EFFECTS OF ALBUMIN SENSITIZATION AND CHALLENGE OF GUINEA-PIGS ON UPTAKE(2) OF ISOPRENALINE IN TRACHEALIS MUSCLE

There is evidence that hyperpolarization of cells by various mechanism s results in stimulation of uptake(2) of catecholamines and, conversel y, that depolarization causes inhibition of uptake(2). The aim of this study was to examine whether changes that have been shown to occur in the resting membrane potential of the trachealis muscle of guinea pig s that have been sensitized to albumin (hyperpolarization) or albumin- sensitized followed by inhalational albumin challenge (depolarization) are reflected in changes in uptake(2) in the smooth muscle. Uptake(2) of isoprenaline (as measured by the steady-state rate of specific H-3 -O-methylisoprenaline formation normalized for the isoprenaline concen tration) was determined in isolated segments of trachealis muscle that were incubated in H-3-(+/-)-isoprenaline and were from guinea pigs fr om three treatment groups: (i) controls, (ii) albumin-sensitized and ( iii) albumin-sensitized and challenged. At an isoprenaline concentrati on that does not hyperpolarize the trachealis muscle (1 nmol/l), uptak e(2) was significantly greater in the muscle from sensitized guinea pi gs than that from control or sensitized and challenged guinea pigs. Wh en a drug that hyperpolarized the trachealis muscle was present (25 nm ol/l isoprenaline or 10 mu mol/l (-)-cromakalim), there were no differ ences in uptake, between the three groups. Propranolol prevented the s timulation of uptake(2) by isoprenaline and glibenclamide prevented st imulation of uptake, by (-)-cromakalim. In the presence of propranolol or glibenclamide, there were no differences in uptake(2) between the three treatment groups of guinea pigs. It is concluded from these resu lts that uptake(2) of isoprenaline in the trachealis muscle appears to reflect the resting membrane potential in albumin-sensitized guinea p igs, whether they were also albumin challenged or not, but these diffe rences are not maintained in the presence of drugs that change the mem brane potential.