EFFECT OF NITROPRUSSIDE AND ENDOTHELIUM-DERIVED PRODUCTS ON SLOW-TWITCH SKELETAL-MUSCLE FUNCTION IN-VITRO

We tested the hypothesis that the products of endothelial cells alter the force developed by skeletal muscle. Since these products have a ve ry short half-life and are produced in a low concentration, we develop ed a superfused muscle preparation in which the mouse soleus (SOL) was superfused at 10.5 ml/min with Krebs - Henseleit buffer (KH) (27 degr ees C; pH 7.4), gassed with 95% O-2 - 5% CO2. To evaluate this prepara tion, we compared the superfused muscles with muscles submerged in a b ath. Ah muscles were stimulated at 50 Hz for 500 ms once every 30 s. S ubmerged SOL developed 275 +/- 15 mN/mm(2), while the superfused muscl es developed 271 +/- 15 mN/mm(2). Both submerged and superfused SOL co nsistently increased rest tension to a 3-mL bolus of 25 mM caffeine an d decreased developed force when exposed to a 3-mL bolus of 30 mM dipr otonated phosphate (pH 6.4). We then exposed superfused SOL to 3-mL bo lus injections of KH, 1 mu M acetylcholine, 30 mM nitroprusside (a sou rce of nitric oxide), and the supernatant from dishes of cultured endo thelial cells from rabbit aorta challenged with acetylcholine. Nitropr usside and the supernatant significantly improved force maintenance, c ompared with KH and acetylcholine, respectively. Since the supernatant should contain products of endothelial cells, these products appear t o have a positive effect on contractile function in slow-twitch skelet al muscle that is similar to the effect of nitric oxide.