SUPPRESSION OF GLOMUS CELL K-AMINOPYRIDINE IS NOT RELATED TO [CA2+](I), DOPAMINE RELEASE AND CHEMOSENSORY DISCHARGE FROM CAROTID-BODY( CONDUCTANCE BY 4)

The hypothesis that suppression of O-2-sensitive K+ current is the ini tial event in hypoxic chemotransduction in the carotid body glomus cel ls was tested by using 4-aminopyridine (4-AP), a known suppressant of K+ current, on intracellular [Ca2+](i), dopamine secretion and chemose nsory discharge in cat carotid body (CB). In vitro experiments were pe rformed with superfused-perfused cat CBs, measuring chemosensory disch arge, monitoring dopamine release by microsensors without and with 4-A P (0.2, 1.0 and 2.0 mM in CO2-HCO3- buffer) and recording [Ca2+](i) by ratio fluorometry in isolated cat and rat glomus cells. 4-AP decrease d the chemosensory activities in normoxia but remained the same in hyp oxia and in flow interruption. It decreased the tissue dopamine releas e in normoxia, and showed an additional inhibition with hypoxia. Also, 4-AP did not evoke any rise in [Ca2+](i) in glomus cells either durin g normoxia and hypoxia, although hypoxia stimulated it. Thus, the lack of stimulatory effect on chemosensory discharge; inhibition of dopami ne release and unaltered [Ca2+](i) by 4-AP are not consistent with the implied meaning of the suppressant effect on K+ current of glomus cel ls. (C) 1998 Elsevier Science B.V.