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Substances injected into the vitreous cavity leave the eye partly by diffusion into the flowing aqueous, but sometimes also by other mechanisms. To look for such other mechanisms removing organic cations from the rabbit eye, 5 labeled quaternary ammonium compounds were injected intravitreally, mixed with labeled sucrose. The latter leaves essentially by way of the aqueous only. After predetermined times had elapsed the rabbits were killed, and the radioactivity remaining in each eye was measured after combustion of the dried eye bulb. The anticholinergic drug Emepronium disappeared faster than sucrose but only after a delay of many hours. The main experiments were therefore concerned with the time interval 24-48 h after injection. The N- hexylhomologue of Emepronium ' Cetihex ' and the non-sedative antihistamine Aprobit were not eliminated faster than sucrose during this time interval. Since the molecular weights of these quaternaries are similar to that of sucrose and their free diffusion rate should be similar, the present experiments over a limited time interval have proved the existence of an elimination mechanism (besides aqueous flow) only for Emepronium. Tetramethylammonium and tetraethylammonium disappeared markedly faster than sucrose. Since there is no satisfactory way to take their much lower molecular weight into account, the question of a special system for these cations remains open.

Investigated are rabbit atrial trabeculae (2-4 mm length, 150-800 micrometers diameter). When using a standard microelectrode technique, the action potentials after an intracellular 4-AP and TEA load are prolonged. Only the TEA load significantly diminishes the resting potential of the beating preparations. The typical configuration of the action potential following a period of rest (rapid initial repolarization, secondary depolarization and a late retarded repolarization) is not changed qualitatively. During a repetitive stimulation after a pacing pause the action potentials' restitution is accelerated at 4-AP. After 4-AP and TEA load the secondary depolarization of the first post rest action potential is more accentuated. By reconstructing the post rest action potentials a 4-AP sensitive current is determined. At constant drive this current shows a threshold potential at -40 and a reversal potential at -10 mV. The current is inward directed between -40 and -10 mV and is outward directed at more positive potentials than -10 mV. After a pacing pause the current-voltage relation is shifted to more negative potentials. The 4-AP sensitive current is modelled by consideration of a slow activated (during the action potential) and deactivated (during the pacing pause) conductivity. Processes of accumulation are discussed.