EFFECT OF LOWERED EXTRACELLULAR PH ON CA-2+-DEPENDENT K+ CURRENTS IN TYPE-I CELLS FROM THE NEONATAL RAT CAROTID-BODY

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 at 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 microM‐Bay K 8644. It could also be suppressed by bath application of 100 microM‐Cd2+ or 5 microM‐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 currents 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 microM‐Bay K 8644 and abolished in the presence of 5 microM‐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. © 1990 The Physiological Society