Behavior of Junction Channels Between Rat Glomus Cells During Normoxia and Hypoxia

Abstract

The activity of gap junction channels between cultured and clustered carotid body glomus cells of the rat was studied with dual voltage clamping during normoxia (Po 2 300 Torr) and hypoxia induced by sodium dithionite (Na2S2O4) or 100% N2. Na2S2O4reduced the saline Po 2 to ∼10 Torr, whereas 100% N2 reduced ambient O2 to ∼60 Torr. The following observations were made. 1) In normoxia, the intercellular macroconductance ( G j = 3.0 ± 1.01 ns, mean ± SE) was changed unevenly (increased and decreased) under hypoxic conditions by either agent, although N2 produced the largest changes. 2) The intercellular microconductances of the channels ( g j = 104.44 ± 10.16 pS under normoxic conditions) significantly decreased in 100% N2 but showed depressions and enhancements in Na2S2O4. 3) The conductance of single-junction channels (SChs), calculated as g j variance/mean g j, yielded a mean of ∼17.6 pS. Larger values were obtained with manual measurements of the data (∼34 pS). Hypoxic hypoxia (induced by 100% N2) significantly depressed the conductance of SChs when calculated from digitized records or from manual measurements. Hypoxia induced by Na2S2O4did not significantly change junctional conductance. 4) The number of intercellular channels, calculated as g j/SCh g j, had a mean of ∼452 (range 1 to 2,471). During N2-induced hypoxia, this number significantly decreased to ∼84 but remained unchanged during Na2S2O4hypoxia. 5) The mean open time of junction channels varied from 4 to 30 ms in different experiments, having an overall mean of μ = 11.33 ± 0.33 ms. This value was significantly reduced by 100% N2 but was not changed by Na2S2O4. 6) Intracellular calcium ([Ca2+]i), 46.2 ± 4.84 nM under normoxia, significantly increased to 77.32 ± 11.27 nM with Na2S2O4and to 66.39 ± 11.64 nM with 100% N2. It is concluded that 100% N2 uncouples glomus cells by significantly reducing intercellular macro- and microconductances. Hypoxia induced by Na2S2O4had variable effects. The coupling effects of hypoxia may depend on, or be aided by, increases in [Ca2+]i and/or intracellular pH changes. However, secreted transmitters and ATP plus the effects of hypoxia on second messengers and other cytoplasmic components may also play an important role in this phenomenon.