Effect of lowered extracellular pH on Ca2(+)‐dependent K+ currents in type I cells from the neonatal rat carotid body.

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Abstract
1. The whole-cell configuration of the patch-clamp technique was used to record K+ currents from type I cells enzymatically dispersed from the neonatal rat carotid body. The current-voltage (I-V) relationship for the K+ currents showed a prominent, outward shoulder to test potentials of between +10 and +30 mV. 2. The shoulder of the I-V curve could be enhanced by raising extracellular Ca2+ concentration or by bath application of 5 .mu.M-Bay K 8644. It could also be suppressed by bath application of 100 .mu.M-Cd2+ or 5 .mu.M-methoxyverapamil (D600), indicating that a large component of the K+ current in these cells was activated by an influx of Ca2+ through its own channels during cell depolarization. 3. Potassium contents were also reversibly suppressed by 8 nM-charybdotoxin but unaffected by 100 nM-apamin, suggesting that the Ca2+-dependent K+ current was carried through large or intermediate conductance Ca2+-activated K+ channels. 4. Lowering the pH of the bathing medium from 7.40 to 7.00 reversibly reduced the K+ current amplitudes, and suppressed the shoulder normally seen in the I-V relationship. This effect was enhanced in the presence of 5 .mu.M-Bay K 8644 and abolished in the presence of 5 .mu.M-D600. 5. It is concluded that the Ca2+-dependent K+ channels of type I carotid body cells are selectively suppressed by extracellular acidity. Possible mechanisms underlying this effect, and its role in excitation of the carotid body are discussed.