Roles of Ca and cAMP on Cl Channel Activity in Cystic Fibrosis Sweat Clear Cells as Studied by Microsuperfusion and Cell Volume Analysis
In an attempt to study regulation of Cl channels in intact sweat secretory coils in cystic fibrosis and controls in the least invasive manner, isolated secretory coils were superfused with various drugs and K-efflux was determined as an indirect measure of Cl movement. Cl channel activity was also determined from the drug-induced cell volume increase in gramicidin (GC)-treated dissociated eccrine clear cells. We observed that while MCh-induced K-efflux from the CF secretory coils was entirely normal, K-efflux in the presence of isoproterenol (ISO), forskolin (FK), or IBMX was absent in CF, suggesting that these agents failed to stimulate Cl movement. Cl channel activity of dissociated CF clear cells, as studied by cell volume analysis, was entirely normal when stimulated by Ca-elevating agents but was defective when stimulated by cAMP-elevating agents. TPA (phorbol ester) does not appear to stimulate Cl channel activity nor does it modify the effect of other agents. The following observations from the present and previous studies are not necessarily consistent with the traditional thesis that the observed Cl movement is due to cAMP: CT-cAMP had no effect on cell swelling or on K-efflux; ISO is more potent in accumulating tissue cAMP than IBMX yet the latter is more potent in stimulating K-efflux; IBMX increases cytoplasmic [Ca] yet is unable to stimulate K-efflux in CF; K-efflux stimulated by cAMP-elevating agents was inhibited by removal of Ca from the bath; and, cell swelling of GC-treated cells in response to cAMP elevating agents was inhibited by removal of Ca. The inability of IBMX to stimulate Cl channels in the face of elevated cytoplasmic [Ca] and cAMP in CF cells deserves further scrutiny.
KeywordsCystic Fibrosis Clear Cell Sweat Gland Eccrine Sweat Gland Cystic Fibrosis Airway
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