Ca2+ regulated K+ and non-selective cation channels in the basolateral membrane of rat colonic crypt base cells.
We have previously shown that a new type of K+ channel, present in the basolateral membrane of the colonic crypt base (blm), is necessary for cAMP-activated Cl- secretion. Under basal conditions, and when stimulated by carbachol (CCH) alone, this channel is absent. In the present patch clamp-study we examined the ion channels present in the blm under cell-attached and in cell-excised conditions. In cell-attached recordings with NaCl-type solution in the pipette we measured activity of a K+ channel of 16 +/- 0.3 pS (n = 168). The activity of this channel was sharply increased by CCH (0. 1 mmol/l, n = 26). Reduction of extracellular Ca2+ to 0.1 mmol/l (n = 34) led to a reversible reduction of activity of this small channel (SKCa). It was also inactivated by forskolin (5 micromol/l, n = 38), whilst the K+ channel noise caused by the very small K+ channel increased. Activity of non-selective cation channels (NScat) was rarely observed immediately prior to the loss of attached basolateral patches and routinely in excised patches. The NScat, with a mean conductance of 49 +/- 1.0 pS (n = 96), was Ca2+ activated and required >10 micromol/l Ca2+ (cytosolic side = cs). It was reversibly inhibited by ATP (<1 mmol/l, n = 13) and by 3',5-dichloro-diphenylamine-2-carboxylate (10-100 micromol/l, n = 5). SKCa was also Ca2+ dependent in excised inside-out basolateral patches. Its activity stayed almost unaltered down to 1 micromol/l (cs) and then fell sharply to almost zero at 0.1 micromol/l Ca2+ (cs, n = 12). SKCa was inhibited by Ba2+ (n = 31) and was charybdotoxin sensitive (1 nmol/l) in outside-out basolateral patches (n = 3). Measurements of the Ca2+ activity ([Ca2+]i) in these cells using fura-2 indicated that forskolin and depolarization, induced by an increase in bath K+ concentration to 30 mmol/l, reduced [Ca2+]i markedly (n = 8-10). Hyperpolarization had the opposite effect. The present data indicate that the blm of these cells contains a small-conductance Ca2+-sensitive K+ channel. This channel is activated promptly by very small increments in [Ca2+]i and is inactivated by a fall in [Ca2+]i induced by forskolin.
Bleich
M
M
Physiologisches Institut der Albert-Ludwigs-Universität, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany.
Riedemann
N
N
Warth
R
R
Kerstan
D
D
Leipziger
J
J
Hör
M
M
Driessche
W V
WV
Greger
R
R
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002217:Carbachol / Q000494:pharmacology; D002412:Cations; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology; D018118:Chloride Channels / Q000502:physiology; D002712:Chlorides / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000737:chemistry / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D007473:Ion Channels / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats
D002412:Cations; D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D015221:Potassium Channels; D005576:Colforsin; D001464:Barium; D000255:Adenosine Triphosphate; D002217:Carbachol; D000242:Cyclic AMP; D002118:Calcium