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 differen t channels were seen. A large outwardly rectified K+ channel (BK) (con ductance, g at 0 mV = 92 +/- 6 pS), which was highly selective for K[P-K(+) (1) > P-Rb(+) (0.6) much greater than P-Cs(+) (0.09) approxima te to 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 appeare d 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 wa s 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 patch es, had a linear I/V (g = 38 +/- 3 pS), ran-down in O/C patches, and w as not seen in I/O patches. A number of smaller channels (SC) with con ductances ranging from 5 to 20 pS were seen in 16% of O/C patch es. Al so 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. TCOR had an outwardly rectified conductance (g at 0 mV = 36 +/- 2 pS), its P-o was independent of voltage and unaffected by var iations 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+] (greater than or equal to 10 mu mol/l), but was reduced by cytoplasmic ATP. None of the basolateral channels described here were activated by cAMP-depend ent secretagogues, although a Cl- conductance was activated. This cAMP -dependent Cl- conductance was distinct from the basolateral Cl- chann el and thus is most likely located in the apical membrane.