Dc. Devor et al., CAMP-ACTIVATED CL- CHANNELS IN PRIMARY CULTURES OF SPINY DOGFISH (SQUALUS-ACANTHIAS) RECTAL GLAND, American journal of physiology. Cell physiology, 37(1), 1995, pp. 70-79
Whole cell and single-channel patch-clamp techniques were used to iden
tify and characterize the Cl-currents responsible for adenosine 3',5'-
cyclic monophosphate (cAMP)-mediated Cl- secretion in the rectal gland
of the spiny dogfish (Squalus acanthias). During whole cell recording
s, in cultured rectal gland cells forskolin (10 mu M) and 8-(4-chlorop
henylthio)adenosine 3',5'-cyclic monophosphate (400 mu M) Stimulated a
28-fold increase in Cl- conductance (n = 10). This cAMP-activated con
ductance pathway had a linear current-voltage (I-V) relationship that
was time and voltage independent. Substitution of 235 meg Cl- with I-
in the bath inhibited the cAMP-activated current at both positive and
negative voltages (64%). Glibenclamide (60 mu M) abolished the cAMP-st
imulated current, and its effect was irreversible (n = 3). During cell
-attached recording, increased cellular cAMP activated single Cl- chan
nels in nine previously quiet patches. These channels had a linear I-V
relationship with an average single-channel conductance of 5.1 +/- 0.
2 pS (n = 6). Similar properties were observed in excised inside-out p
atches, permitting further characterization of the single-channel prop
erties. Excised quiescent patches could be activated by the addition o
f ATP and protein Kinase A. Replacing bath Cl- with I-inhibited both i
nward and outward currents (n = 3). In three inside-out patches, glibe
nclamide (300 mu M) reversibly reduced open probability by 74%, with n
o effect on single-channel current amplitude. Similar results were obt
ained in four outside-out recordings. These results suggest that incre
ased cellular cAMP in dogfish rectal gland activates a small linear Cl
- channel that resembles human cystic fibrosis transmembrane conductan
ce regulator in its biophysical and pharmacological properties.