Swelling- and cAMP-activated Cl- currents in isolated rat carotid body type I cells

1. In the whole-cell configuration of the patch clamp technique, isolated rat carotid body type I cells exhibited reversible activation of Cl- currents during cell swelling effected by hypotonic extracellular solutions. 2. Hypotonic solutions evoked outwardly rectifying, non-inactivating currents which showed time-independent activation. The reversal potential (E-rev) for the hypotonically evoked current was 1.6 +/- 0.6 mV (n = 26). Reduction of extracellular Cl- from 133 to 65.5 mM caused a shift in E-rev of 14.7 +/- 0.4 mV (n = 5). 3. The swelling-activated Cl- current could not activate when ATP was omitted from the patch pipette or when substituted for the non-hydrolysable ATP analogues 5'-adenylylimidodiphosphate, AMP-PNP (2 mM) or beta,gamma-methylene-adenosine 5'-triphosphate, AMP-PCP (2 mM). The current also failed to activate in the absence of free intracellular Ca2+. 4. The swelling-activated Cl- current was sensitive to blockade by the Cl- channel blockers niflumic acid (300 mu M) and 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS; 200 mu M), although the blockade by DIDS was voltage dependent. 5. A similar, non-inactivating, outwardly rectifying Cl- current was evoked by the inclusion of cAMP (200 mu M) in the patch pipette. This current could be inhibited by niflumic acid (300 mu M), DIDS (200 mu M) and hypertonic solutions, and was virtually abolished in the absence of intracellular ATP. 6. In conclusion, carotid body type I cells possess Cl- currents activated by cell swelling and rises in intracellular cAMP concentration. These currents may be involved in cell volume regulation, blood volume and osmolarity regulation and the response of the type I cell to chemostimuli.