Relationship between changes of glomus cell current and neural response of rat carotid body

Abstract

1. Mature rat carotid bodies were harvested and sinus nerve activity was recorded in vitro during superfusion with Ringer saline. Membrane currents of glomus cells were simultaneously recorded using conventional whole cell or perforated-patch whole cell recording. Presumptive glomus cells were identified by the presence of a rapidly activated, voltage-dependent outward current above a threshold of -20 mV. 2. Outward current of presumptive glomus cells was inhibited by tetraethylammonium chloride (TEA) (20 mM) and by verapamil (5-10 microM), consistent with previous studies in which isolated glomus cells were used. Somal capacitance, calculated from the current transient following a step hyperpolarization, was 7.47 +/- 0.54 (SE) pF (n = 52). Membrane resistance for perforated-patch recordings was 820 +/- 187 M omega. 3. In perforated-patch recordings, brief periods of hypoxia (30-45 s) caused a marked increase in nerve activity to 21.6 +/- 2.7 times baseline spiking frequency (n = 59) but no significant change in membrane resistance or outward current. No change in holding current was detected, although the low amplifier gain precluded high-resolution measurement. Similar results were obtained using conventional whole cell recording, except that outward current significantly decreased during hypoxia but failed to recover in the immediate posthypoxia period. 4. TEA (20 mM) rapidly inhibited outward current to 55 +/- 7% (n = 15) of predrug current, but nerve activity only slightly increased to 2.0 +/- 0.3 times baseline spike frequency (n = 15). Brief anoxia (40 s in duration) in the presence of TEA evoked a brisk increase in nerve activity to 30 +/- 13 times baseline frequency (n = 3), demonstrating that organ function was not blocked by TEA. 5. Charybdotoxin (10 nM) significantly reduced outward current by 12.1 +/- 3.0% (n = 11) but did not significantly alter nerve activity, holding current, or membrane resistance. Apamin (100 nM) did not significantly affect nerve activity, membrane resistance, or holding current. Outward current decreased by 11.4 +/- 6.1% (n = 13). 6. These results show a dissociation between changes in glomus cell voltage-gated outward currents and changes in afferent nerve activity. This suggests that modulation of glomus cell K+ current by hypoxia is not the primary step in initiating the nerve response to hypoxia in the rat carotid body.