Ca2+ channel currents in type I carotid body cells of normoxic and chronically hypoxic neonatal rats.

Whole-cell patch-clamp recordings were used to study voltage-gated Ca2+ channel currents in type I carotid body cells of young rats born and reared in normoxia or in a chronically hypoxic (CH) environment (10% O2). Currents activated at potentials of -40 mV and more positive, and typically peaked at 0 mV in both groups of cells. Steady-state inactivation curves were similar in the two populations. Ca2+ currents were significantly larger in CH type I cells, but this was accounted for by the increased size of CH cells: current density was similar in both cell types. Nifedipine (5 microM) always partially inhibited currents and Bay K 8644 (2-5 microM) always enhanced currents, indicating the presence of L-type channels. In a small number of cells from each group, the N-type channel blocker omega-conotoxin GVIA caused partial, irreversible inhibition, but in most cells was without discernible effect. These results indicate that type I cells possess L-type Ca2+ channels, that N-type are expressed in some cells and that non-L, non-N-type channels are also present. Furthermore, chronic hypoxia does not appear to cause specific adaptive changes in the properties of Ca2+ channels in type I cells.