Modulation of junctional conductance between rat carotid body glomus cells by hypoxia, cAMP and acidity

Abstract

Short-term cultures of glomus cells (up to seven days), were employed to study intercellular electrical communications. Bidirectional electric coupling was established under current clamping after impaling two adjacent glomus cells with microelectrodes, and alternate stimulation and recording. Their resting potential ( V m) and input resistance ( R o) were thus measured. Both coupled cells were then voltage clamped at a level between their V ms. Current pulses applied to either cell elicited a transjunctional voltage ( V j) and current ( I j), used to calculate the junctional conductance ( G j). G j was 1.52±0.29 nS (mean±S.E.; n=147). V j linearly influenced G j, suggesting ohmic junctions. G j was not affected by V m in 50% of the cases. However, there was V m-dependence in the others, but voltage changes had to be large (>±40 mV from the V m). Therefore, physiologically or pharmacologically induced glomus cell depolarization or hyperpolarization may not significantly affect intercellular coupling unless there are large variations in V m. Hypoxia (induced by Na 2S 2O 4 1 mM or 100% N 2) decreased G j in 60–80% of the pairs while producing tighter coupling in the rest. Similar effects were obtained when the medium was acidified with lactic acid 1–10 mM. Cobalt chloride (3 mM) prevented, diminished or reversed the changes in G j observed during low PO 2, suggesting that [Ca 2+] i changes are important in hypoxic uncoupling. However, non-specific cationic effects of Co 2+ have not been ruled out. Applications of the membrane-permeant dB-cAMP 1 mM tightened coupling in almost all cell pairs. This is important because endogenous cAMP increases during hypoxia. Our results suggest that multiple factors modulate junctional conductance between glomus cells. Changes in G j by `natural' stimuli and/or cAMP may play an important role in chemoreception, especially in titrating the release of transmitters toward the carotid nerve terminals.