Evidence for Na+/Ca2+ exchange in the rectal gland of Squalus acanthias.
Previously we have shown that stimulation of in vitro perfused rectal gland tubules (RGT) of the dog-fish Squalus acanthias by adenosine 3',5'-cyclic monophosphate (cAMP), (as a cocktail comprising 0.1 mmol/l dibutyryl-cAMP, 10 micromol/l forskolin and 0.1 mmol/l adenosine, hereafter termed STIM) leads to an increase in cytosolic Ca2+ ([Ca2+]i) and that this assists Cl- secretion by enhancing basolateral K+ conductance. In the present study we examined the mechanism of the cAMP-induced increase in [Ca2+]i. [Ca2+]i was measured using the fura-2 technique in isolated in vitro perfused RGT. As before, STIM enhanced [Ca2+]i. This elevation of [Ca2+]i was prevented completely when STIM was added in the presence of the Na+2Cl-K+ cotransport inhibitor furosemide (0.5 mmol/l). This suggests that the increase in [Ca2+]i induced by STIM is caused by a concomitant increase in cytosolic Na+ ([Na+]i) and not by the activation of second messenger cascades. Furosemide prevents this increase in [Na+]i and hence the elevation of [Ca2+]i. Moreover, the plateau phase of the [Ca2+]i transient produced by carbachol (CCH, 0.1 mmol/l) was augmented strongly when bath Na+ was reduced to 5 mmol/l. These data suggest that the level of [Ca2+]i is determined by Na(+)-dependent Ca2+ export, most likely via a Na+/Ca2+ exchanger. The increase in [Na+]i accompanying stimulation of Cl- secretion reduces the rate of Ca2+ export leading to an elevation of [Ca2+]i, as does a reduction in bath Na+ which augments the [Ca2+]i plateau produced by CCH.
Bleich
M
M
Physiologisches Institut, Albert-Ludwigs-Universität, Freiburg, Germany. bleich@uni-freiburg.de
Hug
M J
MJ
Heitzmann
D
D
Warth
R
R
Greger
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004232:Diuretics / Q000494:pharmacology; D004284:Dogfish / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D018721:Muscarinic Agonists / Q000494:pharmacology; D012491:Salt Gland / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013268:Stimulation, Chemical
D004232:Diuretics; D005456:Fluorescent Dyes; D018721:Muscarinic Agonists; D019831:Sodium-Calcium Exchanger; D005665:Furosemide; D002217:Carbachol; D012964:Sodium; D000242:Cyclic AMP; D002118:Calcium; D016257:Fura-2