Combined Effects Of Nitrate And Caffeine On Contractions Of Skeletal Muscles
Joint action of 1 mm caffeine and NO3– after exposure to NO3– alone did not increase tension output of excised, curarized gastrocnemius muscles of healthy mice beyond NO3– values. In dystrophic mouse muscles, twitch tension increased further and 1.5 times as much as in 1 mm caffeine alone. In both muscles caffeine pretreatment permitted NO3– further to enhance twitch tension as though it were acting alone. Caffeine enhancement of tetanus tension disappeared in normal and rose further in dystrophic muscles. In both muscles jointly evoked maximal twitch tensions were the same regardless of pretreatment. Neither agent alone could duplicate jointly elicited tension increases. In excised, curarized frog sartorius muscles jointly produced twitch tensions after NO3– pretreatment were the sum of individual NO3– and caffeine enhancements. Caffeine pretreatment reduced the subsequent NO3– alone. These results suggest defects in NO3–-susceptible Ca++ sites of dystrophic membranes, and greater sensitivity to caffeine-induced Ca++ mobility in frog than in mouse muscles.