NO-sGC Pathway Modulates Ca(2+) Release and Muscle Contraction in Zebrafish Skeletal Muscle

Vertebrate skeletal muscle contraction and relaxation is a complex process that depends on Ca(2+) ions to promote the interaction of actin and myosin. This process can be modulated by nitric oxide (NO), a gas molecule synthesized endogenously by (nitric oxide synthase) NOS isoforms. At nanomolar concentrations NO activates soluble guanylate cyclase (sGC), which in turn activates protein kinase G via conversion of GTP into cyclic GMP. Alternatively, NO post-translationally modifies proteins via S-nitrosylation of the thiol group of cysteine. However, the mechanisms of action of NO on Ca(2+) homeostasis during muscle contraction are not fully understood and we hypothesize that NO exerts its effects on Ca(2+) homeostasis in skeletal muscles mainly through negative modulation of Ca(2+) release and Ca(2+) uptake via the NO-sGC-PKG pathway. To address this, we used 5–7 days-post fecundation-larvae of zebrafish, a well-established animal model for physiological and pathophysiological muscle activity. We evaluated the response of muscle contraction and Ca(2+) transients in presence of SNAP, a NO-donor, or L-NAME, an unspecific NOS blocker in combination with specific blockers of key proteins of Ca(2+) homeostasis. We also evaluate the expression of NOS in combination with dihydropteridine receptor, ryanodine receptor and sarco/endoplasmic reticulum Ca(2+) ATPase. We concluded that endogenous NO reduced force production through negative modulation of Ca(2+) transients via the NO-sGC pathway. This effect could be reversed using an unspecific NOS blocker or sGC blocker.