Effects of hypoxia on membrane potential and intracellular calcium in rat neonatal carotid body type I cells.

1. We have studied the effects of hypoxia on membrane potential and [Ca2+]i in enzymically isolated type I cells of the neonatal rat carotid body (the principal respiratory O2 chemosensor). Isolated cells were maintained in short term culture (3-36 h) before use. [Ca2+]i was measured using the Ca(2+)-sensitive fluoroprobe indo-1. Indo-1 was loaded into cells using the esterified form indo-1 AM. Membrane potential was measured (and clamped) in single isolated type I cells using the perforated-patch (amphotericin B) whole-cell recording technique. 2. Graded reductions in PO2 from 160 Torr to 38, 19, 8, 5 and 0 Torr induced a graded rise of [Ca2+]i in both single and clumps of type I cells. 3. The rise of [Ca2+]i in response to anoxia was 98% inhibited by removal of external Ca2+ (+1 mM EGTA), indicating the probable involvement of Ca2+ influx from the external medium in mediating the anoxic [Ca2+]i response. 4. The L-type Ca2+ channel antagonist nicardipine (10 microM) inhibited the anoxic [Ca2+]i response by 67%, and the non-selective Ca2+ channel antagonist Ni2+ (2 mM) inhibited the response by 77%. 5. Under voltage recording conditions, anoxia induced a reversible membrane depolarization (or receptor potential) accompanied, in many cases, by trains of action potentials. These electrical events were coincident with a rapid rise of [Ca2+]i. When cells were voltage clamped close to their resting potential (-40 to -60 mV), the [Ca2+]i response to anoxia was greatly reduced and its onset was much slower.(ABSTRACT TRUNCATED AT 250 WORDS)