Cat Heart Muscle in Vitro

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Abstract
The cells of cat right ventricular papillary muscles were depleted of K and caused to accumulate Na and water by preincubation at 2[long dash]3[degree]C. The time courses of changes in cellular ion content and volume and of the resting membrane potential (Vm) were then followed after abrupt rewarming to 27[long dash]28[degree]C. At physiological external K concentration ([K]o = 5.32 m[image]) recovery of cellular ion and water contents was complete within 30 min, the maximal observable rates of K uptake and Na extrusion ([DELTA]mmol cell ion/ (kg dry weight) (min.)) being 3.4 and 3.6, respectively. The recovery rate was markedly slowed at [K]o = 1.0 1.0 m[image]. Rewarming caused Vm measured in cells at the muscle surface to recover within from < 1 to 9 minutes, but only slight restoration of cellular ion contents ( measured in whole muscles) had occurred after 10 min. Studies of recovery in NaCl-free sucrose Ringer''s solution made it possible to separate the ouabain-insensitive outward diffusion of Na as a salt from a simultaneous ouabain-sensitive Na extrusion which is associated with a net cellular K uptake. A hypothesis consistent with these observations is that rewarming may activate a ouabain-sensitive "electrogenic" mechanism, most probably the net active transport of Na out of the cell, from which net K uptake may then follow passively.