PROPERTIES OF IONIC CURRENTS FROM ISOLATED ADULT-RAT CAROTID-BODY CHEMORECEPTOR CELLS - EFFECT OF HYPOXIA

1. The electrical properties of chemoreceptor cells from neonatal rat and adult rabbit carotid bodies (CBs) are strikingly different. These differences have been suggested to be developmental and/or species rel ated. To distinguish between the two possibilities, the whole-cell con figuration of the patch-clamp technique was used to characterize the i onic currents present in isolated chemoreceptor cells from adult rat C Bs. Since hypoxia-induced inhibition of O-2-sensitive K+ currents is c onsidered a crucial step in O-2 chemoreception, the effect of hypoxia on the adult rat chemoreceptor cell currents was also studied. 2. Outw ard currents were carried mainly by K+, and two different components c ould be distinguished: a Ca2+-dependent K+ current (I-K(Ca)) sensitive to Cd2+ and charybdotoxin (CTX), and a Ca2+-insensitive, voltage-depe ndent K+ current (I-K(V)). I-K(V) showed a slow voltage-dependent acti vation (time constant (tau) of 87.4 ms at -20 mV and 8.8 ms at +60 mV) and a very slow inactivation, described by the sum of two exponential s (tau(1) = 684 +/- 150 ms and tau(2) = 4.96 +/- 0.76 s at +30 mV), th at was almost voltage insensitive. The kinetic and pharmacological pro perties of I-K(V) are typical of a delayed rectifier K+ channel. 3. Vo ltage-dependent Ca2+ currents (I-Ca) were present in nineteen of twent y-seven cells. TTX- Na+ currents were also observed in about 10% of th e cells. 4. Low P-O2 (< 10 mmHg) reduced the whole outward current amp litude by 22.17 +/- 1.96% (n = 27) at +20 mV. This effect was absent i n the presence of Cd2+. Since low P-O2 did not affect I-Ca, we conclud e that hypoxia selectively blocks I-K(Ca). 5. The properties of the cu rrents recorded in adult rat chemoreceptor cells, including the specif ic inhibition of I-K(Ca) by hypoxia, are similar to those reported in neonatal rat CB cells, implying that the differences between rat and r abbit chemoreceptor cells are species related.