Ion channels in isolated mouse jejunal crypts

 The patch-clamp technique was used to characterise the ion channels in cells located in the mid region of mouse jejunal crypts. Six different channels were seen. A large outwardly rectified K⁺ channel (BK) (conductance, g at 0 mV = 92 ± 6 pS), which was highly selective for K⁺ P _K ⁺ (1) > P _Rb ⁺ (0.6) >> P _Cs ⁺ (0.09) ≈ P _Na ⁺ (0.07) > P _Li ⁺ (0.04)], had a low, voltage-independent open probability (P _o) in the on-cell (O/C) configuration and appeared in 66% of the patches. In inside-out (I/O) patches, this channel had a linear current/voltage (I/V) relationship (g = 132 ± 3 pS), P _o was voltage dependent and it was blocked by cytoplasmic Ba²⁺ (5 mmol/l). An intermediate K⁺ channel (IK) which was present in 49% of O/C patches, had a linear I/V (g = 38 ± 3 pS), ran-down in O/C patches, and was not seen in I/O patches. A number of smaller channels (SC) with conductances ranging from 5 to 20 pS were seen in 16% of O/C patches. Also present in the basolateral membrane were a Cl^– channel (ICOR) and a nonselective cation channel (NSCC). These channels were only seen in I/O patches. ICOR had an outwardly rectified conductance (g at 0 mV = 36 ± 2 pS), its P _o was independent of voltage and unaffected by variations in cytoplasmic Ca²⁺ (100 nmol/l to 1 mmol/l) or ATP (0–1 mmol/l). The NSCC had a linear conductance (20 ± 1 pS), its P _o increased with depolarisation and elevation of cytoplasmic Ca²⁺] (≥ 10 μmol/l), but was reduced by cytoplasmic ATP. None of the basolateral channels described here were activated by cAMP-dependent secretagogues, although a Cl^– conductance was activated. This cAMP-dependent Cl^– conductance was distinct from the basolateral Cl^– channel and thus is most likely located in the apical membrane. Received: 25 June 1997 / Accepted: 14 October 1997