Cl- secretion by cultured shark rectal gland cells. III. Ca2+ regulation of apical membrane Cl- conductance.
Calcium ionophores (ionomycin and A-23187) were employed to assess the effects of increased intracellular Ca2+ concentration ([Ca2+]i) on apical membrane Cl- conductance (GaCl) and rate of transepithelial Cl- secretion in cultured shark rectal gland (SRG) cells. Apical 2 microM ionomycin induced dramatic changes in cellular electrophysiological properties: the apical membrane electrical potential difference (V(a)) depolarized from -66 mV to -46 mV, the fractional resistance of the apical membrane (fRa) decreased from 0.88 to 0.23, and the transepithelial electrical potential difference (Vab) increased slightly from +1.2 mV to +1.4 mV. These effects result from increased GaCl because apical low-Cl- shark Ringer (SR) depolarized V(a) by 32 mV and increased fRa from 0.23 to 0.36. Ionomycin-stimulated Vab or short-circuit current (Isc) results largely from increased Cl- secretion because approximately 80% of the increase in Isc is Cl- dependent. Establishing the Ca2+ dependence of ionophore activation of GaCl was confounded because apical low-Ca2+ SR [Ca2+ concentration ([Ca2+]) 1 mM to 0.1 microM] alone activated this conductive pathway. To establish the Ca2+ dependence of ionophore action, we assessed the effect of ionomycin on Isc in low-Ca2+ SR ([Ca2+] = 0.1 microM) and in SR. In low-Ca2+ SR, apical ionomycin stimulated Isc by 14.0 microA/cm2. In SR (normal [Ca2+]), ionomycin increased Isc further by 27.0 microA/cm2. Superfusing the basolateral surface with 2 microM ionomycin for 8-16 min failed to activate GaCl. In every case, subsequent superfusion of the apical surface with ionophore for 1.5-2 min activated GaCl. Bilateral 4 microM indomethacin (45-min superfusion) failed to block the ionomycin-induced GaCl.(ABSTRACT TRUNCATED AT 250 WORDS)
Moran
W M
WM
Department of Biology, University of Central Arkansas, Conway 72032.
Valentich
J D
JD
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism* / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D004553:Electric Conductivity; D007213:Indomethacin / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D009994:Osmolar Concentration; D012491:Salt Gland / Q000166:cytology / Q000378:metabolism* / Q000502:physiology*; D012754:Sharks
D002712:Chlorides; D005576:Colforsin; D000001:Calcimycin; D015759:Ionomycin; D002118:Calcium; D007213:Indomethacin