Flow-dependent chemosensory activity in the carotid body superfused in vitro.

The relationship between carotid body chemoreceptor activity and flow was studied in preparations superfused in vitro. The carotid bodies were excised from pentobarbitone-anesthetized cats and superfused with modified Tyrode's solution, buffered with HEPES-NaOH to pH 7.41. The bath temperature was kept constant at 37.7 degrees C. The frequency of chemosensory discharges from the entire carotid nerve was determined during steady-state superfusion with 100% or 20% O2-equilibrated saline at flow rates between 0.15 and 2.95 ml/min, and during 5 min flow interruptions. The peak frequency evoked by flow interruptions was maximal and independent of previous superfusion flows, but the half-excitation time of chemosensory responses to flow interruption was minimal when preceded by superfusion with 100% O2-equilibrated saline at 0.7 ml/min. In steady-state conditions, mean chemosensory activity was higher at lower rates of flow, and, at constant flow, higher under 20% O2 than under 100% O2. To allow comparisons of all data, basal frequencies at given basal flows were referred to their own maximal frequencies evoked by flow interruptions. The best fitting for the relation between basal chemosensory activity and superfusion flow was provided by inverse sigmoid (logistic decay) curves: r = -0.90 and -0.84, at 100% and 20% O2 levels, respectively. The maximal gains were at about 0.78 and 0.86 ml/min, respectively. It is concluded that the chemosensory discharge frequency recorded from carotid bodies superfused in vitro is determined by the superfusion flow, when all other natural chemoreceptor stimuli are held constant.