Kinetic Studies of Calcium Distribution in Ventricular Muscle of the Dog

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Abstract
Five phases (0 to 4) were defined kinetically for calcium in the dog papillary muscle vascularly perfused for five to six hours with perfusate containing 5 mM/liter calcium. The mean rate constant, λ, (min-1), approximate calcium concentration (mM/liter muscle water) and suggested origin of each phase are respectively: (0) λ0 = 3.5, 0.4, vascular; (1) λ1 = 0.59, 1.8, interstitial; (2) λ2 = 0.116, 1.7, "specialized" calcium transport system (?sarcoplasmic reticulum); (3) λ3 = 0.021, 2.0, intracellular; (4) λ approx 0.004, ++ content of the "specialized system" represented by phase 2 is controlled by movements of Na+ into and out of this system is discussed. Ca++ movements associated with increased frequency of contraction are also discussed in the context of their possible relation to Na+ exchange.