EFFECT OF PROPRANOLOL ON RAT-BRAIN SYNAPTOSOMAL NA-K+-ATPASE, MG2+-ATPASE AND CA2+-ATPASE()

The beta blocker drug propranolol (PPL) significantly inhibited Na+-K-ATPase, Mg2+-ATPase and Ca2+-ATPase activities in a concentration dep endent manner in rat brain synaptosomes. The concentrations required f or 50% inhibition (IC50) ih the activity of these enzymes were 1.5-1.8 mM. The double-reciprocal plot of ATP-stimulated Na+-K+-ATPase activi ty in the presence of PPL showed apparent decrease in K-m and V-max an d the inhibition was of an uncompetitive type with respect to ATP. The nature of inhibition by PPL of Na+-activated Na+-K+-ATPase activity w as of a mixed type showing an increase in K-m and decrease in V-max. P otassium activation kinetics of Na+-K+-ATPase displayed uncompetitive type of inhibition with PPL since K-m and V-max were decreased. Magnes ium activation of Mg2+-ATPase showed decrease in V-max with no apparen t change in K-m in the presence of PPL. The drug inhibited synaptosoma l Ca2+-ATPase in an uncompetitive manner. The observed inhibition of s ynaptosomal ATPases indicates possible alterations In the synaptic tra nsmission by the beta blocker drug PPL. (C) 1997 Elsevier Science Irel and Ltd.