The emergence of drug delivery using water stable metal-organic frameworks has elicited a lot of interest in their biocompatibility. However, few studies have been conducted on their stability in common buffers, cell media, and blood proteins. For these studies, single crystal ZIF-8 approximately 1 um in diameter were synthesized, incubated with common laboratory buffers, cell media, and serum, and then characterized by PXRD, IR, DLS, and SEM. Time-resolved SEM and PXRD demonstrate that buffers containing phosphate and bicarbonate alter the appearance and composition of ZIF-8; however, cargo inside the ZIF-8 does not appear to leak out, in most of these buffers, even when the ZIF-8 itself is displaced by phosphates. On the other hand, blood proteins in serum dissolve ZIF-8, causing trapped biomolecules to escape. The study presented here suggests that ZIF-8 can undergo dramatic surface chemistry changes that may affect the interpretation of cellular uptake and cargo release data. On the other hand, it provides a rational explanation as to how ZIF-8 neatly dissolves in vivo.
In order to characterize differences in mating types in Euplotes vannus, two cell populations of complementary mating types were mixed and exposed to a pattern of irritation (switching schedule of agitation and rest). Cells costimulate each other, as is seen from courtship behavior during still intervals, but do not pair. Prolonged periods of treatment cause distinctly reduced cell interactions. After 72 hr they have ceased completely: Overstimulated cells have lost their ability to conjugate. However, with fresh cells of mating types, which are different from both constituents of the mixture, overstimulated cells mate normally as judged by time course, cycloheximide‐sensitivity, and concanavalin A (ConA) binding. Conjugation competence thus is selectively lost only for that mating type which has been the partner in the perturbated mixture. The required classification of pairs with regard to mating‐type combinations were confirmed by several identification procedures using amicronucleates and doublets. The observed phenomena during the mating‐type‐specific loss of conjugation ability are consistent with the concept that this is due to a physiological disappearance of a specific mating substance, which might correspond to the receptor side of the extended gamone‐receptor hypothesis of Miyake ('81).
Co-stimulation of mixed complementary mating types of Euplotes vannus was blocked if [K+]o was raised to at least 60 mmol]−1. This inhibition could be cancelled by simultaneously raising [Ca2+]o. An electrophysiological investigation showed that elevation of either [K+]o or [Ca2+]o depolarized the cell. The effect of potassium was observed at concentrations above 50 mmol l−1, with a slope of about 38 mV/decade change, and was accompanied by a reduction in membrane resistance. Calcium had an effect at lower concentrations than potassium, but the slope was lower, and was associated with a rise in resistance. When potassium and calcium were applied together in ratios at which the calcium level was just sufficient to annul the K+-induced block of conjugation, the membrane was depolarized only slightly more than in potassium alone, and resting resistance was near the control level. It is therefore proposed that high [K+]o blocks co-stimulation by acting upon membrane resting conductance.
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