Inoculum-dependent division lag of Bacillus cultures and its relation to an endogenous factor(s) ("schizokinen")

Lankford, C. E. (The University of Texas, Austin), James R. Walker, James B. Reeves, N. H. Nabbut, B. R. Byers, and R. J. Jones. Inoculum-dependent division lag of Bacillus cultures and its relation to an endogenous factor(s) ("schizokinen"). J. Bacteriol. 91:1070-1079. 1966.-When cells of Bacillus megaterium, grown on Brain Heart Infusion Agar, were inoculated into a chemically defined medium, they exhibited a division lag which was an inverse function of inoculum size. The addition of filtrates of cultures from the same medium eliminated the inoculum-dependent component of lag, but not an inoculum-independent residual lag of constant duration. Culture filtrate of B. subtilis var. niger not only eliminated its inoculum-dependent lag but also was required to sustain exponential division. Dose-response and "growth time" bioassays, developed to measure lag-reducing activity of filtrates, demonstrated accumulation of active filtrate factor to a "critical" concentration prior to division initiation. Addition of this concentration to cultures eliminated the inoculum-dependent lag. Accumulation of the factor ceased temporarily at onset of division, but excretion was resumed later during exponential growth. Accumulation of a lag-reducing, cell-associated factor followed a similar course. Chromatographic and bioautographic analyses of culture filtrates of B. megaterium indicated that a single substance was primarily responsible for their activity. Results of dose-response tests for reciprocal activities of filtrates of different Bacillus species and strains suggested production of different factors by some, and of different quantities of similar factors by others. It is proposed that such endogenous factors which are synthesized and accumulate to a population-dependent concentration as a requisite to initiation and maintenance of division be designated as "schizokinens."     

Cl− channels in basolateral renal medullary memnbranes: III. Determinants of single-channel activity

Summary We evaluated the effects of vawrying aqueous Cl^– concentrations, and of the arginyl- and lysyl-specific reagent phenylglyoxal (PGO), on the properties of Cl^– channels fused from basolaterally enriched renal medullary vesicles into planar lipid bilayers. The major channel properties studied were the anion selectivity sequence, anionic requirements for, channel activity. and the efects of varying Cl^– concentrations and/or PGO on the relation between holding voltageV _H -mV) and open-time probability (P _o).Reducingcis Cl^– concentrations, in the range 50–320mm, produced a linear reduction in fractional open time (P _v) with a half-maximal reduction inP _o atcis Cl^–170mM. Channel activity was sustained by equimolar replacement ofcis Cl^– with F^–, but not with impermeant isethionate. Fortrans solutions, the relation between Cl^– concentration andP ₀ at 10mm Cl^–. Reducingcis Cl^– had no effect on the gating charge (Z) for channel opening, but altered significantly the voltage-independent, energy (G) for channel opening.Phenylglyoxal (PGO) reducedZ and altered G for Cl^– channel activity when added tocis, but nottrans solutions, Furthermore, in the presence ofcis PGO, reducing thecis Cl^– concentration had no effect onZ but altered G. Thus we propose thatcis PGO and,cis Cl^– concentrations affect separate sites determining channel activity at the extracellular faces of, these Cl^– channels.     

Cl− transport in basolateral renal medullary vesicles: II. Cl− channels in planar lipid bilayers

Summary The present studies examined some of the properties of Cl^– channels in renal outer medullary membrane vesicles incorporated into planar lipid bilayers. The predominant channel was anion selective having aP _Cl/P _K ratio of 10 and a unit conductance of 93 pS in symmetric 320mm KCl. In asymmetric KCl solutions, theI-V relations conformed to the Goldman-Hodgkin-Katz equation. Channel activity was voltage-dependent with a gating charge of unity. This voltage dependence of channel activity may account, at least in part, for the striking voltage dependence of the basolateral membrane Cl^– conductance of isolated medullary thick ascending limb segments. The Cl^– channels incorporated into the planar bilayers were asymmetrical: thetrans surface was sensitive to changes in ionized Ca²⁺ concentrations and insensitive to reducing KCl concentrations to 10mm, while thecis side was insensitive to changes in ionized Ca²⁺ concentrations, but was inactivated by reducing KCl concentrations to 50mm.