SODIUM AND POTASSIUM CURRENT IN NEONATAL RAT CAROTID-BODY CELLS FOLLOWING CHRONIC IN-VIVO HYPOXIA

Chronic hypoxic acclimatization modifies ventilatory reflexes arising from carotid body stimulation. To explore this, the effects of in vivo chronic hypoxia on membrane currents were quantified in chemoreceptiv e carotid body glomus cells. Pregnant rats were maintained in either n ormoxia (NORM: inspired oxygen tension 141 mmHg), or hypoxia (CHX: ins pired oxygen tension 80 mmHg) from day 3 of gestation, to day 5-10 pos tpartum. Whole cell patch clamp recordings were then made from the mec hanically and enzymatically dissociated carotid body glomus cells of t he rat pups (NORM: 41 cells, CHX: 36 cells) and comparisons of means /- S.E.M. were made with unpaired t-tests. Glomus cells were bright un der phase contrast illumination, formed clusters, were histochemically positive for catecholamines and possessed voltage-gated potassium cur rents that were depressed by acute hypoxia. Acclimatization to chronic hypoxia did not affect rat pup whole body mass (CHX: 12.0 +/- 0.7 g v s. NORM: 11.0 +/- 0.2 g), but it significantly increased blood hematoc rit (CHX: 48.7 +/- 0.9% vs. NORM: 37.8 +/- 0.5%, P < 0.05). Sodium cur rent was not uniformly present in glomus cells from either group, but sodium current was observed in a greater proportion of glomus cells is olated from the chronically hypoxic pups (CHX: 72% vs. NORM: 46%, P < 0.05). The mean peak tetrodotoxin-sensitive sodium current evoked by - 70 mV to +10 mV depolarizations was greater after hypoxic acclimatizat ion (CHX: -100 +/- 25 pA vs. NORM: -38 +/- 15 pA, P < 0.05), but the s odium current density (pA/pF) was unchanged. in contrast, the mean pea k voltage-gated potassium current (pA) evoked by -70 mV to 0 mV depola rizations was unchanged by acclimatization, but the potassium current density (pA/pF) was reduced (P < 0.05). Unchanged sodium current densi ty coupled with decreased potassium current density may make glomus ce lls more excitable during exposure to chronic in vivo hypoxia.