels (SS: 92.0 +/- 15.9 nmol/L; SR: 123.6 +/- 27.0 nmol/L). RN1734, a TRPV4 inhibitor, blunted stretch-elevated Ca-i by approximate to 75% and approximate to 66% in SS (P<0.03) and SR (P<0.04), respectively. Stretch augmented O-2(-) production by 58.6 +/- 10.2 arbitrary fluorescent units/min in SS and by 24.4 +/- 2.6 arbitrary fluorescent units/min in SR THALs (P<0.05). Removal of extracellular Ca blunted stretch-induced increases in O-2(-) and eliminated differences between strains. RN1734 reduced stretch-induced O-2(-) by approximate to 70% in SS (P<0.005) and approximate to 60% in SR (P<0.01). Conclusions are as follows: (1) stretch activates TRPV4, which raises Ca-i in THALs; (2) the increase in Ca-i stimulates O-2(-) production; and (3) stretch-induced O-2(-) production is enhanced in SS THALs due to greater increases in Ca-i.