Inositol 1,4,5-trisphosphate is an intracellular second messenger, produced upon stimulation of the phosphoinositide system, capable of mobilizing calcium from intracellular stores. We have recently identified high levels of specific binding sites for inositol 1,4,5-trisphosphate in brain membranes (Worley, P. F., Baraban, J. M., Colvin, J. S., and Snyder, S. H. (1987) Nature 325, 159-161) and have now further characterized these sites. In cerebellar membranes, inositol 1,4,5-trisphosphate binding sites are abundant (20 pmol/mg protein) and display high affinity and selectivity for inositol 1,4,5-trisphosphate (KD approximately equal to 40 nM), whereas other inositol phosphates such as inositol 1,3,4,5-tetrakisphosphate (Ki approximately equal to 10 microM) and inositol 1,4-bisphosphate (Ki approximately equal to 10 microM) exhibit much lower affinity for this site. Submicromolar concentrations of calcium strongly inhibit inositol 1,4,5-trisphosphate binding (IC50 approximately equal to 300 nM). A sharp increase in binding occurs at slightly alkaline pH. These results suggest that actions of inositol 1,4,5-trisphosphate are regulated by physiological alterations in intracellular pH and calcium concentrations.
Based on chemical analyses of some 2 000 rainwater samples, the relation between the pH and the total amount of acid or of base respectively is studied. Considering the carbon dioxide-water system the theoretical relation between pH and total amount of acid or bicarbonate is calculated. A regular deviation is observed between the empirically found and theoretically calculated relation. Starting from chemical analyses of the most important compounds in atmospheric precipitation, a quantitative hypothesis is formulated of how these compounds originally were associated with acids or bases. It is further assumed that these have netralized each other and that the system has come to an equilibrium with the carbon dioxide pressure of the atmosphere. Good agreement is obtained between the predicted amount of acid or base and the measured one, and this is taken as a clear indication of the validity of the model. This model on the stoichiometric relation between acids and bases turns out to be a useful tool both for an interpretation of the amount of acid found in precipitation and in estimating future deposition of acid by precipitation. DOI: 10.1111/j.2153-3490.1972.tb01581.x
The intracellular pH (pHi) of isolated human peripheral blood neutrophils was measured from the fluorescence of 6-carboxyfluorescein (6-CF) and from the equilibrium distribution of [14C]5,5- dimethyloxazolidine -2,4-dione (DMO). At an extracellular pH (pHo) of 7.40 in nominally CO2-free medium, the steady state pHi using either indicator was approximately 7.25. When pHo was suddenly raised from 7.40 to 8.40 in the nominal absence of CO2, pHi slowly rose by approximately 0.35 during the subsequent hour. A change of similar magnitude in the opposite direction occurred when pHo was reduced to 6.40. Both changes were reversible. Intrinsic intracellular buffering power, determined by using graded pulses of CO2 or NH4Cl, was approximately 50 mM/pH over the pHi range of 6.8-7.9. The course of pHi obtained from the distribution of DMO was followed during and after imposition of intracellular acid and alkaline loads. Intracellular acidification was brought about either by exposing cells to 18% CO2 or by prepulsing with 30 mM NH4Cl, while pHo was maintained at 7.40. In both instances, pHi (6.80 and 6.45, respectively) recovered toward the control value at rates of 0.029 and 0.134 pH/min. These rates were reduced by approximately 90% either by 1 mM amiloride or by replacement of extracellular Na with N-methyl-D-glucamine. Recovery was not affected by 1 mM SITS or by 40 mM alpha-cyano-4-hydroxycinnamate (CHC), which inhibits anion exchange in neutrophils. Therefore, recovery from acid loading is probably due to an exchange of internal H for external Na. Intracellular alkalinization was achieved by exposing the cells to 30 mM NH4Cl or by prepulsing with 18% CO2, both at a constant pHo 7.40. In both instances, pHi, which was 7.65 and 7.76, respectively, recovered to the control value. The recovery rates (0.033 and 0.077 pH/min, respectively) were reduced by 80-90% either by 40 mM CHC or by replacement of extracellular Cl with p-aminohippurate (PAH). SITS, amiloride, and ouabain (0.1 mM) were ineffective.(ABSTRACT TRUNCATED AT 400 WORDS)