CELL-VOLUME REGULATION IN HUMAN NEUTROPHILS - 2-(AMINOMETHYL)PHENOLS AS CL- CHANNEL INHIBITORS

When subjected to hypotonic stress, human peripheral neutrophils initi ally swell due to rapid water entry and thereafter recover toward the normal cell size (approximately 330 mum3). Neutrophils do not behave a s perfect osmometers: when resuspended in half-isotonic medium (150 mo sM), they swell by only approximately 40% rather than doubling in size as predicted for ideal behavior. As with lymphocytes, restoration to the normal cell size involves the net loss of K+ and Cl- from the cyto sol through independent conductance pathways. Volume regulation is sen sitive to 0.4-1 mM of quinine, UK-5099, 3,5-diiodosalicylate (DISA), M K-473 (an indanyloxyacetate derivative), and to MK-447 [a 2-(aminometh yl)phenol]. From correlation of drug effects on the time course of cel l volume recovery and the associated volume-activated Rb-86+ and Cl-36 - fluxes, it was evident that quinine blocked only K+ channels, wherea s MK-447 acted as a selective inhibitor of Cl- channels. In contrast, UK-5099, DISA, and MK-473 were nonspecific in that the compounds displ ayed comparable suppressive effects on all three parameters. Structure -activity relationships in the MK-447 series revealed the critical ele ments of the molecule responsible for drug potency. In particular, the importance of the neighboring ionizable 1-hydroxyl and 2-aminomethyl groups and the formation of secondary ring structures for biological a ctivity is emphasized. The most potent derivative thus far identified, termed analogue A [inhibitor constant (K(i)) approximately 16 muM], h ad a potency approximately sixfold greater than that of the parent com pound (K(i) approximately 90 muM). These findings define the mechanism of action of a relatively new class of agents that behave as inhibito rs of swelling-activated Cl- channels in these cells.