The cAMP-regulated and 293B-inhibited K+ conductance of rat colonic crypt base cells.
We have shown previously that secretagogues acting via the second messenger adenosine 3',5'-cyclic monophosphate (cAMP) activate, besides their marked effect on the luminal Cl- conductance, a K+ conductance in the basolateral membrane of colonic crypt cells. This conductance is blocked by the chromanol 293B. This K+ conductance is examined here in more detail in cell-attached (c.a.) and cell-excised (c.e.) patch- clamp studies. Addition of forskolin (5 micromol/l) to the bath led to the activation of very small-conductance (probably < 3 pS) K+ channels in c.a. patches (n = 54). These channels were reversibly inhibited by the addition of 0.1 mmol/l of 293B to the bath (n = 21). Noise analysis revealed that these channels had fast kinetics and produced a Lorentzian noise component with a corner frequency (fc) of 308 +/- 10 Hz (n = 30). The current/voltage curves of this noise indicated that the underlying ion channels were K+ selective. 293B reduced the power density of the noise (So) to 46 +/- 8.7% of its control value and shifted fc from 291 +/- 26 to 468 +/- 54 Hz (n = 8). In c.e. patches from cells previously stimulated by forskolin, the same type of current persisted in 3 out of 18 experiments when the bath solution was a cytosolic-type solution without adenosine 5'-triphosphate (ATP) (CYT). In 15 experiments the addition of ATP (1 mmol/l) to CYT solution was necessary to induce or augment channel activity. In six experiments excision was performed into CYT + ATP solution and channel activity persisted. 293B exerted a reversible inhibitory effect. The channel activity was reduced by 5 mmol/l Ba2+ and was completely absent when K+ in the bath was replaced by Na+. These data suggest that forskolin activates a K+ channel of very small conductance which can be inhibited directly and reversibly by 293B.
Warth
R
R
Physiologisches Institut der Albert-Ludwigs-Universität, Hermann-Herder-Strasse 7, D-79104 Freiburg i. Br., Germany.
Riedemann
N
N
Bleich
M
M
Van Driessche
W
W
Busch
A E
AE
Greger
R
R
D000818:Animals; D002839:Chromans / Q000494:pharmacology*; D003106:Colon / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D004553:Electric Conductivity; D004560:Electricity; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000502:physiology*; D051381:Rats; D013449:Sulfonamides / Q000494:pharmacology*
D002839:Chromans; D013449:Sulfonamides; C103474:6-cyano-4-(N-ethylsulfonyl-N-methylamino)-3-hydroxy-2,2-dimethylchromane; C029141:2,2,5,7,8-pentamethyl-1-hydroxychroman; D000242:Cyclic AMP; D011188:Potassium