The Journal of Neurophysiology Vol. 88 No. 2 August 2002, pp. 639-649
Copyright ©2002 by the American Physiological Society

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

 ¹Department of Physiology, University of Utah School of Medicine, Salt Lake City, Utah 84108-1297; and  ²Department of Physiology, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay

Abudara, Verónica, R. G. Jiang, and C. Eyzaguirre. Behavior of Junction Channels Between Rat Glomus Cells During Normoxia and Hypoxia. J. Neurophysiol. 88: 639-649, 2002. 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 (PO₂ 300 Torr) and hypoxia induced by sodium dithionite (Na₂S₂O₄) or 100% N₂. Na₂S₂O₄ reduced the saline PO₂ 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 Na₂S₂O₄ did 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 Na₂S₂O₄ hypoxia. 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 Na₂S₂O₄ and 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 Na₂S₂O₄ had 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.