Differences in Ca(2+)-mediation of hypotonic and Na(+)-nutrient regulatory volume decrease in suspensions of jejunal enterocytes.
We determined differences in the Ca2+ signalling of K+ and Cl- conductances required for Regulatory Volume Decrease (RVD) in jejunal villus enterocytes passively swollen (0.5 or 0.95.isotonic) compared with swelling because of the absorption of D-glucose (D-Glc) or L-Alanine (L-Ala). Cell volume was measured using electronic cell sizing. In nominally Ca(2+)-free medium containing EGTA (100 microM) RVD after 0.5 or 0.95.isotonic challenge was prevented. L-Ala swelling and subsequent RVD was influenced in Ca(2+)-free medium. Villus cells were incubated with 10 microM of the acetomethoxy derivative of 1,2.bis (2-aminophenoxy) ethane N,N,N1,N1 tetracetic acid (BAPTA-AM) and RVD after 0.5.isotonic swelling or L-Ala swelling was prevented. Niguldipine (0.1 microM), nifedipine (5 microM), diltiazem (100 microM), Ni2+, and Co2+ (1 mM) all prevented hypotonic RVD but had no effect on RVD after L-Ala addition. Charybdotoxin (25 nM) a potent inhibitor of Ca(2+)-activated K+ channels, had no effect on hypotonic RVD but prevented RVD of villus cells swollen by D-Glc. We used the calmodulin antagonists, naphthalene sulfonamide derivatives W-7 and W-13, to assess calmodulin activation of K+ and Cl- conductance in these two models. L-Ala swelling and subsequent RVD was not influenced by 25 microM W-7; hypotonic RVD was prevented by 25 microM W-7 or 100 microM W-13. The W-13 inhibition of RVD was by-passed with 0.5 microM gramicidin. Our data show that hypotonic RVD requires extracellular Ca2+ and that the K+ conductance activated is not charybdotoxin sensitive but requires calmodulin.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002147:Calmodulin / Q000037:antagonists & inhibitors; D048429:Cell Size / Q000187:drug effects; D018999:Charybdotoxin; D004110:Diltiazem / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006168:Guinea Pigs; D007038:Hypotonic Solutions; D007202:Indicators and Reagents; D007583:Jejunum / Q000166:cytology* / Q000502:physiology; D008297:Male; D008871:Microvilli / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D012604:Scorpion Venoms / Q000494:pharmacology; D012964:Sodium / Q000502:physiology*; D013535:Suspensions
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002147:Calmodulin; D007038:Hypotonic Solutions; D007202:Indicators and Reagents; D015221:Potassium Channels; D012604:Scorpion Venoms; D013535:Suspensions; D018999:Charybdotoxin; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D012964:Sodium; D004110:Diltiazem; D002118:Calcium