Uptake kinetics and ion requirements for extraneuronal uptake of noradrenaline by arterial smooth muscle and collagen.

Abstract

1. The ionic requirements for noradrenaline uptake into vascular smooth muscle cells were studied by perfusing rabbit isolated ear arteries with noradrenaline (10(-3)M) either in Krebs solution or in Krebs solution modified by altering the concentration of one or more ion. Noradrenaline uptake was measured by quantitative microphotometry.2. Some uptake into smooth muscle continued in isotonic sucrose in the absence of all ions. Omission of Na(+) from the Krebs solution partially inhibited uptake as did high (100 mM) K(+). Omission of K(+), Ca(++) or Mg(++) had no effect on uptake. Lithium was able completely to substitute for Na(+).3. Alteration in ion concentration did not affect the binding of noradrenaline to collagen.4. The kinetics of uptake of noradrenaline into smooth muscle were analysed and found to be saturable with a Km of 4.9 x 10(-4)M.5. It is concluded that the ionic requirements of the transport mechanism for the uptake of noradrenaline by vascular smooth muscle show a relatively low specificity.