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This paper describes a procedure of cellular dissociation which allows the isolation of single cells from the human heart while preserving their integrity and physiological function necessary for electrophysiological studies in vitro. During open heart surgery, biopsies were obtained from the right atrium of the beating heart in 16 patients immediately before starting the extracorporeal circulation. The tissue was immediately placed in a cardioplegic solution at 4 degrees, and subsequently in a free-calcium solution at 20 degrees from 20' to 30'. It was then exposed to the proteolytic action of Collagenase type I and Protease type VII (Sigma Chemical Co., St Louis, USA) at 35 degrees for a maximum of 5 hours. The cells were finally transferred into a Tyrode solution at room temperature. With this method we obtained up to 70% of intact human myocytes, 40% of which calcium-tolerant. The subsequent electrophysiological studies performed showed that the cells maintained their morphological and physiological properties.

Several mucolytic agents were evaluated on sputum for testing their viscolytic activity and the bacterial tollerance to each of them. Proteolytic enzymes (trypsin, pepsin, papain, pancreatin), KJ, and dithiothreitol (or its derivatives) were better tollerated by common respiratory pathogens (H. influenzae, D. pneumoniae, Klebsiella, etc.) than other mucolytic agents, as acetil-cysteine, cisteamine-HCl, tension active substances, mercaptoethanol, and others. The dithiothreitol showed also one of the strongest viscolytic effect and therefore it was selected for the routinary sputum digestion at the concentration 0.1% in PBS pH 7.2. Such a solution was added to sputum specimen in different proportions according to the macroscopic "apparent" viscosity of each specimen. However researches on the comparative viscolytic activity of all the agents hereinafter considered are still in progress.

Some properties of three inhibitory substances produced by as many strains of N. meningitidis have been studied. All these substances appeared to be completely destroyed by proteolytic enzymes (trypsin and pronase) and to be very heat-stable; they were insensitive to ultraviolet light and they were stable pH 2-10; filtration through filters of different porosity (Seitz, Berkefeld, millipore membranes) resulted in loss of the inhibitory effect constantly. On the basis of these results and on their specific action specific action, it is possible to class these substances among bacteriocins ("meningocins") at low molecular weight.