Nitric oxide mediates stretch-induced Ca2+ release via activation of phosphatidylinositol 3-kinase-akt pathway in smooth muscle

Background: Hollow smooth muscle organs such as the bladder undergo significant changes in wall tension associated with filling and distension, with attendant changes in muscle tone. Our previous study indicated that stretch induces Ca²⁺ release occurs in the form of Ca²⁺ sparks and Ca²⁺ waves in urinary bladder myocytes. While, the mechanism underlying stretch-induced Ca2+ release in smooth muscle is unknown. Methodology/Principal Findings: We examined the transcluction mechanism linking cell stretch to Ca²⁺ release. The probability and frequency of Ca²⁺ sparks induced by stretch were closely related to the extent of cell extension and the time that the stretch was maintained. Experiments in tissues and single myocytes indicated that mechanical stretch significantly increases the production of nitric oxide (NO) and the amplitude and duration of muscle contraction. Stretch-induced Ca²⁺ sparks and contractility increases were abrogated by the NO inhibitor L-NAME and were also absent in eNOS knockout mice. Furthermore, exposure of eNOS null mice to exogenously generated NO induced Ca²⁺ sparks. The soluble guanylyl cyclase inhibitor ODQ did not inhibit SICR, but this process was effectively blocked by the PI3 kinase inhibitors LY494002 and wortmannin; the phosphorylation of Akt and eNOS were up-regulated by 204±28.6% and 258±30.8% by stretch, respectively. Moreover, stretch significantly increased the eNOS protein expression level. Conclusions/Significance: Taking together, these results suggest that stretch-induced Ca2+ release is NO dependent, resulting from the activation of PI3/Akt pathway in smooth muscle.