ABSTRACT
A system is described for automatic feedback control of plasma potassium concentration in experimental animals. Plasma potassium was monitored continuously and the signal compared with the desired plasma potassium concentration. The resulting error signal controlled the infusion rates of a concentrated potassium chloride solution (50 or 200 mmol litre-1) and a solution of 50% glucose with insulin 200 u litre-1. Plasma potassium was increased or decreased to the desired concentration at various rates, dictated by the controller constants. Increases were achieved significantly faster than reductions. The system may prove useful for elucidating the fate of infused potassium and for determining the optimum rate of insulin infusion in hyperkalaemia. If adapted for clinical use, it may find applications in the management of various abnormalities of potassium homeostasis.
Subject(s)
Microcomputers , Potassium Chloride/administration & dosage , Potassium/blood , Animals , Dogs , Electronics, Medical , Feedback , Infusions, Intravenous , Insulin/administration & dosageABSTRACT
Site-directed mutagenic replacement of M subunit Leu214 by His in the photosynthetic reaction center (RC) from Rhodobacter sphaeroides results in incorporation of a bacteriochlorophyll molecule (BChl) in place of the native bacteriopheophytin (BPh) electron acceptor. Evidence supporting this conclusion includes the ground-state absorption spectrum of the (M)L214H mutant, pigment and metal analyses, and time-resolved optical experiments. The genetically modified RC supports transmembrane charge separation from the photoexcited BChl dimer to the primary quinone through the new BChl molecule, but with a reduced quantum yield of 60 percent (compared to 100 percent in wild-type RCs). These results have important implications for the mechanism of charge separation in the RC, and rationalize the choice of (bacterio)pheophytins as electron acceptors in a variety of photosynthetic systems.
