Effect of protein kinase C inhibitors on Cl- conductance required for volume regulation after L-alanine cotransport.

We used electronic cell sizing and Cl- efflux measurements in guinea pig jejunal enterocytes to study activation of Cl- conductance under two experimental conditions, regulatory volume decrease (RVD) after passive hypotonic swelling and volume regulation during Na(+)-alanine cotransport. RVD after a hypotonic (0.5 x isotonic) challenge was not affected by the protein kinase C (PKC) inhibitor 100 microM 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). Volume decrease after cell swelling in response to L-Ala (25 mM) was prevented by H-7 (P less than 0.05) or the more potent PKC inhibitor 10 nM staurosporine (P less than 0.001). L-Ala stimulated biphasic 36Cl efflux, a rapid efflux over 60 s which was inhibited by H-7 (P less than 0.01) and the Cl(-)-channel blocker anthracene-9-carboxylic acid (9-AC) (P less than 0.005). In contrast, after hypotonic dilution the rate of 36Cl efflux increased (P less than 0.005); H-7 had no effect but 9-AC inhibited the increase (P less than 0.01). Gramicidin (0.5 microM) added to cells maximally swollen by L-Ala in Cl(-)-containing medium caused 2 degree swelling (P less than 0.001), but 10 nM staurosporine reduced this 2 degree swelling (P less than 0.001). Addition of phorbol ester or synthetic diacylglycerol to villus cells under isotonic conditions, after gramicidin addition, caused cell swelling (P less than 0.005) that was inhibited by staurosporine (P less than 0.05). We concluded that PKC does not activate Cl- conductance for hypotonic RVD but that Na(+)-nutrient cotransport is a physiological stimulus for PKC to activate Cl- conductance necessary for volume regulation.