PERTUSSIS TOXIN INHIBITS NORADRENALINE ACCUMULATION BY BOVINE ADRENAL-MEDULLARY CHROMAFFIN CELLS

Bovine adrenal medullary chromaffin cells maintained in tissue culture accumulated [H-3]-noradrenaline by a high affinity, Na+-dependent, desipramine-sensitive process. The accumulation was linear with time (1-90min) and had an apparent K(m) of 0.52+/-0.24 mumol/l and V(max) of 1.70+/-0.48 pmol/(10(5) cells.15 min). Pretreatment of the cells with the ADP-ribosylating agent pertussis toxin resulted in a reduction in the V(max) [0.81+/-0.39 pmol/(10(5) cells.15 min)] but no significant change in the apparent affinity (K(m) = 0.42+/-0.07 mumol/l). This inhibition of [H-3]noradrenaline accumulation was distinct from that produced by the vesicular transport inhibitor reserpine. Pertussis toxin inhibition probably did not arise through an indirect action on the Na+-gradient because while, as expected, Na+,K+-ATPase inhibition reduced [H-3]noradrenaline accumulation, pertussis toxin pretreatment always caused a further significant reduction even in the presence of maximally effective concentrations of ouabain. Stimulation of the cAMP-protein kinase A system by forskolin or 8-bromocyclic AMP also caused a reduction in [H-3] noradrenaline accumulation but again pertussis toxin pretreatment always resulted in a further reduction. Thus, the data provide evidence for a pertussis toxin-sensitive element in the catecholamine accumulation process and are consistent with an action at a site directly associated with the transporter itself rather than with an indirect action via secondary processes.